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EEVblog => EEVblog Specific => Topic started by: EEVblog on July 11, 2018, 09:16:41 am

Title: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: EEVblog on July 11, 2018, 09:16:41 am
Teardown on the Omicron Labs Bode 100 Frequency Response Analyser / Vector Network Analyser

http://www.youtube.com/watch?v=IpI-cGU6-FY (http://www.youtube.com/watch?v=IpI-cGU6-FY)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: jbb on July 11, 2018, 10:09:54 am
I guess some of the DG4xx switches are being used as precision mixers (and others used to switch filter banks etc.).

It could be very interesting to (carefully!) probe the outputs of the two DDS units. I suspect that they run at different frequencies to do the heterodyne mixing. Also keep an eye out for high speed comparators to turn the sine wave frequency reference into square waves to drive switches.

On the directional coupler front, I think your previous video showed a 50 Ohm series resistor with a differential amplifier across it. Maybe they’re doing electronic measurement because it would be very hard to make an RF coupler work at the lower frequency range.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: JS on July 11, 2018, 10:31:50 am
The reflection is easy to measure as they have access to the generators output previous to the 50Ω resistor, software is clear enough they are using that.

The second dds is likely to generate the IF for the mixer, what I haven't seen is the mixer, as said the only mixy thing there are the switches but filtering that is kind of a pain, as switching mixer generates lot of side bands, should do the math for that. They could run the second dds at the same freq of the first, 90° out of phase and take down to dc in phase and cuadrature to meassure the signal, but that would take too long to settle at each step. ADC is too slow to make wide bands conversions but they are likely to still be using a fixed freq and just switch the bw of the filter. Missing a 3rd dds to make for the cuadrature reference.

We have all we need to reverse engineer that transformer! Construction method, number of turns, impedance analysis, freq response... It's just matter of finding the right core material, with the impedance and number of turns permeability could be estimated... Would someone sell cores out of that material?

JS
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 11, 2018, 11:14:25 am
I tried to make a modest homebrew version of this and the best solution I found for injection transformers were current transformers for AC current measurement where I added some primary windings:

https://electronicprojectsforfun.wordpress.com/injection-transformers/

You have to be cautious with frequency ranges advertised; these are -3dB values, and phase shift at the band corners can be too much for meaningful measurements.
Another issue is the capacitance between primary and secondary. This could be way above 100pF due to the bifilar winding technique, maybe too much for some sensible circuits.



Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Bud on July 11, 2018, 11:48:19 am
. Missing a 3rd dds to make for the cuadrature reference.

You can generate quadrature LO sequentially with a single DDS as it is done in the N2PK VNA.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Bud on July 11, 2018, 11:54:34 am
what I haven't seen is the mixer, as said the only mixy thing there are the switches but filtering that is kind of a pain, as switching mixer generates lot of side bands, should do the math for that.

Filtering may not be needed, it depends on the architecture. VNAs are less demanding to filtering. Some, like the VNWA, dont have filtering at all. Moreover, it makes use of the aliases as  the operating principle per se and to extend the bandwidth.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: station240 on July 11, 2018, 12:51:36 pm
Although it doesn't answer your question on what the wideband transformer winding style is, this page does explain why it's done that way.
http://www.richieburnett.co.uk/temp/gdt/gdt1.html (http://www.richieburnett.co.uk/temp/gdt/gdt1.html)
(unfinished page)

I think the real trick is in the brown ferrite core itself, the colours denote frequency/saturation properties, I have heaps of rings but not any brown ones which I assume are RF ones.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Bud on July 11, 2018, 01:09:53 pm
Do not seem to be a RF core to me but rather a low freq material. The trick is in the bifilar coupled winding and the ransformer will work with no core at upper frequencies. The core kicks in at lower frequencies to increase the windings impedance. This is widely used in RF baluns to achieve wide frequency range.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: JS on July 11, 2018, 02:18:41 pm
Hi, Ive done my homework and I'm back, but first.

Filtering may not be needed, it depends on the architecture. VNAs are less demanding to filtering. Some, like the VNWA, dont have filtering at all. Moreover, it makes use of the aliases as  the operating principle per se and to extend the bandwidth.
  Right, if the only thing you are interested is amplitude that's true, non linearities would be harder to pick this was as high freq harmonics will fall well beyond the ADC's bandwidth and it won't be able to determine a lot of factors. Anyway, even if filtering is done it will only catch LF harmonics and might get trickier as freq increases. I did used oversampling building something in the past, as long as you are only interested in the amplitude and missing a few narrow bands isn't a problem the only HF limiting factor is the sampling time of the sample and hold circuit. I mostly have an audio background and for HF stuff sometimes it seems more like a luggage than a background, it bites me every time.

Although it doesn't answer your question on what the wideband transformer winding style is, this page does explain why it's done that way.
http://www.richieburnett.co.uk/temp/gdt/gdt1.html (http://www.richieburnett.co.uk/temp/gdt/gdt1.html)
(unfinished page)

I think the real trick is in the brown ferrite core itself, the colours denote frequency/saturation properties, I have heaps of rings but not any brown ones which I assume are RF ones.
  Here is my homework, the thing seems to have 39 turns 40 turns, (I knew it couldn't be 39, my numbers are still with 39 but they should be pretty close anyway) if I know how to count, in the previous video we can see the impedance, 400Ω @ 300Hz means 210mH, that's AL = 140µH/N^2
  I estimated the size of the core, roughly a T184 core, height 18mm, outer diameter 47mm, inner diameter 25mm means a permeability of about 60000, seems like a lot but I was expecting something like that, small signal audio transformer use that kind of core permeability, low turn count low freq was asking for that, now let's look for a brown core with tens of thousands for µr... there are not that many materials in that range...
  I would bet it's nanoperm https://www.magnetec.de/en/nanopermr-products/, (https://www.magnetec.de/en/nanopermr-products/,) it's the closer one I found.
  Here are some products, http://www.feryster.com/polski/nanoperm.php?lang=en (http://www.feryster.com/polski/nanoperm.php?lang=en)
  There's one with 40mm outside diameter, 25mm inside diameter and 15mm height, permeability of 75000, I gotchya!
  Oh s***t, it's blue! http://allegro.pl/rdzen-magnetec-m-083-rtn-40x25x15-nanoperm-i7430998721.html (http://allegro.pl/rdzen-magnetec-m-083-rtn-40x25x15-nanoperm-i7430998721.html) I don't know, I can't find the actual one, this looks like the closest, but still could work. I couldn't find a way to source the cores, always hard here in Argentina, if someone can source them would be cool to see some tests.

  Hf response would only depend on the parasitic inductance and capacitance, to keep inductance low they have twisted the wires, to get low capacitance low turns count and thick insulators, the tricky part is the low frequency. I do have some audio transformers I could use, they go up to tens of kHz but LF response is better than seen in the first video, having a few Henry inductance, after that a different transformer could jump in and make up for the rest of the way.

  @EEVblog pleeeeeeease grab some calippers and measure that core!!!  :popcorn:

JS

Edited...
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on July 11, 2018, 05:13:31 pm
That's not ferrite and it's definitely not powdered iron, that's got to be nanocrystalline and nothing else. :)  Most likely Vacuumschmeltze, probably https://www.mouser.com/ProductDetail/Vacuumschmelze/T60006-L2040-W453?qs=sGAEpiMZZMs2JV%252bnT%2fvX8PvC43ppqs%252bksq4V5kp6Ay4%3d (https://www.mouser.com/ProductDetail/Vacuumschmelze/T60006-L2040-W453?qs=sGAEpiMZZMs2JV%252bnT%2fvX8PvC43ppqs%252bksq4V5kp6Ay4%3d) or similar.

  Oh s***t, it's blue! http://allegro.pl/rdzen-magnetec-m-083-rtn-40x25x15-nanoperm-i7430998721.html (http://allegro.pl/rdzen-magnetec-m-083-rtn-40x25x15-nanoperm-i7430998721.html) I don't know, I can't find the actual one, this looks like the closest, but still could work. I couldn't find a way to source the cores, always hard here in Argentina, if someone can source them would be cool to see some tests.

Never seen any in blue, I wonder if they got them as special order, or if there's another mfg I don't know about.  IIRC, it was just VAC and HMG (former Metglas) doing rapid-quench materials, but maybe there's new ones from China I don't know about?

Checking, I see very little on Ali Express, so probably not.

Quote
Hf response would only depend on the parasitic inductance and capacitance, to keep inductance low they have twisted the wires, to get low capacitance low turns count and thick insulators, the tricky part is the low frequency. I do have some audio transformers I could use, they go up to tens of kHz but LF response is better than seen in the first video, having a few Henry inductance, after that a different transformer could jump in and make up for the rest of the way.

HF response is easily calculated from the transmission line length.  It's a transmission line transformer, simple as that.  The twisted pair will have Zo ~ 100 ohms, so that for a step input, each port of the transmission line looks like 100 ohms.  That is, the equivalent circuit for short transients is:
pri start -- 100 ohms -- sec start
|                                      |
~open circuit       ~open circuit
|                                      |
pri end -- 100 ohms -- sec start

The open circuit is because the core gives the transmission line a very large common mode impedance, i.e., the two ports act as ideal ports, with no common mode connection (again, for short transients, but as it turns out, also for rather low frequencies, down to ~Hz).

After one transmission line delay, the start and end waves interfere with each other, and normal transformer action is had.

Note that this does NOT magically have extreme CMRR -- there's as little as 100 ohms, directly from primary to secondary (again, for short transients).  At frequencies well below the electrical length, it approximates as a capacitance from each end of primary, to the respective ends of the secondary.  (The exact capacitance can be calculated from line length and impedance.)

Likewise, leakage inductance is the LF equivalent of transmission line inductance, and can be calculated from length and impedance.

If the line is, say, 5m long (to take a ballpark guess), and vf ~ 0.8, then Cp = 208pF (total, so, say, 104pF where the 100 ohmses are indicated above), and LL = 1.67uH.

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: EEVblog on July 11, 2018, 05:18:39 pm
We have all we need to reverse engineer that transformer! Construction method, number of turns, impedance analysis, freq response... It's just matter of finding the right core material, with the impedance and number of turns permeability could be estimated... Would someone sell cores out of that material?

If you could sell a $100 unit with the same performance, you'd sell a truck load of them.
Would be interesting to try and duplicate their design and what performance it has with just some random core.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: EEVblog on July 11, 2018, 05:23:13 pm
Although it doesn't answer your question on what the wideband transformer winding style is, this page does explain why it's done that way.
http://www.richieburnett.co.uk/temp/gdt/gdt1.html (http://www.richieburnett.co.uk/temp/gdt/gdt1.html)
(unfinished page)

Many are saying it's a bifilar winding, and I actually said that in the video as my first guess, but I edited it out because I don't think it is.
I thought bifilar implies same coil opposite direction and (usually?) non twisted?
This one is opposite pair and twisted, totally different thing to a bifilar coil winding IMO  :-//
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on July 11, 2018, 05:26:40 pm
I thought bifilar implies same coil opposite direction and (usually?) non twisted?
This one is opposite pair and twisted, totally different thing to a bifilar coil winding IMO  :-//

I use "bifilar" and "twisted pair" interchangeably for winding purposes.

Hmm, I don't actually know if "bifilar" is, say, a brand name or something, and implies parallel wires glued together and laid flat.  In any case, the characteristics will be very much the same for either method (with the twisted pair being slightly worse just due to the twist taking up some velocity factor).

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: twistedresistor on July 11, 2018, 05:31:39 pm
Bifilar just means the wires are wound next to each other, regardless of the direction. The opposite would be sectional winding where the two windings are on opposite sides of the core, like seen in chokes for common mode line filters.

What intrigues me the most: When i spoke to the guys at Omicron they've told me that one challenge for the transformer was that it had to be low in capacitance. But the coupling capacitance in a bifilar winding is usually higher than a sectional wound inductor.

(EDIT: T3sl4co1l beat me to it. Bifilar is not a brand thing)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: tautech on July 11, 2018, 05:34:12 pm
Bifilar just the wires are wound next to each other, regardless of the direction.
That's as I understand it too.
Twisted pair is different.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: twistedresistor on July 11, 2018, 05:41:40 pm
A twisted pair has nothing to do with winding an inductor. You can wind a twisted pair around a core - that's what they did - then you got a bifilar wound inductor.

That's as I understand it too.
Twisted pair is different.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on July 11, 2018, 05:59:20 pm
What intrigues me the most: When i spoke to the guys at Omicron they've told me that one challenge for the transformer was that it had to be low in capacitance. But the coupling capacitance in a bifilar winding is usually higher than a sectional wound inductor.

Inseparable from the nature of the transformer -- you can make bank windings, but you royally screw the leakage inductance.  Basically making a very high impedance transmission line.  But with a lot of self-capacitance balled up in the sections, rather than shared, so the bandwidth is awful.

A typical bank wound CMC has Zo ~ 300 ohms and BW < 10MHz.  Zo isn't really that much higher, because of the self-capacitance.

This TLT will have BW out until TL effects cause peaks and notches; these are dampened when Zin and Zout are matched, i.e., 100 ohm source and load.  At 50 ohms, the peaking will be noticeable, and the cutoff will be a bit worse (about 1/2 bandwidth).

Incidentally, the rolloff will NOT be that silky smooth curve they showed.  You can see this in CMC datasheets, the ones that are bifilar wound (data chokes), there are multiple peaks and valleys in the diff mode response, because the measurement is made as a shorted transmission line.  That it has peaks, means your data will propagate safely all the way up there. :) (For common mode, that is.  For isolation mode, there are peaks.)

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Kleinstein on July 11, 2018, 06:20:56 pm
. Missing a 3rd dds to make for the cuadrature reference.

You can generate quadrature LO sequentially with a single DDS as it is done in the N2PK VNA.

There is no need for a quadrature LO if the ADC is not seeing zero IF, but more like an IF in the audio band. The 2 nd DDS would than be the LO, slightly offset from the output frequency. The quadrature part is than at the second virtual IF done in software.  So to a good part this is very similar to the simple SDR receivers. It is kind of doing the quadrature at a different time though more continuous phase shift instead of switching between 2 cases.

As the LO is used to drive CMOS switches as mixers, there would be digital LO signal and thus no problem generating quadrature signals with 2 D flip-flops and running the DDS at twice the LO. Still the ADC seems to be single channel only - so this way is likely not used, though it might offer slightly lower noise.

I would guess the FPGA might have enough processing power to do the IF processing and thus much less data transferred via USB. Using an FTDI USB chip also points to a rather low data rate.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: JS on July 11, 2018, 06:37:37 pm
We have all we need to reverse engineer that transformer! Construction method, number of turns, impedance analysis, freq response... It's just matter of finding the right core material, with the impedance and number of turns permeability could be estimated... Would someone sell cores out of that material?

If you could sell a $100 unit with the same performance, you'd sell a truck load of them.
Would be interesting to try and duplicate their design and what performance it has with just some random core.
I could certainly try, at least that would justify buying a decent freq gen for the lab. Could you measure the core size for me? First out would certainly be a mailbag for the EEV!

That's not ferrite and it's definitely not powdered iron, that's got to be nanocrystalline and nothing else. :)  Most likely Vacuumschmeltze, probably
That's for sure, the banner picture on the ones I posted had blue and brown cores, the ones I found for sale with the part numbers I was looking shown blue pictures but that's the only reference I got and I can't even read the web in that language!
Quote
...
HF response is easily calculated from the transmission line length.  It's a transmission line transformer, simple as that.  The twisted pair will have Zo ~ 100 ohms, so that for a step input, each port of the transmission line looks like 100 ohms.  That is, the equivalent circuit for short transients is:
pri start -- 100 ohms -- sec start
|                                      |
~open circuit       ~open circuit
|                                      |
pri end -- 100 ohms -- sec start

The open circuit is because the core gives the transmission line a very large common mode impedance, i.e., the two ports act as ideal ports, with no common mode connection (again, for short transients, but as it turns out, also for rather low frequencies, down to ~Hz).

After one transmission line delay, the start and end waves interfere with each other, and normal transformer action is had.

Note that this does NOT magically have extreme CMRR -- there's as little as 100 ohms, directly from primary to secondary (again, for short transients).  At frequencies well below the electrical length, it approximates as a capacitance from each end of primary, to the respective ends of the secondary.  (The exact capacitance can be calculated from line length and impedance.)

Likewise, leakage inductance is the LF equivalent of transmission line inductance, and can be calculated from length and impedance.

If the line is, say, 5m long (to take a ballpark guess), and vf ~ 0.8, then Cp = 208pF (total, so, say, 104pF where the 100 ohmses are indicated above), and LL = 1.67uH.

Tim
I would guess under 3m, 10MHz wavelength is 30m, about 20m inside the wire, so transmission line is not quite needed in this case, I think concentrated parameters should get to a reasonable guesstimate. Also, in the first video, HF impedance looks capacitive, which makes sense for me I guess. I didn't took the time to look for looking at HF as I was trying to get the core parameters.

Here is the plot
https://youtu.be/66s9easZKxU?t=35m42s
The plot shows 200Ω at 1MHz, that's about 800pF. That's in the ball park from 100kMHz to 7MHz. It looks too high to me but still being a lot of things around, which will be used with this transformer anyway, still looking pretty high... Phase is over 70º and parallel resistance looks like 2k so I don't know why such a high capactance, I could bet it's not from the winding. I've wound a few transformers and with a few hundred turns of enamel coated wire around a chunk of iron, trifilar wound, got about 5nF. This has shorter 40 turns of polymer insulated wire, not teflon, the solder melted a little of it...

Then a bit over 10MHz there is a resonation, that might be inductance of wires going to the transformer, after that it start to behaves as you see and there might be due to the wavelength getting closer to the winding length.

Bifilar just means the wires are wound next to each other, regardless of the direction. The opposite would be sectional winding where the two windings are on opposite sides of the core, like seen in chokes for common mode line filters.

What intrigues me the most: When i spoke to the guys at Omicron they've told me that one challenge for the transformer was that it had to be low in capacitance. But the coupling capacitance in a bifilar winding is usually higher than a sectional wound inductor.

(EDIT: T3sl4co1l beat me to it. Bifilar is not a brand thing)

The capacitance they needed to make low is probably the equivalent parallel capacitance of the secondary (refered to the secondary as it will act as a 2nd order LPF there together with the leakage inductance. I'm considering concentrated parameters, not transmission lines, but we are in a middle ground here at 10MHz. As said twisted wires gives the lower leakage inductance which is a very good thing for HF transformers.

. Missing a 3rd dds to make for the cuadrature reference.

You can generate quadrature LO sequentially with a single DDS as it is done in the N2PK VNA.

There is no need for a quadrature LO if the ADC is not seeing zero IF, but more like an IF in the audio band. The 2 nd DDS would than be the LO, slightly offset from the output frequency. The quadrature part is than at the second virtual IF done in software.  So to a good part this is very similar to the simple SDR receivers. It is kind of doing the quadrature at a different time though more continuous phase shift instead of switching between 2 cases.

As the LO is used to drive CMOS switches as mixers, there would be digital LO signal and thus no problem generating quadrature signals with 2 D flip-flops and running the DDS at twice the LO. Still the ADC seems to be single channel only - so this way is likely not used, though it might offer slightly lower noise.

I would guess the FPGA might have enough processing power to do the IF processing and thus much less data transferred via USB. Using an FTDI USB chip also points to a rather low data rate.
This post is getting long, as I write I receive more answers... ADC could still be multiplexed, time difference between corrected in DSP, as long as IF is low enough. I was expecting a balanced mixer making filtering easier, but we are in a digital world so digital it is, there was a 595 somewhere in there, so...

For the times it takes to the software to load a different measurement mode and the real time data plot, I would guess you are right about processing in the FPGA, if it would be just pushing data via USB there's nothing to load other than a different algorithm to ram, which I'd expect to be quicker load times, slower plotting.

JS
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 11, 2018, 08:09:46 pm
I would say the big difference between bifilar and twisted bifilar is better coupling and a better controllable transmission line impedance for the twisted bifilar case.
This thing is definitely a transmission line transformer using a very high mu core.

Useful information about transmission line transformers and their construction can be found in the "Transmission Line Transformers" Bible by Jerry Sevick.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Bud on July 11, 2018, 09:43:45 pm
It is not a transmission line transformer. You cant excite opposite ends of a transmission line and call it TLT just because you used a transmission line for it. 
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on July 11, 2018, 10:32:41 pm
It is not a transmission line transformer. You cant excite opposite ends of a transmission line and call it TLT just because you used a transmission line for it.

So then what is it? :-DD

Transmission lines are a superset of whatever you think "transformers" are; it's well worth learning, both for understanding their use, and creating their design. :)

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Bud on July 11, 2018, 10:51:37 pm
of course Tim it worth learning, so feel free to pick up ANY book on TL and start reading transmission line theory.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 12, 2018, 12:07:56 am
Who on earth can stop me doing exactly that ?
Whats wrong calling a transformer made from transmission lines a transmission line transformer, independent of the the circuit that it is embedded into ?
Confusing ...
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Floyo on July 12, 2018, 02:49:07 am
On the diy front there is some more info to be found here: http://www.eevblog.com/forum/projects/diy-injection-transformer-for-power-supply-control-loop-response-measurements/ (http://www.eevblog.com/forum/projects/diy-injection-transformer-for-power-supply-control-loop-response-measurements/)
There I attempted one version of an injection transformer, but this teardown made me try something more akin to the Omicron setup.

I took a magnetec M-012 Nanoperm core and wound around 50 turns of thin 50 ohm coax onto it, the "shield" is the primary, and the inner conductor the secondary. Attached are the measurements with the Analog discovery. Test were done with a 47 and 1K2 ohm load resistor on the secondary side. Drive impedance from the analog discovery wavegen was switched from 50 to "0" ohms, the latter increases the low frequency amplitude. Primary inductance is 72mH and pri-sec capacitance is 400pF. 

Results look quite ok for just slapping some turns on a core. Keep in mind that the power supply injection measurements are relative to the secondary, so absolute amplitude and phase of the transformer doesn't matter too much, if its decently well behaved.


Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DutchGert on July 12, 2018, 02:54:27 am
Hmm, am I the only one that is not impressed at all by the PCB layout job done?

The DC-DC convertors are done sloppy (big loops, small traces etc).
TH electrolitic caps everywhere, what about SMT MLCC's or Polymer jobbies?
Power is routed with thick traces, what about a nice solid power plane(s)?

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: dardosordi on July 12, 2018, 03:27:59 am
Im sure they regret not having potted the transformer now...
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: PA4TIM on July 12, 2018, 03:31:06 am
I just thinking, the output and input of the instrument are single ended and both connected to the same ground.  The transformer is balanced. I have no experience with this kind a measurements but if you use it to isolate the DUT from the analyser then you need two of them for 2 port measurements. One on the input and one on the output.
 I think you must connect it between two baluns to measure how it behaves for real isolation.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on July 12, 2018, 03:38:55 am
Im sure they regret not having potted the transformer now...


I doubt it....their customer base is probably very unlikely to bother making their own transformer. As much as I like to save money, spending a few days and at least a couple hundred $$ on failed attempts is a terrible way to 'save' $500.

For those looking for a bargain price, they were never going to be a viable customer anyway.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on July 12, 2018, 03:40:10 am
Im sure they regret not having potted the transformer now...


I doubt it....their customer base is probably very unlikely to bother making their own transformer. As much as I like to save money, spending a few days and at least a couple hundred $$ on failed attempts is a terrible way to 'save' $500.

Those looking for a bargain price were never going to be a viable customer anyway.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfram on July 12, 2018, 05:53:15 am
That's not ferrite and it's definitely not powdered iron, that's got to be nanocrystalline and nothing else. :)  Most likely Vacuumschmeltze, probably https://www.mouser.com/ProductDetail/Vacuumschmelze/T60006-L2040-W453?qs=sGAEpiMZZMs2JV%252bnT%2fvX8PvC43ppqs%252bksq4V5kp6Ay4%3d (https://www.mouser.com/ProductDetail/Vacuumschmelze/T60006-L2040-W453?qs=sGAEpiMZZMs2JV%252bnT%2fvX8PvC43ppqs%252bksq4V5kp6Ay4%3d) or similar.

  Oh s***t, it's blue! http://allegro.pl/rdzen-magnetec-m-083-rtn-40x25x15-nanoperm-i7430998721.html (http://allegro.pl/rdzen-magnetec-m-083-rtn-40x25x15-nanoperm-i7430998721.html) I don't know, I can't find the actual one, this looks like the closest, but still could work. I couldn't find a way to source the cores, always hard here in Argentina, if someone can source them would be cool to see some tests.

Never seen any in blue, I wonder if they got them as special order, or if there's another mfg I don't know about.  IIRC, it was just VAC and HMG (former Metglas) doing rapid-quench materials, but maybe there's new ones from China I don't know about?

Checking, I see very little on Ali Express, so probably not.


At PCIM this year, Tamura was presenting nanocrystalline CMCs, so they might also have the capability.

That's not ferrite and it's definitely not powdered iron, that's got to be nanocrystalline and nothing else. :)  Most likely Vacuumschmeltze, probably
That's for sure, the banner picture on the ones I posted had blue and brown cores, the ones I found for sale with the part numbers I was looking shown blue pictures but that's the only reference I got and I can't even read the web in that language!

I can confirm that the Vacuumschmelze nanocrystalline cores are the same color as the core in the EEVBlog video.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: AndersJ on July 12, 2018, 06:09:55 am
When the transformer secondary is connected to the DUT,
it will most likely cause a short circuit.

Why is there no coupling cap in the box?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfram on July 12, 2018, 06:14:40 am
When the transformer secondary is connected to the DUT,
it will most likely cause a short circuit.

Why is there no coupling cap in the box?

An injection transformer like this is not connected to the output of a power supply, it is inserted in series with the feedback loop (across a resistor). See the drawing in the user manual for clarification: https://www.omicron-lab.com/fileadmin/assets/Bode_100/Accessories/B-WIT_100/B-WIT-B-LFT-User-Manual-V1.1.pdf (https://www.omicron-lab.com/fileadmin/assets/Bode_100/Accessories/B-WIT_100/B-WIT-B-LFT-User-Manual-V1.1.pdf)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 12, 2018, 06:26:20 am
It goes into the cut open feedback loop, not parallel to the load. What you are thinking of is a current injector. The Omicron people also have those.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on July 12, 2018, 12:14:17 pm
I just thinking, the output and input of the instrument are single ended and both connected to the same ground.  The transformer is balanced. I have no experience with this kind a measurements but if you use it to isolate the DUT from the analyser then you need two of them for 2 port measurements. One on the input and one on the output.
 I think you must connect it between two baluns to measure how it behaves for real isolation.

Quite right, you only get good CMRR when the transformer is used in balanced operation, and the source and load are understood to have perfect CMRR.

Unbalanced, you get full capacitance (at medium frequencies, until it becomes obviously transmission line based in the HF limit).

The trick is to put a CMC on both sides of the transformer, to restore CMRR in the MF to HF limit.  Note that the CMC inductance resonates with the isolation capacitance, so it should be chosen (lossy material, or R+C in parallel) such that the resonance is well damped.  CMCs can be stacked (given the same consideration) to extend the CMRR arbitrarily.

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 12, 2018, 08:32:22 pm
Theoretically, this is all correct. In practice, I personally have never seen any documentation or video using two isolation transformers or common mode chokes.
Do you have a working example of this somewhere on the web ?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: JS on July 12, 2018, 11:25:24 pm
We have all we need to reverse engineer that transformer! Construction method, number of turns, impedance analysis, freq response... It's just matter of finding the right core material, with the impedance and number of turns permeability could be estimated... Would someone sell cores out of that material?

If you could sell a $100 unit with the same performance, you'd sell a truck load of them.
Would be interesting to try and duplicate their design and what performance it has with just some random core.
Forgot to answe this, it will result in a poor LF reaponse, depending on the core permeability, bassicaly the prinary inductance and the 50Ω makes a HPF which limits that, but even over that freq there is some distortion due to magnetization hysteresis which tapers off to the transformers higher freqs.

Please dave, when you find yourself on the lab with a screw driver and some length measurement device can you take a look at the core? To aim for a similar freq range that's kind of a big deal and I can't start making prototypes to shoot for one, sourcing those cores in Argentina is kind of tricky, as almost any component other than a 2n3904...

JS

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on July 13, 2018, 01:09:23 am
Theoretically, this is all correct. In practice, I personally have never seen any documentation or video using two isolation transformers or common mode chokes.
Do you have a working example of this somewhere on the web ?

In fact it is out there in the wild -- you're probably using it right now, though you may not have seen or noticed it!  Example: https://www.mouser.com/datasheet/2/336/H329-1199189.pdf (https://www.mouser.com/datasheet/2/336/H329-1199189.pdf)

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: envisionelec on July 13, 2018, 03:39:00 am
I reverse engineered the entire design and ran a cost analysis on a 10 piece basis.

The BOM cost is 110.84 including nominal labor/machining fees.

That's PTFE coated wire - 1USD a foot and there is about 24USD worth of wire on that core. I'll build one and characterize it.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on July 13, 2018, 03:43:51 am
I reverse engineered the entire design and ran a cost analysis on a 10 piece basis.

The BOM cost is 110.84 including nominal labor/machining fees.

That's PTFE coated wire - 1USD a foot and there is about 24USD worth of wire on that core. I'll build one and characterize it.

If that is correct.....the $500 price tag is a bargain for such a specialty/low volume piece of gear.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 13, 2018, 09:19:43 am
Well, I never saw them in a *measurement* application like Bode plotting or LF VNA. Any use there I missed ?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: JS on July 13, 2018, 10:01:43 am


I reverse engineered the entire design and ran a cost analysis on a 10 piece basis.

The BOM cost is 110.84 including nominal labor/machining fees.

That's PTFE coated wire - 1USD a foot and there is about 24USD worth of wire on that core. I'll build one and characterize it.

What tells you it's PTFE? I see some deformation of the insulatoe on the BNC solder, that shouldn't happen with PTFE...

For running small batches I could machine those my self and all labor so all that would come to my pocket but I'm trying to find the customs fees for importing the cores and then exporting the devices, that could ruin my budget to sell them at any reasonable price...

I intend to order a few cores to test and see what happens, worst case I end with an injection transforner for myself and a few nice cores for other applications, I probably will find them useful in audio, but before they arrive I could make some with any cheap core and look at the HF response where permeability doesn't play a big role. LF response will be anything but nice, I know that.

JS

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 13, 2018, 11:26:28 am
Of course you could try to reproduce the omicron injection transformer 1:1.

An alternative could be to use a stock ISDN or current transformer and to add a damping/compensation network to flatten out amplitude and phase response. Most swept generators have by far enough output for this approach, and the injected stimulus voltages are normally very small in order not to overdrive the DUT. When I tried this and if you apply the same criteria (5% phase error), results are not so vastly different from what omicron offers (e.g. 100Hz to a few 100kHz). The omicron claim of 1Hz to 10MHz is pure marketing; at band corners they are 15dB down and have phase errors of 70°. If you apply 1dB amplitude and 5°C phase error criteria, the range for them is ca. 50Hz to a few 100kHz (information from the datasheet of the B-WIT100). The big difference is that you have a 40dB power attenuation for the homebrew approach, which does not hurt at all in most cases.

https://electronicprojectsforfun.wordpress.com/injection-transformers/


Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on July 13, 2018, 11:45:44 am
The omicron claim of 1Hz to 10MHz is pure marketing; at band corners they are 15dB down and have phase errors of 70°.

They compensate in the box/software but print the spec on the box - making it look like is wider than anyone else would claim. Since it is a closed system, it's only sorta cheating.  :-DD
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 13, 2018, 11:58:35 am
I see it the same way, its marketing. Of course you can calibrate this out, but you could do the same with a homebrew probe. The homebrew has further advantages (4kV isolation voltage plus less capacitance). I wonder why Dave was so impressed by this transformer.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: JS on July 13, 2018, 12:14:51 pm
Of course you could try to reproduce the omicron injection transformer 1:1.

An alternative could be to use a stock ISDN or current transformer and to add a damping/compensation network to flatten out amplitude and phase response. Most swept generators have by far enough output for this approach, and the injected stimulus voltages are normally very small in order not to overdrive the DUT. When I tried this and if you apply the same criteria (5% phase error), results are not so vastly different from what omicron offers (e.g. 100Hz to a few 100kHz). The omicron claim of 1Hz to 10MHz is pure marketing; at band corners they are 15dB down and have phase errors of 70°. If you apply 1dB amplitude and 5°C phase error criteria
I like my phases in ºK, as ºC aren't absolute...
Quote
the range for them is ca. 50Hz to a few 100kHz (information from the datasheet of the B-WIT100). The big difference is that you have a 40dB power attenuation for the homebrew approach, which does not hurt at all in most cases.

https://electronicprojectsforfun.wordpress.com/injection-transformers/
One could also make a current amplifier and build a current transformer for the same freq range which might be easier, LF in current mode is much more forgiving than voltage mode, then terminate the transformer with the proper resistor and go from there. All that seems fine for the average lab, but this transformers exists for a reason, also, 1:1 transformer have better

This is from a transformer I've built some years ago for audio applications, source impedance was low, like 10Ω at most. The wiggle in the top end is due to the sound card I used, not coming from the transformer, I wander how it keeps going to a higher frequency, I only got the sound card at the time, so not much over 20kHz to work with at the time but I still have some of those at home, I'd only expect to get to a few tens kHz, is a big chunk of iron with a lot of turns, but I could wind a smaller one with less turns and better insulated wire to try.

I see it the same way, its marketing. Of course you can calibrate this out, but you could do the same with a homebrew probe. The homebrew has further advantages (4kV isolation voltage plus less capacitance). I wonder why Dave was so impressed by this transformer.
  It's specs aren't 1Hz to 10MHz, at least not in Dave's measurement, 5º was happening around 1.5MHz but at 1Hz was only 3º out. Test setup can influence on the measurement but his were at least as clean as you will get in a measurement setup. You don't need more than that, you need smooth transfer function without too much attenuation, as you can pick the reference from the output of the transformer, maybe a 3rd coil could be useful for that as it will reflect what the output is putting out better than the input coil and you wouldn't need a differential probe. In any case I wouldn't trust that what the generator is sending is the same as what the device is getting.

JS
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: chris_leyson on July 13, 2018, 12:28:51 pm
The core in the injection transformer is probably some nanocrystalline material as T3sl4co1l pointed out. It's got to be to get the high permiability required to get high magnetising inductance at low frequency. As it's a wideband transformer the low frequency limit is defined by the allowable peak flux density. From the data sheet fig. 5-2 they recommend a maximum drive level of 10dBm at 10Hz assuming a 10ohm injection resistor.
So, 10dBm is 0.707V RMS into 50 ohms or 1.414V RMS open circuit voltage at the generator output. Assume load resistance is 10 Ohms so that gives you 1.414*10/(50+10) or 235mV RMS across the primary. Peak flux density from the transformer equation is Bpeak(T) = Erms/(4.44 * f * N * Ae). N = 40, f = 10Hz, lets be generous and say Ae is 3cm2 = 3x10-4 m2 putting the numbers in gives about 440mT peak at 10Hz. Also in the data sheet they give peak flux density as a volt time product, 3.5E-3 Vs, assuming 3cm2 that gives a peak flux density of around 300mT. In calculating the RMS primary voltage I left out the primary magnetizing inductance and that would reduce the primary RMS voltage a little bit. It seems like quite a high working flux density, compared to ferrite anyway. It's only just about useable at 10Hz and I would say "usable at 1Hz" is pushing it a bit

Bifilar literally means "two filiaments" and it's two parallel wires bonded together, I've got a reel of it somewhere for winding coupling transformers on tiny binocular cores. Scientific wire company sell it https://www.scientificwire.com/acatalog/bifilar.html (https://www.scientificwire.com/acatalog/bifilar.html) The winding on the toroidal core is twisted to probably reduce the electric coupling between adjacent turns, MiniCircuits for example wind coupling and matching transformers using twisted wire.

Where are the mixers ? They're probably using analog switches, cheap, wide dynamic range and poor noise figure.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Kleinstein on July 13, 2018, 05:26:58 pm
The advantage of the nano-crystalline core material is that is can be used to higher flux levels than ferrites. So 400 mT would be no problem. When used in mains transformers some 800-1000 mT should be OK, saturation is around 1.1-1.2 T.

At low frequency the maximum power gets lower and the impedance gets lower. Still injecting 0.1 V might still be enough.

From the other tread (EEV-blog 1103):  Dave showed a picture with an AD834 that is likely used as the mixer.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: JS on July 13, 2018, 06:49:50 pm
So switches aren't used for the mixer, autocal, signal routing and filter managment I guess, there where a lot of them, I should take a look for the high res pictures!

JS

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 13, 2018, 08:33:58 pm
Of course you could try to reproduce the omicron injection transformer 1:1.

An alternative could be to use a stock ISDN or current transformer and to add a damping/compensation network to flatten out amplitude and phase response. Most swept generators have by far enough output for this approach, and the injected stimulus voltages are normally very small in order not to overdrive the DUT. When I tried this and if you apply the same criteria (5% phase error), results are not so vastly different from what omicron offers (e.g. 100Hz to a few 100kHz). The omicron claim of 1Hz to 10MHz is pure marketing; at band corners they are 15dB down and have phase errors of 70°. If you apply 1dB amplitude and 5°C phase error criteria
I like my phases in ºK, as ºC aren't absolute...

I agree :)

Quote
the range for them is ca. 50Hz to a few 100kHz (information from the datasheet of the B-WIT100). The big difference is that you have a 40dB power attenuation for the homebrew approach, which does not hurt at all in most cases.

https://electronicprojectsforfun.wordpress.com/injection-transformers/
One could also make a current amplifier and build a current transformer for the same freq range which might be easier, LF in current mode is much more forgiving than voltage mode, then terminate the transformer with the proper resistor and go from there. All that seems fine for the average lab, but this transformers exists for a reason, also, 1:1 transformer have better

 

This is from a transformer I've built some years ago for audio applications, source impedance was low, like 10Ω at most. The wiggle in the top end is due to the sound card I used, not coming from the transformer, I wander how it keeps going to a higher frequency, I only got the sound card at the time, so not much over 20kHz to work with at the time but I still have some of those at home, I'd only expect to get to a few tens kHz, is a big chunk of iron with a lot of turns, but I could wind a smaller one with less turns and better insulated wire to try.

For stability analysis I dont see a case where a 1:1 transformer is needed, because injected signal level is always very low in order to remain in the linear domain. I would be curious about a practical example of a 1:1 case :)

I see it the same way, its marketing. Of course you can calibrate this out, but you could do the same with a homebrew probe. The homebrew has further advantages (4kV isolation voltage plus less capacitance). I wonder why Dave was so impressed by this transformer.
  It's specs aren't 1Hz to 10MHz, at least not in Dave's measurement, 5º was happening around 1.5MHz but at 1Hz was only 3º out. Test setup can influence on the measurement but his were at least as clean as you will get in a measurement setup. You don't need more than that, you need smooth transfer function without too much attenuation, as you can pick the reference from the output of the transformer, maybe a 3rd coil could be useful for that as it will reflect what the output is putting out better than the input coil and you wouldn't need a differential probe. In any case I wouldn't trust that what the generator is sending is the same as what the device is getting.

JS
Still a big discrepancy to their own datasheet. I need to research this a little bit. I am afraid I need to get hold of a Keysight E5061B with LF option :)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: EEVblog on July 13, 2018, 09:13:46 pm
It looks like they take +/-40deg as the "frequency range" of the unit (i.e. 7Hz to 5MHz).
The 1Hz to 10MHz is the "usable range"
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: EEVblog on July 13, 2018, 09:14:53 pm
I wonder why Dave was so impressed by this transformer.

It's a heck of a lot better than some DIY ones I've used.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Hydron on July 13, 2018, 09:28:54 pm
Dave, could you quickly check the magnetising inductance of the isolation transformer? Would help with understanding what the low frequency performance is actually like.

If you wanted to go to town and play with the new toy then feel free to do a full set of measurements of the parasitics - the VNA (aka FRA) is great for this. Definitely agree that an instrument like this is very handy to have around - you'll keep finding uses for it.

Edit: Just found the SPICE model on their website - no need to measure it unless you want to compare specs to reality.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: bitwelder on July 13, 2018, 09:58:56 pm
(https://i.imgur.com/ZSz9Y7Q.png)

For 5K I'd hoped Omicron' virgins would have taken care to align those relays a little better.  :D
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 13, 2018, 10:53:22 pm
@Dave

Why didnt you use a matching network to straighten things out ?

BTW: In about 2 months Im getting my hands on a Keysight E5061B-3L5 (5Hz to 3GHz) VNA with impedance measurement option.
Then I can repeat my measurements, and I will publish them as usual.

regards
  Wolfgang
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 13, 2018, 11:50:39 pm
Omicrons nude virgins definitely work in the software department :)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: envisionelec on July 13, 2018, 11:59:55 pm


I reverse engineered the entire design and ran a cost analysis on a 10 piece basis.

The BOM cost is 110.84 including nominal labor/machining fees.

That's PTFE coated wire - 1USD a foot and there is about 24USD worth of wire on that core. I'll build one and characterize it.

What tells you it's PTFE? I see some deformation of the insulatoe on the BNC solder, that shouldn't happen with PTFE...

For running small batches I could machine those my self and all labor so all that would come to my pocket but I'm trying to find the customs fees for importing the cores and then exporting the devices, that could ruin my budget to sell them at any reasonable price...

I intend to order a few cores to test and see what happens, worst case I end with an injection transforner for myself and a few nice cores for other applications, I probably will find them useful in audio, but before they arrive I could make some with any cheap core and look at the HF response where permeability doesn't play a big role. LF response will be anything but nice, I know that.

JS

The pattern of deformation is exactly what PTFE looks like when its heated. Soldering that center pin takes a lot of heat...

The core isn't anything special either. I'd be willing to bet it's a bog standard iron powder T184-2. Just a hunch. ;)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Floyo on July 14, 2018, 04:47:01 am
It cant be that T184-2 core, the AL is way too low to get the specified inductance. My bet goes out to a Vacuumschmelze W424, the colour matches, the size matches, as do the specs if you run the numbers. I knew I had one of those laying around somewhere, so I dug it up and whipped up another test. This time 50 turns (I had some wire leftover after 40 ;)) on the W424 core, the picture speaks for itself.

Once again I measured with the analog discovery. The "Cal" image shows  the wavegen output connected to both CH1 and CH2.
CH2 is displayed in blue and is in relative mode, so gain and phase relative to channel one. This removes any gain variations due to wavegen output loading etc (its a 50 ohm output).

"Abs" shows the measurement as Omicron does it, I think, Here the amplitude is absolute compared to the wavegen (and thus -6db because of the 50Ohm termination), and the phase is relative to CH1.
"Rel" is the same measurement, but now in relative mode, this shows the transfer function of just the transformer.
"100mV" is the previous absolute measurement but now at 100mV instead of 1V input amplitude, this lessens the loading on the wavegen output stage.

Pri -sec capacitance is 130pF
Magnetizing inductance is 274mH
And leakage inductance is 3uH
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on July 14, 2018, 05:07:16 am
What influence does the twist pitch of the wire have on performance?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on July 14, 2018, 05:19:46 am
It changes the characteristic impedance of the transmission line. Depending on twists/m, the impedance will be around 100Ohms, with more twists making the impedance lower.
Its not extra simple, because wire diameter and dielectric used also play a role.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Floyo on July 14, 2018, 05:33:52 am
How about using coax, it has already been tuned to be a good 50 ohm transmission line. And how about impedance matching from primary to secondary, and/or the transmission line impedance.

For practical measurements on power supplies etc 1-2 Mhz should be plenty of bandwidth. I have never seen anything that comes close to those bandwidths, but you never know :)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: GigaJoe on July 14, 2018, 05:56:02 am
it seems close , Vitroperm 500 F , Vacuumschmelze
https://www.mouser.com/pdfdocs/VACChokesandCoresDatasheet.pdf (https://www.mouser.com/pdfdocs/VACChokesandCoresDatasheet.pdf)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Hydron on July 14, 2018, 09:02:40 am
Damn, just went to post my DIY effort and found I'd been beaten to it!

I too used a nanocrystaline core, this one scavenged from a Wurth 3-ph CM choke:
https://katalog.we-online.com/pbs/datasheet/744839047160.pdf
Looks to be a little bigger than the one linked earlier, and encapsulated inside a plastic shell (I removed the protrusions in the pic before winding it).

Made a twisted pair with a drill and some random hookup wire and put 40 turns on it, as this coincidentally both matched the original number and also gave the same magnetising inductance as the SPICE model of the original indicated (actually 39 would have been the correct number in restrospect).

Took maybe an hour all up to build (not including measurements) and gave:
Xm = 222mH
Xl (per winding) = 1.25uH
Cpri-sec = 140pF

Unfortunately I couldn't do the whole sweep from 1Hz-10MHz in one hit, so there are four graphs here (corresponding to Floyo's "abs" and "rel" measurements - filenames should be descriptive enough of what's being measured).

While the low-freq performance of mine is slightly better, it only makes it to ~7MHz before falling apart. Possibly because I wound it while clothed, and don't fulfil the other two criteria either?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: JS on July 14, 2018, 02:11:48 pm
Damn, just went to post my DIY effort and found I'd been beaten to it!

I too used a nanocrystaline core, this one scavenged from a Wurth 3-ph CM choke:
https://katalog.we-online.com/pbs/datasheet/744839047160.pdf
Looks to be a little bigger than the one linked earlier, and encapsulated inside a plastic shell (I removed the protrusions in the pic before winding it).

Made a twisted pair with a drill and some random hookup wire and put 40 turns on it, as this coincidentally both matched the original number and also gave the same magnetising inductance as the SPICE model of the original indicated (actually 39 would have been the correct number in restrospect).

Took maybe an hour all up to build (not including measurements) and gave:
Xm = 222mH
Xl (per winding) = 1.25uH
Cpri-sec = 140pF

Unfortunately I couldn't do the whole sweep from 1Hz-10MHz in one hit, so there are four graphs here (corresponding to Floyo's "abs" and "rel" measurements - filenames should be descriptive enough of what's being measured).

While the low-freq performance of mine is slightly better, it only makes it to ~7MHz before falling apart. Possibly because I wound it while clothed, and don't fulfil the other two criteria either?
Nice attempt, I like the response, being bigger might give you the good LF response. The plastic shell leaves the wire further away from the core, making a worse coupling thus higher leakage inductance which could affect the HF inductance. Also, the non PTFE wire would affect HF performance, I guess one or both of those are giving you the differences. You could try twisting the wires a bit more or building a thiner shell for the core (like some tape to keep it together and not damage the wire insulator) if you are after a better HF response.

I'd love to have some cores to play around with!

JS
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: chris_leyson on July 14, 2018, 04:53:01 pm
Big thanks to Tim for the heads up on Vacuumschmelze nanocrystaline material. T60006-L2040-W424 looks like the core they use, it's got the right Al value. Thanks to Floyo and Hydron for winding some test transformers and providing test results.
I wonder, did Omicron try 2:1 and 3:1 transformer ratios if they are injecting voltage into a 10 Ohm load. Why would you pick 10 Ohms and not 50 Ohms for a load anyway, it doesn't make any sense. Twisted trifilar or quadrifilar wound would give you the impedance match either side of 10 Ohms and also drop the LF corner. Not sure how that would effect the HF corner, will have to try it out. Nice 1:1 wideband transformer, no magic voodo involved and overpriced for what it is. More marketing than practical engineering.
Anyways, thanks Tim for the heads up on the material, it's not cheap and won't compete with ferrite in terms of price but for wideband transformers it has potential, all depends on the HF losses.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on July 14, 2018, 06:10:13 pm
Cheers. :)

Note that you can use ferrite just fine, but you'll lose a couple octaves at the low end.  You can find materials with mu_r up to about 20k, with >8k being typical for hi-mu types.

The mid-band (i.e., magnetizing) impedance also isn't as high, but this isn't relevant at these impedances.  It's quite useful for CMCs, hence the application of nanocrystalline material there as well.

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Hydron on July 14, 2018, 06:56:39 pm
I took some 50 ohm load measurements at the same time if they are of interest - see attachments.

As for PTFE vs PVC wire, I didn't have any of the former, though I could butcher an Ethernet cable for a pair of something which I assume is not very lossy. Would it really make a major difference at <10MHz? Throwing my measured lumped parameters into SPICE gives reasonable correlation to the measurements (biggest outlier is that the resonance point in SPICE is a little higher - more like 8.5MHz than ~7MHz).

There are also some other things I could do to improve matters if I ever needed to use this in anger up near the top of it's range - a few less turns, shorter lead-in wires etc etc. No real need though, this was mainly done for the challenge (wasn't much of one given the right core material) and I already have an isolated sig-gen for my Cleverscope which lets you do the PSU loop measurements from <1Hz up to 65MHz with no magnetics required.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on July 24, 2018, 06:13:24 am
Building a transmission line transformer like this appears quite a challenge ...

Anyway, here's my results (using random cores from the junk box, didn't record the µH/n² values):

The ugly, a rather bulky ferrite core and thin litz wire (about 5m wire length)
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=482426;image)

Works (-3dB) from 81Hz to 3.4MHz
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=482444;image)

Next try, a core used as an EMC suppressor (just a multi-strand cable fed through it), and Wire-Wrap (ca. 3m)
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=482432;image)

-3dB from 117Hz to 11Mhz
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=482450;image)

A core scavenged from an EMC common mode choke (VAC / Sekels branded, rather small), used less than 2m twisted pair from a CAT5e ethernet cable
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=482438;image)

-3dB from 48hz to 14Mhz
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=482456;image)

Now I'm searching for a somewhat larger core of the last kind (probably micro-crystalline, as it is from VAC/Sekels) to give it another try and reach lower frequencies. The length of the twisted pair clearly defines the upper limit, simply verified by measuring a length of twisted pair before winding it onto the core.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Kleinstein on July 24, 2018, 07:05:17 am
There are 2 effects limiting the usefulness at low frequency:
1) core saturation, which is amplitude (voltage) dependent
2) the inductance and thus impedance, which would depend also on the source / load impedance

With the high Al ferrite cores, it can be important to keep the mechanical stress from the windings low (e.g. add so foam). Stress can lower the AL value quite a lot.

The nano-crystalline material, has low magnetostriction and is thus less sensitive to stress.

Magnetostriction also causes another effect (ferro-resonance):
 there can be a rather narrow mechanical resonances (high Q, maybe 1000) that can also act back on the electric parameters. Due to the small width it could be easily overlooked. For high quality it might help to have some soft (e.g. wax) potting of the transformer / winding to dampen the resonances.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: halexa on July 24, 2018, 07:08:03 am
Why is there no ground fill ont that main PCB?

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on July 24, 2018, 08:14:00 am
Building a transmission line transformer like this appears quite a challenge ...

Anyway, here's my results (using random cores from the junk box, didn't record the µH/n² values):
-3dB from 48hz to 14Mhz

I would be rather happy with that one in many applications.

Is that a 3577A you used for the test?

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: thm_w on July 24, 2018, 09:00:08 am
Why is there no ground fill ont that main PCB?

You'd have to ask the designer. But there would be at least a few inner planes (4+ layer PCB), used for power and ground.
So strictly there is no need for a top layer ground fill, but could reduce EMI slightly if it were used.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on July 24, 2018, 03:37:33 pm
Anyway, here's my results (using random cores from the junk box, didn't record the µH/n² values):
-3dB from 48hz to 14Mhz
I would be rather happy with that one in many applications.
It's easy to build, I'll try to find the original part number of the core / EMC choke, and I'm going to look for more cores / chokes when I have some spare time, visiting the various junk boxes (including the new  stock, that isn't junk at all).
Quote
Is that a 3577A you used for the test?
Yes, it is mine. Located in my home lab, we don't have such fancy stuff at work, but quite a variety of EMC chokes ...

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on July 24, 2018, 10:03:15 pm
Just for the record, the core I've used for the third transformer is most probably the Vacuumschmelze T60006-L2030-W423, this is the nearest match. The common mode choke that I scavenged that core from is a T60405-R6166-X018-80. Didn't find any more interesting cores for more experiments. Can't beat the mentioned T60006-L2040-W424 with any of the cores that I've found.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on July 25, 2018, 02:30:42 am
Is that a 3577A you used for the test?
Yes, it is mine. Located in my home lab, we don't have such fancy stuff at work, but quite a variety of EMC chokes ...

For this thread - I was setting up to do some tests with the same 3577A network analyzer unit. The PSU has some issues and it finally would not power up at all. I believe I have located the problem and parts are on the way. Hopefully, if the failed PSU did not fry the rest of the system, I can do a few tests as well.

I have 3 DC-DC converters on the design table and would really like to improve my ability to analyze loop stability.

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on July 26, 2018, 12:21:07 am
All this good transformer work really should be moved to its own thread in an appropriate forum...
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on July 26, 2018, 04:55:50 am
Made another two transformers using that salvaged VAC core. Used bifilar (non-twisted) winding, PTFE isolated.

Results

1st one made with one layer of turns, resulting in about 30 turns, the core has 62µH/n²
-3dB response is from 71Hz to 14MHz, one can see about 0.2dB transmission loss.
The former one that was wound using twisted pair from ethernet cable has near zero losses, so I believe these losses are due to the wire's resistance.
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=483731;image)
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=483755)

2nd one made with two layers of turns, about four times the magnetizing inductance, resulting in
-3dB response from 19Hz to 8.4MHz, somewhat more loss, maybe 0.3dB. It's not exactly a fourth of the 1st ones LF response, this is because I cut the wire somewhat too short, wasn't enough for 60 turns.
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=483719;image)
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=483761)


And now for something completely different:
I've connected them to the TDR to measure the wire length and see the transmission line's impedance:
Todays 1st one:
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=483737)

Todays 2nd:
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=483725;image)

And for comparison, this one from last week to point out the difference between bifilar and twisted pair winding:
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=483743;image)
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=483749;image)


One can clearly see, the impedance over wire length is flatter for the twisted pair, but it appears to have none or very little effect on the frequency response.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on July 28, 2018, 11:12:58 am
Made another two transformers using that salvaged VAC core. Used bifilar (non-twisted) winding, PTFE isolated.

Results

I just got my 3577A repaired.....just trying to figure how it works now. So far, I have not actually used it.......

I have some transformers and parts to take a shot at this but need to make sure I am setting up the test correctly.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on July 28, 2018, 05:19:17 pm
I've made these measurements with the transformer terminated by the 50Ohm input. Switching the input to high impedance and using an 10Ohm resistor to terminate the transformer gives different results. The low -3dB is shifted down to below 10Hz with the second transformer, the upper end -3dB gets about 7MHz.

Don't forget to normalize the 3577A (with no transformer, but termination as wanted). I've used log sweep from 5Hz to 20Mhz , 120s (or 60s) sweep time and 1Hz RBW, auto RBW off.

I've made this simple test rig, the switches are used to bypass the DUT, one can see the 10Ohm termination resistor placed into the pin sockets. The upper left SMB connector isn't used for anything, just in case you wonder.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on July 30, 2018, 12:17:31 pm
Hello, 

My first post here.

California is on fire, when the smoke clears I will test this thing.

The VAC T60006-L2030-W514-03- core appears to be an exact match for size and color for the core in the real B-Wit injection transformer.

https://www.mouser.com/datasheet/2/599/W514-238036.pdf (https://www.mouser.com/datasheet/2/599/W514-238036.pdf)

See the attached photo of the real deal side by side with a home rolled version. The home rolled version has 40 turns of twisted pair CAT 6 plenum wire.

Thanks DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Hydron on July 30, 2018, 07:11:34 pm
Nice, looks like the closest match yet (physically at least)!

Seems that Dave's "Nude Austrian virgins" line suckered a bunch of us into proving him wrong :P To be fair it is a relatively exotic core material.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 02, 2018, 02:56:11 am
I thought it might be useful context to show what 50-Ohm isolation xfrms are available on the used market for relatively little money.

Here are the plots of two North Hills 50-Ohm Isolation Transformers, models 0016 PA and 0017 CC. They have been around for more than 20 years, and the latter has been on HP/Agilent's recommended list for about that long. I don't know why HP never mentioned the 0016, because its the better. These measurements are made with 50 Ohm source and termination, into 1M inputs. The Anritsu VNA only goes down to 10Hz so a separate measurement was made down to 1Hz.

As you can see, both units have very good LF extension, less than -3dB down @ 1 Hz. Reducing the source impedance extends it further. On the high end, the 0016 is -3dB at about 24MHz and the 0017 to 7.5MHz. Response shape above a few MHz is greatly impacted by analyzer input and cable reactances. Best plan is to terminate the xfmr right at the secondary output.

These things generally go for 30-60 bucks when they show up on eBay.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on August 02, 2018, 01:55:22 pm
Hello,

Went out through the wild fire smoke to the shop.

I tested both the real B-WIT injection transformer and the Home-Roll.

Pretty much Same Same.

Thanks DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 02, 2018, 02:04:39 pm
Thanks for posting this. Not much different from the NH 0016 tested above.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: ace1903 on August 02, 2018, 07:15:18 pm
There is cheap source of vitroperm cores in RCD switches. I took one from hardware store for ~10eur.
Obviously it is smaller when compared with "original"  one. Don't know if 300mA has bigger core.
Anyone interested to make measurement and compare results?
I have LCR meter but don't have network analyser.   
Attached picture of RCD Commel 470-025 with core opened from protective plastic.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 02, 2018, 07:58:41 pm
You could measure the inductance of one turn.
This value should be larger than 60uH to make the core interesting, I've also had tested some cores with 20uH / n^2, they didn't give satisfactory results (too many turns required for the low frequency rolloff, killing the high frequency response).

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: ace1903 on August 02, 2018, 08:48:43 pm
Measured with Voltcraft LCR-300 single turn:
88uH at 100Hz Q2.62
87uH at 120Hz Q 2.92
79uH at 1kHz Q4.62
46.6uH at 10kHz Q1.642
8.46uH at 100kHz Q0.668

Is this drop at 100kHz expected? I mostly do embedded programming and digital electronics and I maybe did some error during measurement( with 8 turns results are similar with more drastic drop).
I also own Analog Discovery 1 and probably can do some kind of transfer characteristic measurement but I lack knowable how to make measurement set up.
Where to put resistors and with which value?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 02, 2018, 11:31:13 pm
Yes, that drop in inductance is to be expected for that kind of core.
If you manage to apply 40 ... 50 turns of twisted pair or bifilar as done before here in this thread, I'd expect a pretty low frequency limit for it. Upper limit depends on the length of wire, try not to get longer than 2 ... 3 meter.

So, now take the wires of same colour as input / output of this transformer, you should measure (number of turns)^2 * 79uH @ 1kHz as the magnetizing inductance at either input and output. Short output and measure the inductance of input, you get the stray inductance, that should be pretty low for this construction.

Next apply a function generator at the input, connect a 10 Ohm resistor across the output and measure voltage across that output. Sweep frequency from 1Hz (or whatever is lowest possible) to 20Mhz at a rather low level (< 1Vpp) and draw the frequency response (bode plot). This should get similar results to the posted plots. This measurement includes the loading of the transformer / 10R to the generators output and differs from the transformers response. For an advanced measurement, apply the same generator to the input, keep the 10R termination and measure both voltages (input and output) at the same time, then calculate their ratio - this gives the transformers response alone. I'm not familiar with the Analog Discoveries possibilities, it should offer some kind of Bode Plot feature with two input voltages and one generator output, this is what you want.


Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 02, 2018, 11:53:09 pm
Next apply a function generator at the input, connect a 10 Ohm resistor across the output and measure voltage across that output. Sweep frequency from 1Hz (or whatever is lowest possible) to 20Mhz at a rather low level (< 1Vpp) and draw the frequency response (bode plot). This should get similar results to the posted plots. This measurement includes the loading of the transformer / 10R to the generators output and differs from the transformers response.

Why the 10R? Does that reflect how you most often use them?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 03, 2018, 12:12:59 am
Next apply a function generator at the input, connect a 10 Ohm resistor across the output and measure voltage across that output. Sweep frequency from 1Hz (or whatever is lowest possible) to 20Mhz at a rather low level (< 1Vpp) and draw the frequency response (bode plot). This should get similar results to the posted plots. This measurement includes the loading of the transformer / 10R to the generators output and differs from the transformers response.

Why the 10R? Does that reflect how you most often use them?


10R is the value the Omicron transformer is specified for (recommended 1R ,,, 10R afair). Just to be comparable - e.g. I did the measurements for my home rolled transformer with 50R termination and get different results.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on August 03, 2018, 12:20:03 am
Yes, skin effect dominates by ~20kHz or so, at which point the core resembles a Warburg element.

Example:

(https://www.seventransistorlabs.com/Images/CurveFit1.png)

Approximate equivalent circuit:

(https://www.seventransistorlabs.com/Images/CurveFit2.png)

An upside to this for EMC purposes: the Q is very low as the impedance rises towards peak, so that you can pair the CMC with a modest capacitance and not worry about resonance.  Because the mu, going into this region, starts higher than it is for ferrite, and hi-mu ferrite drops off (~single pole) at a roughly similar frequency (usually ~100kHz, but depends on core size), nanocrystalline has a wider and taller impedance peak than ferrite does, making it just that bit better.

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Bud on August 03, 2018, 12:36:03 am
Quote
Why the 10R? Does that reflect how you most often use them?
Quote
10R is the value the Omicron transformer is specified for (recommended 1R ,,, 10R afair). Just to be comparable - e.g. I did the measurements for my home rolled transformer with 50R termination and get different results.

Low value load impedance Because of the way injection transformers are used. To inject the signal into the power supply control loop you break the control loop connection and insert a low value resistor in it in series across which you then connect the injection transformer. Resistor values up to 10 Ohm seem to be reasonable to not have effect or have minimal effect on the control loop under test. 50 Ohm may be too high, i'd shoot for and test with 10 Ohm.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 03, 2018, 12:54:25 am
Quote
Why the 10R? Does that reflect how you most often use them?
Quote
10R is the value the Omicron transformer is specified for (recommended 1R ,,, 10R afair). Just to be comparable - e.g. I did the measurements for my home rolled transformer with 50R termination and get different results.

Low value load impedance Because of the way injection transformers are used. To inject the signal into the power supply control loop you break the control loop connection and insert a low value resistor in it in series across which you then connect the injection transformer. Resistor values up to 10 Ohm seem to be reasonable to not have effect or have minimal effect on the control loop under test. 50 Ohm may be too high, i'd shoot for and test with 10 Ohm.

OK, got it. I've not done it myself, but most of the R's I've seen used for control loop repose were higher than 10R, more like 33-50.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Hydron on August 03, 2018, 01:06:47 am
50R seems reasonable unless the feedback divider values are unusually low. When I've done this type of testing (using a video isolation transformer, as I did not have my isolated sig-gen available) 50R worked well. The actual value will not be critical as long as it's reasonable.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on August 03, 2018, 01:27:28 am
Another reason to use a very low termination resistor for an injection transformer is bandwidth. The lower the termination resistor, the higher the bandwidth.
Another trick to increase bandwidth in an injection transformer is a (lossy) matching network at the primary side. This damps out resonances and flattens frequency response.  :)

Enhanced by these tricks, even very normal off-the-shelf signal transformers can be successfully used up to a few 100kHz.
The loss is normally no problem because the injected signal needs to have a very low amplitude.

https://electronicprojectsforfun.wordpress.com/injection-transformers/

shows some of these.



Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 03, 2018, 01:33:37 am
Another reason to use a very low termination resistor for an injection transformer is bandwidth. The lower the termination resistor, the higher the bandwidth

Hmmm... I see exactly the opposite. I'll post some results later.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on August 03, 2018, 04:34:49 am
Hello,

For grins this is a plot of the Jensen ISO-MAX VB-1BB 75 Ohm isolation transformer on ebay for $20. Not bad for $20, if price is the object.

The second plot is the Home-Roll. Can't tell it from the B-WIT.

Both plots 401 test points from 1Hz to 25MHz

Thanks DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on August 03, 2018, 05:16:57 am
I have the same Jensen ISO-MAX.... seems like a great bang for your buck.

Short and misplld from my mobile......

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 03, 2018, 01:12:42 pm
Another reason to use a very low termination resistor for an injection transformer is bandwidth. The lower the termination resistor, the higher the bandwidth.

Here's the NH 0016PA transformer with 50 Ohm source and 1 terminated with 50, 10, and 1 Ohm. Bandwidth goes from >20MHz @ 50 Ohms to ~150kHz @ 1 Ohm. This is pretty typical of the better 1:1 xfmrs I've looked at. You can get a little of the bandwidth back with lower source R.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on August 03, 2018, 03:07:58 pm
Hello,

All this talk of termination resistors.

Is this with a resistor intentionally placed across the secondary winding plus the resistance to ground internal to the VNA?

That means that we have the external resistor across the secondary coil in parallel with the instrument internal resistor to ground.

Different related topic.

It is not so much about adding additional resistance to extend or reduce bandwidth it is about resistance being used to tune or critically dampen the native inductance of the coil. Another way to think of it goes like this. Inductance is often added to RF circuit to increase Q and extend bandwidth with inductive peaking. 
 
Thanks DT   
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: JS on August 03, 2018, 06:48:37 pm
Hello,

All this talk of termination resistors.

Is this with a resistor intentionally placed across the secondary winding plus the resistance to ground internal to the VNA?

That means that we have the external resistor across the secondary coil in parallel with the instrument internal resistor to ground.

Different related topic.

It is not so much about adding additional resistance to extend or reduce bandwidth it is about resistance being used to tune or critically dampen the native inductance of the coil. Another way to think of it goes like this. Inductance is often added to RF circuit to increase Q and extend bandwidth with inductive peaking. 
 
Thanks DT
The resistor is added because you want low resistance to use the transformer, so you want to know the response of the transformer in its intended way. You want such resistance to reduce the impact of the insertion of the transformer onto the DUT.

JS

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on August 03, 2018, 07:09:11 pm
What about also *driving* the transformer from a very low impedance !

Its the old rule of thumb: The lower 3dB corner sits where inductive impedance is ca. 4 times the feeding and terminating impedances.
So, when the feeding impedance is just a few ohms and the inductance stays the same, the low frequency corner is improved.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 03, 2018, 10:53:21 pm
All this talk of termination resistors.
Is this with a resistor intentionally placed across the secondary winding plus the resistance to ground internal to the VNA?

Yes. But the VNA Rterm is usually set to 1MegOhm for these measurements.

Quote
That means that we have the external resistor across the secondary coil in parallel with the instrument internal resistor to ground.

Yes, but its not always actually present in use. It depends on what you're using the transformer for, and what the load presented to it is..

Quote
It is not so much about adding additional resistance to extend or reduce bandwidth it is about resistance being used to tune or critically dampen the native inductance of the coil.

That works really well if the circuit on the secondary side is fixed, and you can tailor it to the xfmr. I used to do that when designing transformer-coupled mic preamps, optimizing the xfmr RC termination for flattest input impedance and/or freq response. (Deane Jensen was a mentor of mine, and showed us all how to do this back in the 80's.)

But this RC compensation doesn't work when the circuit on the secondary side is an unknown load which you're injecting a signal into. That load is in parallel to whatever Rterm (if any) is across the 2ndary. In that case we want no termination resistor, but we need to deliberately terminate the xfmr with a range of loads it will encounter to see how its characteristics change.

Here's an example, a circuit HP used to recommend for their VNA's to measure output impedance of DC voltage regulators. This is an easy circuit to use with VNAs because of the 1 Ohm current multiplier. Using short and load compensation, I get good results with it down to 10mOhm or better.

The transformer they recommended was the North Hills 0017CC, shown earlier in this thread, a 50 Ohm 1:1 unit rated at 5MHz BW (7.5MHz actual). In this circuit the xfmr is operating at load impedance of (1 Ohm + Zdut) at each freq. At those loads the xfmr bandwidth is varying dramatically with load Z. The useable bandwidth of the 0017CC at 1 Ohm is less than 100kHz (more like 10kHz if you want to measure phase accurately, see the plots a couple posts up for the similar 0016PA). And that's why HP's Z plots for this technique only go to 100kHz, even with the 500MHz analyzer. The xfmr bandwidth into 1 Ohm is the limiting factor.

Hope this helps.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 03, 2018, 10:56:13 pm
What about also *driving* the transformer from a very low impedance !

Yes, it extends the bandwidth some, but my VNAs all have 50 Ohm outputs, so an external amplifier with direct-coupled output is required to do it.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on August 03, 2018, 11:21:33 pm
I did it the primitive way and I added a voltage divider with 50 Ohms impedance for the generator and only a few Ohms to drive the transformer.
Loss is welcome because levels should be very low and it also dampens out resonances.

See here:

https://electronicprojectsforfun.wordpress.com/injection-transformers/
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 03, 2018, 11:41:39 pm
I did it the primitive way and I added a voltage divider with 50 Ohms impedance for the generator and only a few Ohms to drive the transformer.
Loss is welcome because levels should be very low and it also dampens out resonances.

For control loop response, that works, since you need only small injection signal. How high are you trying to measure? Most ones I've seen only look at 100kHz and below.

Quote
See here:
https://electronicprojectsforfun.wordpress.com/injection-transformers/

Yes, I've seen that, it is relevant for control-loop-response but not for using a xfmr for output isolation (breaking ground loops for low-level measurements, aka "braid error").
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on August 03, 2018, 11:52:53 pm
Hi,

my measurement go up to a few 100kHz only. They are mostly for linear power supply for measurement circuits where low noise is an issue (like preamps for noise measurements, ...). Funny enough, even battery powered supplies have noise peaks.

For the "braid error" issue I am working on another approach injecting current and measuring voltage response of a PSU. In these cases I do not need a transformer,
but an active injector, the same ideas like the PicoTest ones. Stability can then be inferred by extracting data from the Nyquist plot of the output impedance.

This is work in progress, but in September I can get my hands on a Keysight E5061B-3L5 (VNA from 5Hz to 3GHz), and then I can properly measure all my homebrew stuff without improvisation.

There are nice appnotes from Keysight how a VNA can be used to measure milliohm impedances in PDN networks. I learned a lot from those.

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Kleinstein on August 03, 2018, 11:58:00 pm
What about also *driving* the transformer from a very low impedance !

Yes, it extends the bandwidth some, but my VNAs all have 50 Ohm outputs, so an external amplifier with direct-coupled output is required to do it.

If there is no need for high power, one could use a simple shunt resistor at the input side of the transformer. Even with a 50 Ohms output it lowers the impedance, but also the amplitude. If needed (e.g. longer cables) one could add series resistance to get back 50 Ohms impedance for matching.

For the normal use, one would also measure the transfer characteristics of the transformer. So the measurements could be done beyond the 3 dB point. With a not so large load resistance an the secondary side the extra loading by the circuit should not have that much effect. With correction it's no so much die transfer function that matters, but how stable this function is.

Besides the forward transfer function, one might have to care about the coupling capacitance. If the point where the injection transformer is used is high impedance, this is likely the more important limitation. So in a power supply the transformer should go right between the output and the divider - the point between the divider and the FB amplifier would be more like bad choice, as it is high impedance and a few 100 pF can really make a difference.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 04, 2018, 12:12:25 am
my measurement go up to a few 100kHz only. They are mostly for linear power supply for measurement circuits where low noise is an issue (like preamps for noise measurements, ...).

Most of these xfmrs will work for you, then.

Quote
For the "braid error" issue I am working on another approach injecting current and measuring voltage response of a PSU. In these cases I do not need a transformer,
but an active injector, the same ideas like the PicoTest ones. Stability can then be inferred by extracting data from the Nyquist plot of the output impedance.

This is work in progress, but in September I can get my hands on a Keysight E5061B-3L5 (VNA from 5Hz to 3GHz), and then I can properly measure all my homebrew stuff without improvisation.

I look forward to seeing your results!

Quote
There are nice appnotes from Keysight how a VNA can be used to measure milliohm impedances in PDN networks. I learned a lot from those.

Agreed. The "shunt-thru" technique can give good results into higher freqs.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on August 04, 2018, 03:22:27 am
Hello,

Now that the conversation regarding the termination resistor is near complete take a look at page 8 figure 4.1 of the Omicron Lab injection transformer manual. The recommended injection resistor value is between 1R and 10R.

https://www.omicron-lab.com/fileadmin/assets/Bode_100/Accessories/B-WIT_100/B-WIT-B-LFT-User-Manual-V1.1.pdf (https://www.omicron-lab.com/fileadmin/assets/Bode_100/Accessories/B-WIT_100/B-WIT-B-LFT-User-Manual-V1.1.pdf)

Now looking at injection transformer phase measurements:

The transformer phase plot shows the phase difference between the transformer primary and secondary. Some folks here say that the injection transformer is no longer useful when phase exceeds some value plucked from the chart. This needs a closer look.

If you look at the Signature Bode 100 gain vs Phase Margin chart, the point where gain is equal to 0dB the PM gives a very good indication of power supply stability. Doesn’t the injection transformer phase effect the PM of the power supply? The short answer is no. 

Thanks DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 04, 2018, 06:55:55 am
Now that the conversation regarding the termination resistor is near complete take a look at page 8 figure 4.1 of the Omicron Lab injection transformer manual. The recommended injection resistor value is between 1R and 10R.

More precisely, it can be used with R's from 1R to 10R, with 10R recommended.

Quote
If you look at the Signature Bode 100 gain vs Phase Margin chart, the point where gain is equal to 0dB the PM gives a very good indication of power supply stability. Doesn’t the injection transformer phase effect the PM of the power supply? The short answer is no. 

Well of course not. That isn't the question. The question has to do with the accuracy of the measurement.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on August 04, 2018, 09:53:18 pm
If you want infinite bandwidth from such a transformer, and don't mind a flat 6dB insertion loss: split the transmission line in the middle, and add terminations here.  You need an R+C across the (now open) ends of these windings, where:
R = Zo
C >= 2.5 * k * (377Ω) * t_half / Zo^2

k = effective dielectric constant (note this is less than the material k itself, when the dielectric is mixed, e.g., microstrip, twisted pair, foam, etc.)
t_half = transmission line electrical length (units of time)

This terminates the half-windings, so the transformer looks like a pair of Zo resistors from P1 to S1 and from P2 to S2.  Obviously, this breaks transformer action.

One might rightfully note this isn't a transformer at all anymore, and the circuit can be greatly simplified by removing the transformer altogether; now you have coupling capacitors (the termination resistors are completely optional, unless you liked the insertion loss), and the CMRR is still just as bad, although it's bad at low frequencies too (oh well? :P ).

To restore transformer action, connect across the cut ends (primary middle to primary middle, secondary middle to secondary middle) with inductors, of similar value (i.e., L ~ Zo * t_half).  Now you get asymptotically zero insertion loss at low frequencies, and at high frequencies, a 6dB shelf instead of the dips and peaks.

Aside of all of this, CMRR is asymptotically bad in the HF limit.  To address this, place a CMC on either side of the transformer, as much (equivalent) inductance as you can afford.  Add damping R+C across the transformer (P1 to S1, and P2 to S2) to control resonances, if necessary (these will be a large impedance, so will have little impact on HF response, despite their location).  The CMC inductance will resonate with the transformer isolation capacitance (and coupling/termination capacitance C, if used, as above), so this prevents that resonance from getting too peaky.  An isolation impedance in the low kOhms is very reasonable to achieve this way, and while that doesn't sound terrifically good, understand that we're talking with respect to radio frequencies here, where a thin wire in semi-free space is unlikely to reach half a kohm Zo.  This is doing as well as you can, given the limitations of real electromagnetism and not just some inductors and capacitors in a SPICE model. :)

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on August 05, 2018, 12:37:45 am

Now looking at injection transformer phase measurements:

The transformer phase plot shows the phase difference between the transformer primary and secondary. Some folks here say that the injection transformer is no longer useful when phase exceeds some value plucked from the chart. This needs a closer look.

If you look at the Signature Bode 100 gain vs Phase Margin chart, the point where gain is equal to 0dB the PM gives a very good indication of power supply stability. Doesn’t the injection transformer phase effect the PM of the power supply? The short answer is no. 

Thanks DT


What you write reminds me of a hefty discussion following a Texas Instrument Application note where they used a garden variety line transformer as an injection transformer and claimed its characteristics are irrelevant because it was "outside the loop".

It is OK to claim that (provided the secondary resistance is small enough) it does not alter the characteristics of the loop, but what it does alter is the amplitude and phase you measure at the loop output. You could calibrate this out using a VNA, but it is definitely a precision issue. When you look at the characteristics of the magnetic materials used for such transformers, the range of mu for a given frequency is 2 to 1. You can expect an coresponding low precision range for band corners. If your measurements are to be trusted, the phase shift induced by your transformer must be a) small and b) well known.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 05, 2018, 02:27:57 am
Here's a plot I made last year of the 10Hz - 10MHz magnitude response including some of the transformers mentioned in this thread, with 50 Ohm generator output, and xfmr terminated with 1 Ohm.

Curves from top down:
The dark blue is a toroid Tokin 10mH CM choke.
Magenta is the Jensen Iso-Max mentioned here several times. It is coax wound on a standard EI core, no doubt with carefully-chosen core material...
Green is the North Hills 0016 PA
Yellow is the North Hills 0017 CC
Red is a North Hills 1307 LB 75 Ohm unbal to 110 balanced transformer, used as a makeshift step-down xfmr, with one side of the 2ndary terminated in 50 Ohms and the output taken from the other side. Even this mild stepdown is sufficient to extend phase linearty vs Z to just beyond 100kHz, and so this is the xfmr I use with the circuit shown in post #102.
Cyan is a Ridley 15MHz Injection Transformer, a 10:1 step-down design, IIRC.

I would expect that the B-WIT 100 and the home-rolled version would behave pretty much the same, rolling off somewhere around 100kHz.

It would be interesting to make a 2:1 or 3:1 version to extend the 1 Ohm bandwidth. Hmmm...

EDIT : I learned yesterday that the Ridley is a 3:1 step-down winding ratio.
This makes it even more compelling to do a home-roll 2:1 or 3:1 version...
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 06, 2018, 09:42:11 pm
Hey guys and girls, I've just found out the secret sauce that North Hills adds to their wide bandwidth transformers

.

.

.

.

.

Yes, its "Bauschaum" (polyurethane foam)
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=491690;image)

This is a NH 12369 (obviously) video isolation transformer. Anyone's got a datasheet? I didn't find one. Will do some measurements later.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on August 06, 2018, 09:51:00 pm
Interesting that there's silver mica caps in there.

Pot cores are quite good, having more A_L than a toroid of the same size -- which means less wire length and more transformer bandwidth.  (Too bad amorphous isn't available in shapes!)

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 07, 2018, 02:23:30 am
transformer pr0n

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=491753;image)

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=491759;image)

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=491765;image)

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=491771;image)

The unit has 4 channels, three of them intended for video and one sync.
The sync channel has a small cap (labelled "100") across the input BNC.
The video channels have the silver mica ("471") connected from input (presumably BNC shell) to output (BNC shell).
The transformers are wound using twisted enamelled wire, the video channels have thicker wire than the sync channel.

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 07, 2018, 02:29:16 am
Some results:

The video channel has a magnetizing inductance of 112mH and the input to output coupling capacitance is 1.13nF (measured quite similar on all three channels).
For the sync channel, the results were 977mH and 1.9nF.

The frequency response (-3dB) for the video channels is 50Hz ... 78MHz, but the 45° phase shift response is from 50Hz to 14MHz - some tricks happening here - Note the bumps in the frequency response above 1MHz. This response looks the same for all three video channels. Termination was 50 Ohm for all measurements.

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=491777;image)

The sync channel shows a clean response from the low end of the HP3577A (5Hz) to 7.5MHz.

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=491789;image)

Estimating the wire length with the TDR shows a pretty clean impedance over length, somewhat varying around the expected 75 Ohm. Maybe 1.8m for the video transformers and around 6.8m for the sync. Assuming the real length in this ballpark, the high frequency response is way much better than the home rolled transformer using the nanocrystalline / amorphous core.

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=491783;image)
(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=491795;image)

Pretty good stuff this is!

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 07, 2018, 11:40:24 pm
The frequency response (-3dB) for the video channels is 50Hz ... 78MHz, but the 45° phase shift response is from 50Hz to 14MHz - some tricks happening here - Note the bumps in the frequency response above 1MHz. This response looks the same for all three video channels. Termination was 50 Ohm for all measurements.

I'm guessing you're using the 50 Ohms term in the 3577A. If you terminate the xfmr right at its output and set the analyzer to 1MegOhms, the mag/phase correlation at the high end should make more sense.

Quote
Pretty good stuff this is!

Agreed!
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 09, 2018, 02:06:52 am
I'm guessing you're using the 50 Ohms term in the 3577A. If you terminate the xfmr right at its output and set the analyzer to 1MegOhms, the mag/phase correlation at the high end should make more sense.

Yes, I'm using the internal termination. Shifting the termination towards the transformers output and setting the input to 1M doesn't make it any better, in contrary one can see even more bumps in the frequency response. I've used a rather short coax cable to connect the terminated transformer output to the 3577A. Maybe one would get better or at least other results using a compensated 10:1 oscilloscope probe.

In general, I'd prefer to see the transformers response when fed and terminated by its nominal impedance (75 Ohm for video stuff). I don't have the minimum loss pads to match to 3577A's 50 Ohm ports, so for now I'll stay with the 50 Ohm measurements.

And for the records, I'm making the measurement from Output to R input, in contrary to using a power divider and A/R as I prefer to see the system response over the transformers response fed from a virtual zero ohm source. Using the power divider and A/R measurement gives different results with notably extended low frequency response.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on August 09, 2018, 03:03:56 am

Now looking at injection transformer phase measurements:

The transformer phase plot shows the phase difference between the transformer primary and secondary. Some folks here say that the injection transformer is no longer useful when phase exceeds some value plucked from the chart. This needs a closer look.

If you look at the Signature Bode 100 gain vs Phase Margin chart, the point where gain is equal to 0dB the PM gives a very good indication of power supply stability. Doesn’t the injection transformer phase effect the PM of the power supply? The short answer is no. 

Thanks DT


What you write reminds me of a hefty discussion following a Texas Instrument Application note where they used a garden variety line transformer as an injection transformer and claimed its characteristics are irrelevant because it was "outside the loop".

It is OK to claim that (provided the secondary resistance is small enough) it does not alter the characteristics of the loop, but what it does alter is the amplitude and phase you measure at the loop output. You could calibrate this out using a VNA, but it is definitely a precision issue. When you look at the characteristics of the magnetic materials used for such transformers, the range of mu for a given frequency is 2 to 1. You can expect an coresponding low precision range for band corners. If your measurements are to be trusted, the phase shift induced by your transformer must be a) small and b) well known.


Hello,

I don’t know anything about a garden variety (straw man) line transformer.

I do agree there may be a falloff in amplitude. Both the Keysight and Bode 100 have built in provisions to adjust the test amplitude to within the small signal requirements of the error amplifier control loop. Even the best specialized injection transformers may sometimes need a little help.

I have seen no evidence that the change in phase in the injection transformer is evident in the phase measurement between the input of the error amplifier loop and the power supply output.

Any transformer, even the best specialized injection transformers may get a little wobbly if pushed into the anti-resonance/ resonance frequencies.

Thanks DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 09, 2018, 03:06:25 am
In general, I'd prefer to see the transformers response when fed and terminated by its nominal impedance (75 Ohm for video stuff). I don't have the minimum loss pads to match to 3577A's 50 Ohm ports, so for now I'll stay with the 50 Ohm measurements.

When it comes to xfmr-coupling, I'm a fan of "whatever works"   :)

Quote
And for the records, I'm making the measurement from Output to R input, in contrary to using a power divider and A/R as I prefer to see the system response over the transformers response fed from a virtual zero ohm source.

I'm not using a power divider, either. What is your "virtual zero ohm" source ?

Quote
Using the power divider and A/R measurement gives different results with notably extended low frequency response.

To me, characterizing a xfmr is set up like an FRA measurement; A/R, source Z same as it will be used, no power divider, high-Z inputs, and xfmr terminated in whatever the desired load is.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on August 09, 2018, 03:18:16 am
To me, characterizing a xfmr is set up like an FRA measurement; A/R, source Z same as it will be used, no power divider, high-Z inputs, and xfmr terminated in whatever the desired load is.

How do you calibrate/normalize this setup?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 09, 2018, 04:06:27 am
I'm not using a power divider, either. What is your "virtual zero ohm" source ?

That's was mistake in my conceptual thinking, whatever. I assumed, measuring the signal output at one side of the power divider would compensate for the total loading effect on the source. But it doesn't, it attenuates the loading effect to a lower impedance seen by the VNA - assuming using a resistive power divider. Anyway, measuring both the transformer input and output with high impedance R and A, then calculating A/R removes the loading effect of the transformer from the result. That's nearer to a virtual zero source impedance than the power divider method.

In practical appliation, e.g. for the said video stuff, one cannot take the loading effect out of the system, so I normalize R (transformer replaced by a "through") and then put the transformer in place to see the system response.

rx8pilot:
You'd normalize the  "FRA" setup by setting the VNA to sweep A/R phase and amplitude, the replace the transformer by a "through" and normalize. The 3577A then normalizes these traces (resulting in "A/R/D1" / "A/R/D2" as traces). This is at least how I'd normalize this setup. precaud pls confirm.

precaud:
At above some 10MHz the high impedance input mode of the 3577A doesn't work too well anymore, because of the 50 Ohm impedance of the internal and external cables involved. For lower frequencies, high Z should work fine and wouldn't require normalization anyway.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 09, 2018, 05:29:49 am
Couldn't leave that stuff alone ...

So I bodged a pair of minimum loss pads (50 Ohm <-> 75 Ohm) together and measured the video transformer again:
-3dB from 60Hz to 100MHz, +/-45° phase at 60Hz / 13Mhz, similar to my 50 Ohm measurement with the low frequency response shifted up (as one would expect from the increased source / sink impedance). Still some smallish bumps in the amplitude response above 1MHz.

Now, after some thinking, I replaced the "through" calibration piece (a male-to-male BNC adaptor) with a piece of 75Ohm coaxial cable of similar length to the guessed wire length within the transformer - somewhere in the 1.8m range.
After normalizing to this "through reference", the result is (guess what):
same as above for -3dB, but -45° phase at 45MHz.

So the internal wire length of the transformer causes some delay that leads to the misinterpretation -3dB implausible to phase.

BTW:
TDR'ing the transformer through the minimum loss pads shows a quite flat line - so these transformers clearly are made for 75 Ohm system impedance and have an impressive bandwidth then.

BTW 2:
The 3577A's "Length" setting achieves the same result as normalizing with the "through cable". Just set it to the negative value of your additionally introduced cable length to compensate for this.

BTW 3:
Pushing Leo Bodnar's fast pulses through the transformer gives a risetime of 4ns (vs. 400ps w/o the transformer, measuring the scope and matching pads). The transformer also adds some ringing to the square wave.

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 09, 2018, 10:55:43 am
That's was mistake in my conceptual thinking, whatever. I assumed, measuring the signal output at one side of the power divider would compensate for the total loading effect on the source. But it doesn't, it attenuates the loading effect to a lower impedance seen by the VNA - assuming using a resistive power divider. Anyway, measuring both the transformer input and output with high impedance R and A, then calculating A/R removes the loading effect of the transformer from the result. That's nearer to a virtual zero source impedance than the power divider method.

Well there can be good reasons for looking at it either way. I'm just concerned that future readers of this thread will look at all the measurements as if they're the same, when they're not.

Quote
rx8pilot:
You'd normalize the  "FRA" setup by setting the VNA to sweep A/R phase and amplitude, the replace the transformer by a "through" and normalize. The 3577A then normalizes these traces (resulting in "A/R/D1" / "A/R/D2" as traces). This is at least how I'd normalize this setup. precaud pls confirm.

Yes, and make sure whatever you'll be loading the xfmr with is in place for the sweep you use for normalizing.

Quote
precaud:
At above some 10MHz the high impedance input mode of the 3577A doesn't work too well anymore, because of the 50 Ohm impedance of the internal and external cables involved. For lower frequencies, high Z should work fine and wouldn't require normalization anyway.

Yes, for true high-Z measurements that wold be true. But not so much for a device with a 50 to 75 Ohm term. You can use normalize to test the impedance sensitivity of the measurement setup. Ex: normalize a "thru" sweep with 50 Ohm term, then change to a 75 Ohm term and it will plot the deviation. Anything that is not a flat line is a problem... phase deviation would be the most sensitive.

That's phenomenal bandwidth you're getting through that xfmr! What is it rated for?

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on August 09, 2018, 11:10:49 am
This thread has thrown me down a rabbit hole of thoughts, self-education, and experiments. Only learning more about magnetics and properly measuring them with a 25-year-old VNA can get me out of the hole.

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on August 09, 2018, 01:05:12 pm
This thread has thrown me down a rabbit hole of thoughts, self-education, and experiments. Only learning more about magnetics and properly measuring them with a 25-year-old VNA can get me out of the hole.

If it gets more people measuring, it can't be a bad thing. :)

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 09, 2018, 03:16:32 pm

That's phenomenal bandwidth you're getting through that xfmr! What is it rated for?

Don't know. Found it by chance on the evilbay (looking for North Hills after someone mentioned their transformers here), and decided to give it a try. No datasheet, no information, no similar part number found on the North Hills website. BTW, they've got some app notes about transformers and other interesting stuff.
So I just could guess: It's a RGB + sync video transformer, so I expected it to have wide BW to be useful, or it would be a common mode choke (North Hills calls them "Humbucker"). Former analog monitors having BNC RGB inputs achieved video bandwiths in excess of 100MHz.

http://www.nhsignal.com/products-wideband-video-isolation.html (http://www.nhsignal.com/products-wideband-video-isolation.html)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: ehughes on August 10, 2018, 07:01:11 am
For what its worth,    Omicron got at least 1 sale as a result of the tear down.    I just ordered one for QA checking out transducers.     Once it is up an running, I'll post some measurement results.     
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 12, 2018, 04:01:04 am
I see now where the 10 Ohms term comes from. Omicron uses is as the reference R for their low-Z measurements using the transformer:

https://www.omicron-lab.com/applications/detail/news/low-value-impedance-measurements/ (https://www.omicron-lab.com/applications/detail/news/low-value-impedance-measurements/)

I'm surprised they're not getting a higher useful bandwidth using the 10 Ohm reference (which also determines the minimum load on the transformer). I get 100kHz using similar topologies using a 1 Ohm reference.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on August 12, 2018, 04:12:29 am
Bandwidth is maximum at Zo, and drops off slowly for Z <> Zo.  The first-order approximation is thus: if LL and Lp are constant, then the LF cutoff is Z / (2*pi*Lp) and the HF cutoff is Z / (2*pi*LL).

For the frequencies and materials we're talking about here, this should be pretty close.  Note that the HF cutoff is actually a transmission line effect, not a dominant pole, so it will have slightly different response into other resistances (I forget if this is better or worse for BW).  For worse quality materials (like laminated iron), the permeability dependence on signal level and frequency is probably an important factor.

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 13, 2018, 01:25:57 am
This is a pretty interesting video, Ray Ridley comparing the three commercially-available isolation xfmrs at low frequencies.

http://www.youtube.com/watch?v=SKMCpywSyWk (http://www.youtube.com/watch?v=SKMCpywSyWk)

Unit "P" is clearly the Picotest.
Unit "O" is the Omicron.
I do wish he had also plotted transmission curves vs freq over the whole range of the transformers, measured into the same load R.
I had the Ridley 15MHz unit and it had a 10dB dip starting at around 10kHz, regardless of load.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: chris_leyson on August 13, 2018, 02:16:17 am
The Omicron Labs B-WIT 100 is only supposed to be driven at 0dBm not 13dBm. Interesting video from Omicron Labs where product "R" gets tested.

http://www.youtube.com/watch?v=b4FO9Pl9Np8 (http://www.youtube.com/watch?v=b4FO9Pl9Np8)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 13, 2018, 02:38:24 am
Yeah, the 15MHz Ridley unit I had looked similar in terms of flatness, though smoother at the high end than that one. The freq resp dip bugged me and so I sold it (perhaps hastily).
However, one could argue that, as long as the response does not change with level or load, and the variations are not extreme, for most FRA work, ultimate flatness is not critical...
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on August 13, 2018, 03:29:48 am
Unfortunately, neither Ridley nor Omicron tried to be especially objective with their presentations.

What would have been helpful are S21 curves that go over the whole frequency range, at given load impedances (e.g. 1/5/10/20/50 Ohms),
plus a curve for the allowable signal level for, say, 1% distortion over frequency, also for different load impedances. Also phase response is important
to know about.

It is very clear than one single device hardly fits all needs (High bandwidth, tolerant to strong signals with no distortion, low capacitances, not bulky ...)

There will versions with a deep low frequency limit - they are heavy and bulky, have a high coupling capacitance
There are smaller ones, which are small signal only, have medium frequency ranges, but lower capacitances, ...
...and the HF ones with very high bandwidth, very small signal tolerance, and small capacitance.

All marketing claims made in this industry has to be taken with a huge ROCK of salt. So have these videos.



Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Kleinstein on August 13, 2018, 05:36:16 am
If a really good injection transformer is that difficult, I would consider thinking about an active solution, with optical isolation, thus a kind of analog opto-coupler. In a simple form something like 2 photo-diodes in parallel to a load resistor. Without amplification it would be likely limited to low power (e.g. a few 10 mV) - but chances are it could work from DC to  beyond 10 MHz with low coupling capacitance.  If it needs an amplifier for the output this could be battery powered for good isolation.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on August 13, 2018, 05:44:54 am
Yes, this is a valid approach. If it is battery-powered and has a very fast (also low noise) optical isolator it competes very well with transformer solutions, especially at the low frequency range.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: ehughes on August 17, 2018, 04:12:08 am
We just got our Bode100.   It is a very nice piece of equipment and the software that come along is useful.    We are doing some analysis of a 1.8MHz piezo ring.  Specifically,  we are able to evaluate the epoxy in a transducer assembly.   

Yet nice piece of equipment and easily worth the money for our QA setup.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: voltsandjolts on August 19, 2018, 06:11:55 am
I was browsing the Picoscope site (I'm interested in their flexres 16bit/8bit scopes with arb gen that can do FRA) and found quite a nice video link about measuring loop gain with a DIY signal injection transformer. Looks like a nanocrystaline core from a common mode choke with about 7 metres of TP each for primary/sec - its at 9:00 minutes in, but the whole video is quite well done. Didn't achieve the bandwidth that others have here tho >:D

https://youtu.be/wKs8VyERZXU (https://youtu.be/wKs8VyERZXU)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 20, 2018, 02:32:32 pm
Here's a good reason NOT to use the Jensen IsoMax transformer for gain- and phase- margin measurements above 20kHz - above which the phase response changes with impedance... caused by the bandwidth increasing with increasing load R. The North Hills units are all better in this range.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on August 21, 2018, 07:34:55 am
Hello,

What you have shown is that the leakage inductance and load resistance form a low pass filter.

What you have not shown is that accuracy of the VNA Bode Plot is diminished.

The Bode Plot Phase Margin is independent of the transformer phase.(within limits) The VNA software has provisions to compensate for the attenuated transformer HF gain. (within limits)

DT

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 21, 2018, 09:01:26 am
What you have not shown is that accuracy of the VNA Bode Plot is diminished.

I haven't "shown" it, but I guarantee you it definitely is diminished, unless some post-processing is used to correct for it (Open/Short/Load). But even then, if the change is not fairly linear over the entire measurement range, the compensation math won't b able to correct for it accurately.

Quote
The Bode Plot Phase Margin is independent of the transformer phase.(within limits).

Not in my experience.

Quote
The VNA software has provisions to compensate for the attenuated transformer HF gain. (within limits)

Yes, some VNAs have "provisions" for it, but I have never seen any example of someone "normalizing" their VNA with the transformer in place prior to making a control loop measurement.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on August 21, 2018, 09:12:06 am
Curious why you started at 4R7.

What are you using to test it? How did you calibrate? I may do the same test to see if the results are similar (although I may use higher value loads) - but would want to match what you did.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 21, 2018, 09:36:54 am
Curious why you started at 4R7.

I didn't;  I started at 1R0, and ended at 4R7    :-DD

Most of what I use these for (output impedance measurements) loads the transformer between 1R0 and 5R0 on the high end. See the setup in this post:
http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/msg1720265/#msg1720265 (http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/msg1720265/#msg1720265)

For the measurement I posted, the setup is the same xfer function setup as others I've posted; both inputs at 1M, R measures xfmr input, T measures the output.

Quote
What are you using to test it?

AP Instruments 102B

Quote
How did you calibrate?

Huh? You want me to explain the 102B's cal procedure?

Quote
I may do the same test to see if the results are similar (although I may use higher value loads) - but would want to match what you did.

Please do. I get the same results regardless of the analyzer used.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: chris_leyson on August 21, 2018, 09:50:00 am
@voltsandjolts Nice video from Picoscope, thanks. Something has been bugging me about using 1:1 transformers and them terminating the secondary with 5 or 10 ohms. I would have gone for 2:1 or most probably 3:1 for a 5 ohm load. If I get time this week I will have a stab at a 3:1 transformer and see how it goes.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on August 21, 2018, 03:21:29 pm
Hello,

Open/Short/Load calibration is used for the impedance accessory test fixture and is not part of the VNA frequency gain / phase plot.

If you look in the Keysight E5061B User’s Manual you will the Open/Short/Load calibration procedure for Impedance Analysis option and optional impedance test fixture(s).

The available adjustment for the Frequency Gain / Phase Margin test is signal level. There is no adjustment needed for transformer phase.

The available test signal adjustment is for amplitude. The generator output level is adjusted to be within the small signal range of the DUT error amplifier. Over the LF range the signal level may need to be trimmed to reduce noise. Over other frequency bands the signal may need other tweaking. This tweaking is a iterate process looking for the cleanest Bode plot. This tweaking is more about the DUT than the injection transformer. (within limits)

DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on August 21, 2018, 09:05:31 pm
I agree completely.

The properties of your isolation transformers determine your dynamic range, even if the phase and amplitude response can be calibrated out by a good VNA.

What I do not understand in a lot of cases why manufacturers insist so much on a 1:1 ratio. I do not know a lot of examples except PFC where high signal injection amplitudes at low frequencies are really needed; In the absolute majority of cases you need rather small amplitudes in the millivolts range in order not to drive the DUT out of its linear range.

I did it with COTS ISDN transformers and a matching network., and it worked fine.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 21, 2018, 10:42:28 pm
Open/Short/Load calibration is used for the impedance accessory test fixture and is not part of the VNA frequency gain / phase plot.

My point exactly. So what exactly are you referring to when you said "The Bode Plot Phase Margin is independent of the transformer phase.(within limits)" ?

Quote
If you look in the Keysight E5061B User’s Manual you will the Open/Short/Load calibration procedure for Impedance Analysis option and optional impedance test fixture(s).

Yes, its unfortunate E5061B users need to buy an optional fixture to do it. We're not limiting our discussion to any particular analyzer. What one are you using?

Quote
The available adjustment for the Frequency Gain / Phase Margin test is signal level. There is no adjustment needed for transformer phase.

And that's where we disagree. If you make a measurement in a freq range where the xfmr magnitude and/or phase is not linear, it transfers directly into your measurement. How could it be otherwise? If would try it, you would see it is so.

Quote
The available test signal adjustment is for amplitude. The generator output level is adjusted to be within the small signal range of the DUT error amplifier. Over the LF range the signal level may need to be trimmed to reduce noise. Over other frequency bands the signal may need other tweaking. This tweaking is a iterate process looking for the cleanest Bode plot. This tweaking is more about the DUT than the injection transformer. (within limits)

Yes, that is for control loop testing. For impedance testing, the amplitude considerations are different. But it's not either/or; the same transformer can be used for both measurements, as long as you characterize it at the load it will be seeing, and use it within that range.

No matter what, the transfer response of the xfmr at the load it will see needs to be paid attention to.

Something has been bugging me about using 1:1 transformers and them terminating the secondary with 5 or 10 ohms. I would have gone for 2:1 or most probably 3:1 for a 5 ohm load. If I get time this week I will have a stab at a 3:1 transformer and see how it goes.

For impedance testing, I agree, and look forward to what you come up with. I'm gathering bits together to do a 2:1. For control loop, a 1:1 into 10 Ohms or above should be sufficient.

What I do not understand in a lot of cases why manufacturers insist so much on a 1:1 ratio.

Because they're easy to make. And they generally do the job.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 21, 2018, 11:22:13 pm
Open/Short/Load calibration is used for the impedance accessory test fixture and is not part of the VNA frequency gain / phase plot.

My point exactly. So what exactly are you referring to when you said "The Bode Plot Phase Margin is independent of the transformer phase.(within limits)" ?


So if you look up the AP Instruments Model 102B Manual (I found one here: http://www.apinstruments.com/files/102Bman.pdf (http://www.apinstruments.com/files/102Bman.pdf)),  Page 54 (PDF numbering) / 50 (document numbering) shows your typical FRA setup used. The VNA calculates the frequency response from the ratio of its inputs Channel A and Channel B. So the Source impedance and transformer phase / amplitude cancels out from the equation. No calibration required, just a good matching between Channel A and B (which one expects from a decent VNA).

Within limits of course, since one needs a minimum amplitude of source signal coupled through the transformer to get a useful signal above the noise floor.

And that's where we disagree. If you make a measurement in a freq range where the xfmr magnitude and/or phase is not linear, it transfers directly into your measurement. How could it be otherwise? If would try it, you would see it is so.
Same reason as above, the measurement of Channel A / B ratio cancels the transformer out of the equations.

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 21, 2018, 11:35:52 pm
So if you look up the AP Instruments Model 102B Manual (I found one here: http://www.apinstruments.com/files/102Bman.pdf (http://www.apinstruments.com/files/102Bman.pdf)),  Page 54 (PDF numbering) / 50 (document numbering) shows your typical FRA setup used. The VNA calculates the frequency response from the ratio of its inputs Channel A and Channel B. So the Source impedance and transformer phase / amplitude cancels out from the equation. No calibration required, just a good matching between Channel A and B (which one expects from a decent VNA).

Within limits of course, since one needs a minimum amplitude of source signal coupled through the transformer to get a useful signal above the noise floor.

OK, I see, for that topology the xfmr is literally doing nothing more than "injecting" the signal. So the xfmr requirements are relaxed, compared to what they are when using it for impedance measurement.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on August 22, 2018, 04:16:57 am

Quote
How did you calibrate?

Huh? You want me to explain the 102B's cal procedure?

I know the question sounds fundamental - and it is. This is a topic that I am new to and I have very little confidence in the results I am getting. I have been trying to better understand the network analyzer (in a general sense, not model specific), inductor measurements and analysis, and frequency response analysis of SMPS control loops. One of the things I am trying to figure out is essentially a 'sanity check' to make sure the results I am getting are reasonably accurate.

The part that I worry about is getting results that are close - but skewed enough that I end up chasing my tail. I don't have a solid intuition of how sensitive the measurements can be, where I can get false/skewed measurements and such. I think back to when I was learning to use an oscilloscope to measure delicate signals and the 10x passive probe had a huge ground clip connected directly to the power supply terminal. Everything looked broken, of course, and I spent a long time trying to add capacitors to reduce phantom noise. At some point - I learned how to use the instrument properly and of course, realized that there was never a problem - the measurements themselves were the problem.

Perhaps gathering the manuals for the AP VNA, Bode100, E5061-LF, etc would help me gain some confidence in how I am going about the process. Repeating some of the measurements in this thread should also help since I have the Jensen ISO-MAX VB-1BB that has been measured by a couple of people (comparison)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 22, 2018, 04:53:33 am
rx8pilot:
For building up some confidence in the cal and measurements procedures, I'd recommend to rebuild the HP35676A test set:
http://hparchive.com/Manuals/HP-35676-SCHEMATIC.pdf (http://hparchive.com/Manuals/HP-35676-SCHEMATIC.pdf)

No need for all the fancy metalwork, and don't worry about the unknown capacitor, it still works built on a piece of SMT protoboard using some MiniMelf resistors (some of the series connected to get near the original value).

Once calibrated using the full cal procedure (again, no need for a fancy cal standards set, a wire and a 50 Ohm resistor works, you'll get some ripple at the 200MHz end), then switching the 3577A to impedance display (choose "F4" as the input to display , it's written somewhere in the manual), you can get impedance sweeps of known components (start with resistors in the 10 Ohm to k Ohm range) and get familiar with the way it works. Measure some inductors and capacitors, read the imaginary part at some frequencies and do the math to verify your reading. Inductors are quite fancy regarding their impedance over frequency, many of them are inductors at rather low frequencies only.

There's also somewhere a manual on the net (for this or the HP35677 test set) that has a better description of how to measure impedance using the 3577A than the 3577A manual.

Edit: Found it, here it is: https://cb.wunderkis.de/wk-pub/Keysight%2035676A%20Data%20Sheet.pdf (https://cb.wunderkis.de/wk-pub/Keysight%2035676A%20Data%20Sheet.pdf)

Edit 2: Don't know what you mean by "skewed", the manual has some tips regarding the RBW setting: Reverse the sweep direction and watch if the graph shifts. If it does, your sweep speed is to fast for the chosen RBW.

Edit 3: "F4" is impedance for a 50 Ohm system and calibration, "F5" is for 75 Ohm

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on August 22, 2018, 05:11:14 am
Hello,

This is looking for the Sweet Spot.

Most of these injection transformers are set up for only a few ma of current before they saturate.
This transformer is wound on a VAC 250F core. This core has permeability that is much reduced from the VAC 500F core used in the B-WIT-100 transformer and will tolerate much more current before the onset of saturation.

The tradeoff is reduced band width, mostly trimmed off the LF end of the scale.

My impression is if you want to focus in on the LF use a different transformer. If you want to put the secondary of this transformer in series with the power supply to your audio amplifier to test PSRR this just might be the transformer to use.

This transformer is wound on a VACUUMSCHMELZE T60006-L2040-W964-02 250F core. There are 40 turns of CAT 6 plenum solid twisted pair.
 
@rx8pilot,

Thanks for sharing your approach to learning this stuff. You can look at all the various equipment user’s manuals, they don’t take much space to explain the interworking of stuff. The best single source I can recommend today is “Power Integrity”, Measuring, Optimizing, and Troubleshooting Power Related Parameters in Electronics Systems by Steven M. Sandler. https://www.amazon.com/Power-Integrity-Optimizing-Troubleshooting-Electronics/dp/0071830995/ref=sr_1_1?s=books&ie=UTF8&qid=1534877929&sr=1-1&keywords=power+integrity (https://www.amazon.com/Power-Integrity-Optimizing-Troubleshooting-Electronics/dp/0071830995/ref=sr_1_1?s=books&ie=UTF8&qid=1534877929&sr=1-1&keywords=power+integrity) . Cheep at$16.00

DT 
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 22, 2018, 05:24:27 am
From the frequency / phase response, I suppose you've used a rather low termination resistor for this transformer? This core has a quite low A_L (2.3uH @ 10kHz), so I'd expect a higher low frequency cutoff if it was terminated to 50 Ohm.
For comparability, you should specify its value.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on August 22, 2018, 05:31:24 am
Thank you.

For this plot the resistor is the 50Ohm resistor internal to the Bode 100.
Same as Dave used in the video.

DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on August 22, 2018, 05:45:32 am
Okay, thanks, still wondering. Doesn't match my experience with my home rolled transformers and the 3577A. I vaguely remember the Omicron having a "low impedance mode" for its output. What was the used source impedance? My 3577A has 50 Ohm output impedance, in case the Bode 100 was switched to something else, this might explain the difference.

Edit: did you measure "source" to "transformer output" ratio (including the source impedance into the measurement) or "transformer input" to "transformer output" (using two inputs of the VNA, excluding the source impedance)? I believe this is the reason for our different results, as I've done all the measurements the first way (using only one input).

BTW: didn't watch the whole video (sorry Dave), I do prefer reading stuff over watching videos
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on August 22, 2018, 06:30:49 am
Oops!

capt bullshot,

You were correct, I did not have the 50 Ohm output switched on. I switched on the 50 Ohm output and ran the plot again, this time down to 1 Hz.

The LF response was not noticeably changed. The HF response was slightly improved.

I will lug the 4395A VNA to the bench and run the plots on that VNA and post here.

Thanks DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on August 22, 2018, 07:20:13 am
@rx8pilot,

Thanks for sharing your approach to learning this stuff. You can look at all the various equipment user’s manuals, they don’t take much space to explain the interworking of stuff. The best single source I can recommend today is “Power Integrity”, Measuring, Optimizing, and Troubleshooting Power Related Parameters in Electronics Systems by Steven M. Sandler.

I actually met him at a trade show and purchased the book right there. It has been an excellent resource! There are, however, plenty of details that are hard for me to absorb without sitting at the bench and doing the work. Now that I have the gear, I have run out of excuses and just need to dive into the deep end. Sandlers book and all the other resources I have gathered are just now starting to make sense.

rx8pilot:
For building up some confidence in the cal and measurements procedures, I'd recommend to rebuild the HP35676A test set:
http://hparchive.com/Manuals/HP-35676-SCHEMATIC.pdf (http://hparchive.com/Manuals/HP-35676-SCHEMATIC.pdf)

No need for all the fancy metalwork, and don't worry about the unknown capacitor, it still works built on a piece of SMT protoboard using some MiniMelf resistors (some of the series connected to get near the original value).

Once calibrated using the full cal procedure (again, no need for a fancy cal standards set, a wire and a 50 Ohm resistor works, you'll get some ripple at the 200MHz end), then switching the 3577A to impedance display (choose "F4" as the input to display , it's written somewhere in the manual), you can get impedance sweeps of known components (start with resistors in the 10 Ohm to k Ohm range) and get familiar with the way it works. Measure some inductors and capacitors, read the imaginary part at some frequencies and do the math to verify your reading. Inductors are quite fancy regarding their impedance over frequency, many of them are inductors at rather low frequencies only.

There's also somewhere a manual on the net (for this or the HP35677 test set) that has a better description of how to measure impedance using the 3577A than the 3577A manual.

Edit: Found it, here it is: https://cb.wunderkis.de/wk-pub/Keysight%2035676A%20Data%20Sheet.pdf (https://cb.wunderkis.de/wk-pub/Keysight%2035676A%20Data%20Sheet.pdf)

Edit 2: Don't know what you mean by "skewed", the manual has some tips regarding the RBW setting: Reverse the sweep direction and watch if the graph shifts. If it does, your sweep speed is to fast for the chosen RBW.

Edit 3: "F4" is impedance for a 50 Ohm system and calibration, "F5" is for 75 Ohm



Thank you....excellent information!
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on August 22, 2018, 07:49:45 am
rx8pilot,

It is easy to make a mistake. I suggest that you check all the connections with a volt meter to confirm that the voltages are safe for your expensive test equipment. It is easy to vent the magic smoke.

Thanks DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on August 22, 2018, 08:18:07 am
rx8pilot,

It is easy to make a mistake. I suggest that you check all the connections with a volt meter to confirm that the voltages are safe for your expensive test equipment. It is easy to vent the magic smoke.

Thanks DT

The low-frequency operation makes AC coupling a challenge - I hope I can avoid blowing up my box. The HP 3577A has fairly decent overvoltage protection, but obviously, it has limits.

Measuring passive components is pretty safe, but doing FRA introduces a considerable risk of smoke. Not sure what the Bode 100 has in terms of input protection other than user selectable attenuators.

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 22, 2018, 12:24:44 pm
I know the question sounds fundamental - and it is. This is a topic that I am new to and I have very little confidence in the results I am getting. I have been trying to better understand the network analyzer (in a general sense, not model specific), inductor measurements and analysis, and frequency response analysis of SMPS control loops. One of the things I am trying to figure out is essentially a 'sanity check' to make sure the results I am getting are reasonably accurate.

Ah, I totally appreciate that. Previous advice given by others is very good. My uses tend more toward FRA than VNA, so I'll only add, I find it extremely useful to have a set of components (R's, C's, L's) that cover a wide range of values, which I have measured on other devices to compare my results to. "Confidence by Consensus".

Definitely put together a set of DC blocking cap fixtures for your 3577A. It's not a chance worth taking.

Quote
Perhaps gathering the manuals for the AP VNA, Bode100, E5061-LF, etc would help me gain some confidence in how I am going about the process. Repeating some of the measurements in this thread should also help since I have the Jensen ISO-MAX VB-1BB that has been measured by a couple of people (comparison)

I'd skip the stuff in AP's manuals about impedance measurement, it's pretty unsophisticated. They only cover the "Series-R" topology and do nothing to measure and remove residuals, which is necessary for good results.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on August 22, 2018, 01:29:48 pm
What kind of LF response do you target with your DC blocks?

Short and misplld from my mobile......

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 22, 2018, 01:58:35 pm
The 3577A low freq limit is 5Hz, so something below that. 100nF into 1MOhm gives -3dB a tad over 3 Hz. Scale to taste...
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on August 22, 2018, 02:16:20 pm
Oh, of course! I was fixated on 50 Ohm which is a totally different thing, lol.

For FRA, the receivers will (likely) always be 1M. That is when the system is in the danger zone..... connected to all kinds of power supplies where DC blocks are needed.

Does anyone know if the Bode 100 has AC coupled inputs? It did not look like it after scanning the brochure.

Short and misplld from my mobile......

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 22, 2018, 10:12:10 pm
Does anyone know if the Bode 100 has AC coupled inputs? It did not look like it after scanning the brochure.

I'm pretty sure it does. They demo the "shunt-thru" impedance technique, which requires 50 Ohm term on both channels, without adding an external term.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on August 23, 2018, 10:52:50 pm
Perhaps gathering the manuals for the AP VNA, Bode100, E5061-LF, etc would help me gain some confidence in how I am going about the process. Repeating some of the measurements in this thread should also help since I have the Jensen ISO-MAX VB-1BB that has been measured by a couple of people (comparison)

This app note from AP is more useful than their manual:

http://u.dianyuan.com/upload/space/2010/10/29/1288318638-361233.pdf (http://u.dianyuan.com/upload/space/2010/10/29/1288318638-361233.pdf)

The AP200 shown is the same as my 102B except it interfaces to the computer via a parallel port.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 04, 2018, 10:01:06 am
I wonder why Dave was so impressed by this transformer.

It's a heck of a lot better than some DIY ones I've used.

Hi Dave,

I was wondering what is so special with the Omicron B-WIT100 from your teardown transformer, and I was able to duplicate the transfer characteristics using two stacked cores from Vacuumschmelze (VAC), PN T60006-L2030-W514. The result are almost identical (all was measured on a Keysight E5061B-3L5 I now have on a test loan).

The big difference is the cost: My transformer is about 60 to 70€ including the box, the Omicron is about 500€ incl. VAT.

All the nittigritti is documented here (at the bottom):

https://electronicprojectsforfun.wordpress.com/injection-transformers/


Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on October 04, 2018, 10:10:20 am
I was wondering what is so special with the Omicron B-WIT100 from your teardown transformer, and I was able to duplicate the transfer characteristics using two stacked cores from Vacuumschmelze (VA), PN T60006-L2030-W514. The result are almost identical (all was measured on a Keysight E5061B-3L5 in now have on a test loan).

The big difference is the cost: My transformer is about 60 to 70€ including the box, the Omicron is about 500€ incl. VAT.

All the nittigritti is documented here (at the bottom):

https://electronicprojectsforfun.wordpress.com/injection-transformers/

I am VERY thankful for this write up @Wolfgang!  :-+.
It so happens that I have the exact same core sitting on my bench and it is about to become my new injection transformer.
Not sure why this is so interesting and fun.....but it is.

Off to do some winding now.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 04, 2018, 10:31:41 am
Do you want the STL for the holder ?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on October 04, 2018, 10:56:16 am
All the nittigritti is documented here (at the bottom):

https://electronicprojectsforfun.wordpress.com/injection-transformers/

One heckuva job, Wolfgang!    :-+
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on October 04, 2018, 11:21:25 am
Do you want the STL for the holder ?

For sure, I don't have a 3D printer but I can CNC machine it from Delrin.

I will probably machine a case for it and give it a fun name: NVT-1

Nude Virgin Transformer - 1
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 04, 2018, 11:44:57 am
... for all interested: I uploaded the STL file of the holder in a ZIP and the webpage has the link in it now.

Have fun !
  Wolfgang
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on October 04, 2018, 11:57:55 am
Thank you so much, this is a great project.

Short and misplld from my mobile......

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 04, 2018, 12:01:10 pm
Do you want the STL for the holder ?

For sure, I don't have a 3D printer but I can CNC machine it from Delrin.

I will probably machine a case for it and give it a fun name: NVT-1

Nude Virgin Transformer - 1

NVT1 - A Good name, why not. I'll make a label for it tomorrow.

Delrin is the same as POM? I like it too but the electrostatic chips when milling drive me nuts. There is no place where they dont stick to.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on October 04, 2018, 01:10:21 pm
And for the graphics.....
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on October 05, 2018, 03:06:38 am
Wolfgang,

Such pride?

Been there done that.

The VAC T60006-L2030-W514-03- core appears to be an exact match for size and color for the core in the real B-Wit injection transformer.

See Reply #79 for a photo.

See Reply #96 for a plot (identical to the real deal)

It all fits into a cute little Hammond box just like the real deal.

DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on October 05, 2018, 04:33:19 am
Wolfgang,

Such pride?

Been there done that.

Now, now.....
The write up by Wolfgang is really nice....and seeing some of the initial efforts is very interesting.

The VAC T60006-L2030-W514-03- core appears to be an exact match for size and color for the core in the real B-Wit injection transformer.

See Reply #79 for a photo.


This is exactly why I already have one on my bench....I put it in my next Mouser order. Good work, thank you.

See Reply #96 for a plot (identical to the real deal)


Do you have this plot scaled by chance? The db/div and deg/div are rather course in the range of interest. Not too critical, but the conversation has been splitting hairs and the precision of your plots are bigger than a hair  :-DD.



Back to one of the earlier questions.....
Why does the response need to be so flat and phase perfect when the calibration of the VNA can null out the transformer response?
Are nude virgins actually helping here?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 05, 2018, 04:39:26 am
Wolfgang,

Such pride?

Been there done that.

The VAC T60006-L2030-W514-03- core appears to be an exact match for size and color for the core in the real B-Wit injection transformer.

See Reply #79 for a photo.

See Reply #96 for a plot (identical to the real deal)

It all fits into a cute little Hammond box just like the real deal.

DT

Hi,

I disagree that it is the same core.

The datasheet of your part is here:

https://www.vacuumschmelze.de/fileadmin/Medienbiliothek_2010/Produkte/Kerne_und_Bauelemente/Anwendungen/Kerne/Kerne_SKDs_Kunststoff/W514.pdf (https://www.vacuumschmelze.de/fileadmin/Medienbiliothek_2010/Produkte/Kerne_und_Bauelemente/Anwendungen/Kerne/Kerne_SKDs_Kunststoff/W514.pdf)

the core in my B-WIT100 (I disassembled it today to check) has a diameter of 42mm.

Maybe they changed the core during production, I dont know.

The internals of the box I did not like so much. Its all antistatic mats and glue, the fuse is soldered and insulated by shrink-wrap, only one side is fused, ...
Not a convincing expression of quality, for 500€, I would say. So the real deal is not exactly a good deal.

To make my own was a challenge and a prank. I do know its not rocket science, and it was just a fun thing. See last photo on my "injection Transformers" page.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 05, 2018, 05:02:26 am
Hi,

the reason why you should not rely on nude virgins but rather have a good injection transformer is measurement accuracy. It is correct (it was the prime argument of the Texas instruments people in their Bode papers) that the transformer can be normalized out, but:

- the problems occur at the band corners, where the S21 of the transformer deviates from 1 a lot (e.g., 10dB for the B-WIT100 at 1Hz).
  Lets say we are at the low frequency range (there its most prominent) for now.
- your injection amplitude is now 10dB down, say, i.e. your measurement noise goes up
- If you try to increase drive level, you will soon run into core saturation problems creating harmonics and all other kinds of dirt effects.
  The lower the frequency gets, the more pronounced this problem is. Dont forget that allowable DC-AC current to avoid saturation is in the range of 10mA.

- At the high frequency edge stray inductances and interwinding capacitances could make your measurements problematic, because the parasitic elements are
  normally not very well known.

So, transformer imperfections can be calibrated out, but at the cost of less dynamic range.

I think what we got here is about the max that can be expected from a single-transformer design.
When you look at the market, they have special transformers for the low end (Ridley, Picotest, Omicron, ...) with heavy cores. Their high-end behaviour is bad, however. The small cores do it just the other way. It only depends what you need.

Techniques that could work (I never tried, just saw some literature) are stacked transformers, each for its own frequency band, ...)
To make this is extremely tricky, involves extended alignment and compensation and you can be glad to get a factor of 10 in frequency range over normal cores.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: ogden on October 05, 2018, 05:13:21 am
- the problems occur at the band corners, where the S21 of the transformer deviates from 1 a lot (e.g., 10dB for the B-WIT100 at 1Hz).

Are you really not sure about your DC supply stability below 1Hz? Or even 100Hz?  :-//
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 05, 2018, 05:21:16 am
Hi,

what I hear the problems at low frequencies are a peculiarity of the PFC (power factor correction) people. Dr. Ridley has a video about this; they attack a PFC regulator by imposing strong sub-Hz disturbances and then check if the PFC IC still works. For normal linear PSUs, LF instability is not likely to occur because most PSU at least are good enough to suppress rectified line ripple, around 100Hz in Europe. Switching regulators with several regulating loops working parallel are a different matter. There testing LF also makes sense.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on October 05, 2018, 05:56:27 am
Apologies,

Back on June 7th I opened the B-WIT-100 and measured the core inside and went to Mouser to see if I could find the part. I just looked up the part that I ordered and used to make the Home Roll transformer is this one: https://www.mouser.com/datasheet/2/599/W424-237924.pdf (https://www.mouser.com/datasheet/2/599/W424-237924.pdf) . In error I posted the wrong part number in Reply #79.
 
The photo and plot are the correct items.

In terms of plots with a finer scale what I posted is what you get from the Bode 100 software. The Bode 100 and software does record precise data points that will split fine red hair.

All the conversation about gain and phase at the tails of the plots I believe is mostly arm waving. The Bode 100 or for that matter any VNA will do Thru calibration and correct for a moderate degree of Phase and Gain variation.

Again I am sorry for posting by mistake the incorrect part number, this is the part in the photo and tested and appears to be very close to the B-WIT-100 core.

https://www.mouser.com/datasheet/2/599/W424-237924.pdf (https://www.mouser.com/datasheet/2/599/W424-237924.pdf)


Thanks DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 05, 2018, 06:22:14 am
Dont worry, many ways lead to Rome.

One should not forget that the cores have tolerances of a few 10 percent up and down. The difference between the homebrew curves and the B-WIT100 are probably less than the average variation between different B-WIT100 units.
The core you used has an average Al of 109, the one I used has one of 94. The mouser part number you gave has no plastic trough filling around it as mine and the one used in the B-WIT100. I know that only german readers can identify this difference. So maybe you got yourself a similar, but not the same part.

I am not completely in agreement with the idea that the Bode 100 will kill *all* problems. For PFC, there are probably better (sub 1Hz) machines, and for ultra-high frequency switchers you probably need another lineup of injectors. I have no big trust in banana wired setups at 50MHz. Another field where I have not worked myself in sufficiently yet is the measurement of really small impedances like PDNs on digital boards.

At the moment I am testing the E5061B-3L5 and the Bode 100 in parallel and the agreement at low frequencies is good (10MHz). Above that I would believe the E5061B-3L5 a lot more (upper limit is 3GHz). But - no final results here yet.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on October 05, 2018, 06:28:35 am
@Wolfgang HA! :-DD

Funny.....
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: ogden on October 05, 2018, 07:18:03 am
what I hear the problems at low frequencies are a peculiarity of the PFC (power factor correction) people. Dr. Ridley has a video about this; they attack a PFC regulator by imposing strong sub-Hz disturbances and then check if the PFC IC still works.

Oh, PFC people. They are supposedly rich, right? ;) - I would say that sub-1Hz job is not easy for transformer. To cover low frequency range down to DC one could try isolation amplifier (http://www.analog.com/en/products/adum4190.html#product-overview) based "injection transformer"
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 05, 2018, 07:29:53 am
... the video shows a transformer that has a few 100g (Dr. Ridley *weighs* them as a criteria for quality) and then he weighs all the others (and concludes that they are too light for the hard job). Irony apart, of course you could always throw some kilograms of iron and copper at any LF problem it will work. It wont be cheap, however, and an independently powered solid-state injector could be a better option. There are quite some on the market.

Whatever you see at Ridley, Omicron, Picotest or Keysight is made to make their own products shine. Independent thinking is key to not fall into a vendors honeypot. The matter is tricky, there are many pitfalls, and a lot of info is not very well communicated. Lots of work to do !
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on October 05, 2018, 07:44:17 am
When Ridley got out the scale, I almost fell out of my chair.

All I really care about is how it performs in real life - it was really unexpected from a person with his pedigree and credentials. That type of sales pitch really degrades his own line of products for me.

And yes, for the really low frequencies - a solid state solution is a clear winner in performance at that expense of complexity.

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 05, 2018, 07:50:47 am
The Omicron people have their own videos where their products shine and Ridleys dont (no surprise, the focus on bandwidth and flatness, where the big super-LF stuff flunks out in the 10kHz range). There is no such thing like a single size that fits all. Check what you really need, try all yourself and let the salesmen talk as much as they may.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Bud on October 05, 2018, 08:53:15 am
Why does the response need to be so flat and phase perfect when the calibration of the VNA can null out the transformer response?

In general you want errors to be as small as possible to reduce dependency on stability of calibration, because of time or temperature changes,etc.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Bud on October 05, 2018, 08:57:48 am
@Wolfgang HA! :-DD

Funny.....

You can bet someone is about to get offended and , given the placement of the transformer symbol, ask what do you mean by "injection"  :-X
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on October 05, 2018, 09:12:50 am
One size does not fit all.

The high permeability cores saturate easily with only a handful of ma’s current. This one I used a much lower permeability core and tested inductance with up to 100ma with no sign of saturation. The lower permeability also results in less LF performance. (tested with Rhode HN8118 LCR meter)

This injection transformer is intended to be in series with the power supply and test audio amplifier PSRR.

I have misplaced the APx555 output plot.

DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 05, 2018, 09:38:44 am
@Wolfgang HA! :-DD

Funny.....

You can bet someone is about to get offended and , given the placement of the transformer symbol, ask what do you mean by "injection"  :-X

IMHO, its a harmless prank, and the words came from the master of all this forum himself, Dave.
The picture is a classic Amadeo Modigliani, and no obvious sexuality is shown.
This is art, not porn.  :-+ Smut is in the eye of the beholder (Tom Lehrer).
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 05, 2018, 09:44:00 am
The plot would say more with a proper scale (1dB/div) for gain.

The problem with high-mu cores saturating with small DC currents is well known.

Two ways out exist:
- lower mu, with worse LF response as a consequence
- dont change core, but let no DC go thru it by using a huge blocking cap.

There is some Keysight literature about how to do this.

What is the frequency range you would like to cover ?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on October 05, 2018, 10:33:38 am
No Problem.

This transformer demonstrates that one size does not fit all.
 
It is installed at the output of a DC power supply.

The frequency range is from below 10hz to mid Mhz range.

This transformer will test Amplifier and Power Supply Rejection Ratio.

DT
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 05, 2018, 10:39:07 am
Hi,

just a hint: you could do it in two sweeps, with the LF part covered by a fat transformer (Omicron, Ridley, Homebrew by stacked cores, ...)
and a normal transformer for the higher frequency part.

Just a question: Why are you testing up to a few MHz ? Are you afraid of amp instabilities of RFI problems ?

Do you want to try a core that withstands a lot of DC current or by the Keysight method with a DC block cap so the transformer always runs in AC mode ?

How many amps does your supply current have ?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on October 05, 2018, 12:38:01 pm
Hello,

I want to keep this as simple as possible and only add complexity as needed. Audio Precision uses a Jensen JT-123-BLCF transformer for this application in their technote 106 (you need to sign in at the AP.com site to download the technote). https://www.ap.com/download/technote-106-measuring-psrr-power-supply-rejection-ratio-2/?wpdmdl=5795 (https://www.ap.com/download/technote-106-measuring-psrr-power-supply-rejection-ratio-2/?wpdmdl=5795)

I am looking for a transformer that will withstand maybe 200ma or 300ma, so far 50ma is enough. I have used this transformer with a 12B4A audio tube amp tube circuit biased to ~ 35ma. The 12B4A will oscillate if you give it a chance.

Why test to a few Mhz? Afraid? No. Yes I am looking for wider bandwidth than the Jensen transformer. I do want to take a look for RF and possibly other oddities even oscillation. Mostly it is fun to look.

I am not opposed to the Keysight method. Perhaps you can supply a reference. I do have Keysight instruments on the bench and Keysight books on the shelf.

Thanks DT

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 05, 2018, 08:33:03 pm
Hello,

I want to keep this as simple as possible and only add complexity as needed. Audio Precision uses a Jensen JT-123-BLCF transformer for this application in their technote 106 (you need to sign in at the AP.com site to download the technote). https://www.ap.com/download/technote-106-measuring-psrr-power-supply-rejection-ratio-2/?wpdmdl=5795 (https://www.ap.com/download/technote-106-measuring-psrr-power-supply-rejection-ratio-2/?wpdmdl=5795)

I am looking for a transformer that will withstand maybe 200ma or 300ma, so far 50ma is enough. I have used this transformer with a 12B4A audio tube amp tube circuit biased to ~ 35ma. The 12B4A will oscillate if you give it a chance.

Why test to a few Mhz? Afraid? No. Yes I am looking for wider bandwidth than the Jensen transformer. I do want to take a look for RF and possibly other oddities even oscillation. Mostly it is fun to look.

I am not opposed to the Keysight method. Perhaps you can supply a reference. I do have Keysight instruments on the bench and Keysight books on the shelf.

Thanks DT



Some comments to that:

- Your Jensen transformer covers the audio range only, and one winding (of 4) has 20 Ohms already. I have missed a DC current tolerance spec in the datasheet.
- it could well be that even a moderate DC current of a few 10 mA drives it into saturation so much that the inductance goes down a lot.
- What you might need is an output transformer for tube class A linears. They are used to DC bias.
- Info about some Keyside tricks can be found here:
http://literature.cdn.keysight.com/litweb/pdf/5990-5902EN.pdf (http://literature.cdn.keysight.com/litweb/pdf/5990-5902EN.pdf)

hope that helps because 10Hz to a few MHz with up to 300mA DC - thats a challenge.

  Wolfgang

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: MilkmanCDN on October 19, 2018, 10:53:18 am
@DualTriode,

Thanks for updating the correct BWIT transformer part number.   In my haste I ordered 3x of the wrong one and was wondering why I could only get 30 turns around the transformer, instead of 40.    Looks like the correct transformer is a little larger.   It's all making sense now.   New order placed.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Relaxe on October 24, 2018, 07:40:25 am
Thanks for your work Wolfgang!

Can you tell us the part # of the Hammond Box?
I want to duplicate this here...
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 24, 2018, 09:58:22 am
Hi,

I am not a home at the moment, but I think it was a 27134PDLA Hammond / Eddystone series box.
If you wait until monday I can look it up to be 100% sure.

Regards
  Wolfgang
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Relaxe on October 25, 2018, 12:58:06 am
Thanks,

As the 27134PDLA is not available at Digikey/Mouser, I will fit it in the dimensionaly similar 1590T.

About the Fuse: I have selected LittleFuse 0251001.NRT1L . Does the series resistance  (0.128 Ohms) affects the circuit?

About the injection resistor, I have seen documentation claiming the resistor must match the transformer impedance. Picotest’s J2101A recommend a 5 Ohm resistor. What do you recommend?

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: T3sl4co1l on October 25, 2018, 01:10:38 am
As seen in the rest of this thread -- lower load resistance extends LF response, at greater expense to the HF response.  HF response is most when source and load are matched; but you may not need this range, so that may be an acceptable tradeoff.

The load resistance is usually made low so that it does not interfere with the circuit it's introduced to.

Tim
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 25, 2018, 06:27:34 am
Thanks,

As the 27134PDLA is not available at Digikey/Mouser, I will fit it in the dimensionaly similar 1590T.

About the Fuse: I have selected LittleFuse 0251001.NRT1L . Does the series resistance  (0.128 Ohms) affects the circuit?

About the injection resistor, I have seen documentation claiming the resistor must match the transformer impedance. Picotest’s J2101A recommend a 5 Ohm resistor. What do you recommend?

Hi,

I bought mine at Conrad electronics (I found an old email). I dont know if you have something similar in Canada. The box does not really matter. Now for the fuse: The allowable DC current for the high-mu cores is very small, in the range of 10mA. The fuse is just there to prevent destructions by dead  shorts. The wire resistance of the windings is a few 100Ohms so I see no issue with the fuse resistance. In total we are way below 1Ohm.

best regards
  Wolfgang
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Relaxe on October 27, 2018, 07:13:39 am
I just did mine,
Here's the BOM, using Mouser parts:

2x 983-T60006-L2030W514
2x 576-0251001.NRT1L
1x 546-1590T
1x 530-108-0903-1
1x 530-108-0902-1
1x 571-5-1634523-1
1x 71-AVE030020E16R0KE
optionnal: 1x 372-U1163A
I used less than 3m of twisted pair wire from a CAT7 patch chord I had laying around.

Total cost: 95 Canadian $.

Did not test yet, but posting to share the love.
Thanks again Wolfgang!
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 27, 2018, 07:41:47 am
Cool ! The little green things are fuses, am I right ?
Curious for the measurements now, of course !!

Regards
  Wolfgang
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: _Wim_ on October 27, 2018, 11:17:50 pm
I also made a couple of these in a while ago posted about them here (including measurements):

http://www.eevblog.com/forum/testgear/looking-for-a-low-cost-way-of-measuring-dc-dc-converter-control-loop-response/msg1738013/#msg1738013 (http://www.eevblog.com/forum/testgear/looking-for-a-low-cost-way-of-measuring-dc-dc-converter-control-loop-response/msg1738013/#msg1738013)

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on October 28, 2018, 01:09:54 am
Thanks, I've already seen tham. Good site !
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: MilkmanCDN on November 07, 2018, 12:31:35 pm
Curious, what's the rating on the fuses that you used?    I'd assume it's fairly large  (>1A) as we're only trying to prevent wires from over-heating during transformer saturation.   
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Relaxe on November 29, 2018, 12:16:32 pm
Hey guys

I finally got around using the thing.
I installed the demo of Frequency Response Analysis option for the DSOX3000T scope. It uses the onboard signal generator and scope probes to do the magic.
To qualify my NVT-1, I plugged a BNC from the WaveGen to the VNT-1 Input, and both scope probes to the VNT-1 output.

Looks like a pretty flat response!

I attached the image of the plot, setup, and the .CSV of the results.

@MilkmanCDN: I Used 1 Amp fuses. See Mouser part#.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on November 29, 2018, 12:59:03 pm
Curious, what's the rating on the fuses that you used?    I'd assume it's fairly large  (>1A) as we're only trying to prevent wires from over-heating during transformer saturation.   

Yes, I used a few 100mA IIRC. The purpose is to prevent buring the wires. The core will saturate way before that will happen.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on November 29, 2018, 01:00:49 pm
Hey guys

I finally got around using the thing.
I installed the demo of Frequency Response Analysis option for the DSOX3000T scope. It uses the onboard signal generator and scope probes to do the magic.
To qualify my NVT-1, I plugged a BNC from the WaveGen to the VNT-1 Input, and both scope probes to the VNT-1 output.

Looks like a pretty flat response!

I attached the image of the plot, setup, and the .CSV of the results.

@MilkmanCDN: I Used 1 Amp fuses. See Mouser part#.

Looks fairly flat and OK to me ! And now much fun with the virgins !  :)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: DualTriode on November 29, 2018, 05:28:12 pm
Nice scope.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: rx8pilot on December 02, 2018, 12:52:16 pm
I finally got mine wound up and made a signal splitter for my HP 3577A. Still, I need to add some AC coupling on the inputs.
I think I am now set up for a new SMPS design I am building.

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: sixtimesseven on December 10, 2018, 01:11:15 am
rx8pilot:
For building up some confidence in the cal and measurements procedures, I'd recommend to rebuild the HP35676A test set:
http://hparchive.com/Manuals/HP-35676-SCHEMATIC.pdf (http://hparchive.com/Manuals/HP-35676-SCHEMATIC.pdf)

No need for all the fancy metalwork, and don't worry about the unknown capacitor, it still works built on a piece of SMT protoboard using some MiniMelf resistors (some of the series connected to get near the original value).

Once calibrated using the full cal procedure (again, no need for a fancy cal standards set, a wire and a 50 Ohm resistor works, you'll get some ripple at the 200MHz end), then switching the 3577A to impedance display (choose "F4" as the input to display , it's written somewhere in the manual), you can get impedance sweeps of known components (start with resistors in the 10 Ohm to k Ohm range) and get familiar with the way it works. Measure some inductors and capacitors, read the imaginary part at some frequencies and do the math to verify your reading. Inductors are quite fancy regarding their impedance over frequency, many of them are inductors at rather low frequencies only.

There's also somewhere a manual on the net (for this or the HP35677 test set) that has a better description of how to measure impedance using the 3577A than the 3577A manual.

Edit: Found it, here it is: https://cb.wunderkis.de/wk-pub/Keysight%2035676A%20Data%20Sheet.pdf (https://cb.wunderkis.de/wk-pub/Keysight%2035676A%20Data%20Sheet.pdf)

Edit 2: Don't know what you mean by "skewed", the manual has some tips regarding the RBW setting: Reverse the sweep direction and watch if the graph shifts. If it does, your sweep speed is to fast for the chosen RBW.

Edit 3: "F4" is impedance for a 50 Ohm system and calibration, "F5" is for 75 Ohm

Hi

I had planed to rebuilt the HP 35676 but I have some questions regarding it's operation as described in the manual.
First of all, if I look at this schematic, it seems to me that the 80R6 is the current sensing shunt resistor. The rest is pretty much a ~13dB T-attenuator for the reference input and a ~9dBm T-Attenuator on the voltage sensing A input.  At least that is what I first thought.

But when I read the manual, I see that for one port measurment the A/R and for 2-port the B/R functions are applied. So this would mean measurements of "V" "only"(?) In this case I assume the 80R6 resistor is used to match the two T-Attenuators which don't seem to have a 50ohms input impeadance on their own.

But, what if one would like to do V/I measurments? Could I use the 80R6 resistor as a shunt like I first thought and measure voltage over the DUT on the A port, and current trough the DUT via R-B measurment and terminate the DUT either in 50ohms / B input for a 50Ohm system or lets say at ground for a capacitor / inductor with =/ 50ohms?
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: capt bullshot on December 10, 2018, 05:11:57 am

I had planed to rebuilt the HP 35676 but I have some questions regarding it's operation as described in the manual.
First of all, if I look at this schematic, it seems to me that the 80R6 is the current sensing shunt resistor. The rest is pretty much a ~13dB T-attenuator for the reference input and a ~9dBm T-Attenuator on the voltage sensing A input.  At least that is what I first thought.

But when I read the manual, I see that for one port measurment the A/R and for 2-port the B/R functions are applied. So this would mean measurements of "V" "only"(?) In this case I assume the 80R6 resistor is used to match the two T-Attenuators which don't seem to have a 50ohms input impeadance on their own.

But, what if one would like to do V/I measurments? Could I use the 80R6 resistor as a shunt like I first thought and measure voltage over the DUT on the A port, and current trough the DUT via R-B measurment and terminate the DUT either in 50ohms / B input for a 50Ohm system or lets say at ground for a capacitor / inductor with =/ 50ohms?

Don't know if I can answer your question to your satisfaction. Afaik, the 35676 is just a voltage divider (the said 80R6 vs. the input impedance of the DUT). So the 3577 can measure the ratio of A to R and calculate the DUT's impedance within a limited range. There's no way to directly measure the current through the DUT. 
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: MilkmanCDN on January 26, 2019, 03:42:04 am
Folks,

I finally finished putting my isolation transformer together.   Took a little longer than I would have liked, and Dave is bang on regarding $500 being an acceptable price.    Researching/purchasing all the right bits/pieces, winding the transformer, and testing took me quite a few hours.

My bill of materials is:

I reduced the cost of the transformer by building multiple (x3) as a couple of friends wanted one.    I estimate that the cost of materials to construct is around ~$65 - $80 USD per transformer.   I've got around 10-20 hours into this project.

I've attached a copy of the Visio diagram that I used to create both the drill templates and stickers.   

Pictures of the unpainted metal boxes, drilled boxes, internal components, and finished transformers are attached.   I decided to call the transformer ANVT-100 as a play on Dave's review.   I did test these transformers using a scope/function-generator and performance is right in line with what has been previously posted here.    When I get a chance, I'll circle back and post a proper bode plot from the Venable at the office.

A big thanks to all on this forum.    Especially Wolfgang and DualTriode for sharing their build and test details.   Lot's of great information here and really helpful folks.   

Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on January 28, 2019, 11:17:00 am
Chapeau ! Looks VERY close to the original. I find my nude virgin label more attractive, however.  :)
Why you have just *one* fuse ?

Wolfgang
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: MilkmanCDN on January 29, 2019, 05:26:28 am
Thanks Wolfgang,

I only put one fuse because it's typically the driving side (BNC input) that injects current.   However, given that the transformer could be used in both directions, and the secondary can also be subject to higher currents, I suppose putting one on both sides would be prudent.   That said, the original BWIT-100 only has a fuse one-side as well.

I also think your label is much more attractive; however, it's resemblance to a famous internet meme (think goats), might get the box banned from my household.   I'm pretty sure my wife wouldn't approve.    :)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on January 29, 2019, 06:02:31 am
... in the end, its a classic piece of art by Modigliani recently sold for more than 100 million at Sotheby's.
Its undisputably *art*, nothing else. Be strong and defend the liberty of free expression !!  >:D

You know what: an engineer from Omicron had a burst of laugh when he saw it - these people are OK, and their sense of humour is OK too.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: precaud on January 29, 2019, 07:22:08 am
You know what: an engineer from Omicron had a burst of laugh when he saw it - these people are OK, and there sense of humour is OK too.

That is my impression of them, too.
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: MilkmanCDN on February 09, 2019, 09:17:12 am
... in the end, its a classic piece of art by Modigliani recently sold for more than 100 million at Sotheby's.

I see what you did there.   
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on February 09, 2019, 09:40:02 am
Honi soit qui mal y pense.  :) 8)
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Jay_Diddy_B on February 13, 2019, 11:10:11 am
Hi group,

I see a lot of people have winding their own NVTs.  I want to share an alternative approach.
You simply buy the B82720H0015A035 EPCOS (TDK) from Digikey. They cost $2.66 USD or $3.66 CDN.

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=650586;image)

This part is quite small:

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=650592;image)

Here is the spec:

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=650598;image)

The magnetizing inductance is 68mH, not as high as the NVTs, but still quite high. The leakage (stray) inductance is 1200nH.

In a 50 \$\Omega\$ test circuit:

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=650604;image)

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=650622;image)

The modelling results show a 3dB bandwidth from 60Hz to 13 MHz.
The model does not include any capacitance.

Measured results:

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=650610;image)


The low frequency 3dB point is 50 Hz

(http://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/?action=dlattach;attach=650616;image)


The high frequency 3dB point is 4MHz.

The transformer does not have to be flat in the normal control loop measuring scheme.

This common mode choke, used as a transformer, is suitable for most power supply control loop analysis.

Regards,

Jay_Diddy_B
Title: Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
Post by: Wolfgang on February 13, 2019, 12:07:08 pm
Hi,

why not ? If you can live with the bandwidth restrictions, its a cheap alternative. The cores I used cost some 10€ each.

Thanks !
  Wolfgang