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Author Topic: DIY Ghz sampling head for <100Mhz scopes  (Read 11906 times)

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Offline Alex Eisenhut

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #25 on: May 14, 2016, 10:33:46 AM »
Don't forget this monster

http://w140.com/tekwiki/wiki/567

If you can interface to it, you can get the digital readout through the giant circular connectors in the back.
 

Offline Mosaic

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #26 on: May 14, 2016, 01:18:43 PM »
Most of those older sampling gear are entirely out of cal. and are made of unobtainium. Often they require separate/additional equipment for triggering.

Of course I don't mind having one, since I like old gear, esp. the versions where there's a service manual.

But this thread isn't about buying vintage gear or everything becomes a moot point.




 

Offline Earendil

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #27 on: May 14, 2016, 08:14:24 PM »
These instruments typically have self-calibrating timebases. They even calibrate themselves during measurement sometimes, unless you switch that mode off. You can also calibrate the sampling heads semi-automatically. You just need to connect the sampling head to scope's calibrator output and then to a short.

Most of those older sampling gear are entirely out of cal. and are made of unobtainium. Often they require separate/additional equipment for triggering.

Of course I don't mind having one, since I like old gear, esp. the versions where there's a service manual.

But this thread isn't about buying vintage gear or everything becomes a moot point.
« Last Edit: May 14, 2016, 08:17:47 PM by Earendil »
 

Offline Mosaic

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #28 on: May 15, 2016, 03:11:23 AM »
Let's not make this a discussion of vintage equipment capabilities as opposed to doing something of value today with readily available parts and techniques.
There are enough forums for vintage eqpt chat and comparisons.
If you believe 20, 30 , 40 and 50yr old vintage eqpt don't need calibration and self calibrate ad infinitum implying that components & connectors don't degrade and drift then that is a discussion for another thread. I won't comment on this one way or the other.

 

Offline Alex Eisenhut

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #29 on: May 15, 2016, 03:17:03 AM »
Let's not make this a discussion of vintage equipment capabilities as opposed to doing something of value today with readily available parts and techniques.
There are enough forums for vintage eqpt chat and comparisons.
If you believe 20, 30 , 40 and 50yr old vintage eqpt don't need calibration and self calibrate ad infinitum implying that components & connectors don't degrade and drift then that is a discussion for another thread. I won't comment on this one way or the other.

It's a zombie project, in 2013 I put up a google spreadsheet for a 1GHz sampler and it fizzled out. It's just too niche of a thing, and people like me who buy vintage samplers just to see the fastest rise-time are already in possession of what they want.
 

Offline Mosaic

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #30 on: May 15, 2016, 03:24:35 AM »
You have a link for that Alex?
 

Offline Alex Eisenhut

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Offline Earendil

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #32 on: May 15, 2016, 03:30:56 AM »
It's you who raised the topic of "vintage" equipment and made ridiculous claims about these high-end instruments.

And I don't believe these instruments can self-calibrate. I know. Because I have these stuff.
E.g.: http://www.eevblog.com/forum/testgear/40-ps-rise-time/msg935430/#msg935430

Let's not make this a discussion of vintage equipment capabilities as opposed to doing something of value today with readily available parts and techniques.
There are enough forums for vintage eqpt chat and comparisons.
If you believe 20, 30 , 40 and 50yr old vintage eqpt don't need calibration and self calibrate ad infinitum implying that components & connectors don't degrade and drift then that is a discussion for another thread. I won't comment on this one way or the other.
 

Offline Earendil

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #33 on: May 15, 2016, 03:43:48 AM »
Also it seems quite obvious to me that you trying to make money on this. I normally wouldn't care about it but I don't like if someone try to mislead others. Sampling oscilloscopes are very specialized and for everyday use they aren't useful at all.
Without having a picosecond rise time pulse generator you can basically use these only to look at eye-diagrams. And that's it.
You can't decode any data. Also you can't even look at the eye-diagrams of serial communication protocols (like USB) because you need a clock to trigger on. But that's implicit in modern serial communication standards.

It's you who raised the topic of "vintage" equipment and made ridiculous claims about these high-end instruments.

And I don't believe these instruments can self-calibrate. I know. Because I have these stuff.
E.g.: http://www.eevblog.com/forum/testgear/40-ps-rise-time/msg935430/#msg935430

Let's not make this a discussion of vintage equipment capabilities as opposed to doing something of value today with readily available parts and techniques.
There are enough forums for vintage eqpt chat and comparisons.
If you believe 20, 30 , 40 and 50yr old vintage eqpt don't need calibration and self calibrate ad infinitum implying that components & connectors don't degrade and drift then that is a discussion for another thread. I won't comment on this one way or the other.
 

Offline Mosaic

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #34 on: May 15, 2016, 04:08:32 AM »
Earendil:
Please refrain from commenting on my thread. Your comments clutter constructive efforts. :--
Thanks for understanding.

You are self contradictory. Since, as you say,  this is a niche item and I am hoping to achieve it for a small investment, it's not about making money.

« Last Edit: May 15, 2016, 04:14:08 AM by Mosaic »
 

Online Marco

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #35 on: May 15, 2016, 04:20:07 AM »
Some low ball GHz range sampler isn't too interesting. But a double digit GHz range sampling oscilloscope with TDR could be handy at low enough cost, especially for the TDR. Parts wise it could be done very cheap, especially if you avoid the boring high speed ICs.

This guy made a pulser with a rise time which is the near equal of integrated GaAs NLTL shock lines pulsers, he did it on a 2 layer FR4 board for a couple dollar in parts with rivets used for via stitching ... it's only let down in fall time because of the large dimensions of his CPW differentiator.
 
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Offline Earendil

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #36 on: May 15, 2016, 04:22:17 AM »
Don't worry. I won't comment anymore since you never really answered any of the issues I raised. I  see no point of arguing with someone who just evades the questions without addressing the fundamental issues.
I'm off.

Earendil:
Please refrain from commenting on my thread. Your comments clutter constructive efforts. :--
Thanks for understanding.

You are self contradictory. Since, as you say,  this is a niche item and I am hoping to achieve it for a small investment, it's not about making money.
 

Offline KE5FX

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #37 on: May 15, 2016, 05:19:25 AM »
Some low ball GHz range sampler isn't too interesting. But a double digit GHz range sampling oscilloscope with TDR could be handy at low enough cost, especially for the TDR. Parts wise it could be done very cheap, especially if you avoid the boring high speed ICs.

This guy made a pulser with a rise time which is the near equal of integrated GaAs NLTL shock lines pulsers, he did it on a 2 layer FR4 board for a couple dollar in parts with rivets used for via stitching ... it's only let down in fall time because of the large dimensions of his CPW differentiator.

That's really interesting.  I've never heard of a step-recovery effect in ordinary bipolar transistors.  Usually they're operated in avalanche mode in this type of circuit, but he's only using 5 volts to power the whole thing.

I also like his construction technique -- CPW on a homebrew PCB with rivets (?) as vias is another cool trick I haven't run into before.
 

Online Marco

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #38 on: May 15, 2016, 05:36:42 AM »
That's really interesting.  I've never heard of a step-recovery effect in ordinary bipolar transistors.  Usually they're operated in avalanche mode in this type of circuit, but he's only using 5 volts to power the whole thing.

I also like his construction technique -- CPW on a homebrew PCB with rivets (?) as vias is another cool trick I haven't run into before.

The method from this paper. A paper which deserved much more attention than it has had. I suspect there is a parallel to the DSRD diode effect because the way the transistor is driven is very similar (it's not simply taken out of saturation to create the pulse, but only driven into saturation for a short period before being turned off again).
 
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Offline Mosaic

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #39 on: May 15, 2016, 06:07:02 AM »
Some low ball GHz range sampler isn't too interesting. But a double digit GHz range sampling oscilloscope with TDR could be handy at low enough cost, especially for the TDR. Parts wise it could be done very cheap, especially if you avoid the boring high speed ICs.

This guy made a pulser with a rise time which is the near equal of integrated GaAs NLTL shock lines pulsers, he did it on a 2 layer FR4 board for a couple dollar in parts with rivets used for via stitching ... it's only let down in fall time because of the large dimensions of his CPW differentiator.

Yes. But I don't have a sampling scope, but I am hoping to obtain a TDS694C 3Ghz, 5Vrms  real time scope. I have one being calibrated by a vendor now, which I'll buy if it cals on all 4 channels.
Then use that as the basis for 1 to 3 Ghz sampling pulse design. Gain skills/abilities/ experience and then go for the improved TDR level capable units.

Also just got a  60's era model 3300 Alford slotted line with all parts as a means of crosschecking propagation and impedances. I do have a 3Ghz VNA with SOL cal kit and a 3Ghz noise figure analyzer with cal'd noise source.

I can get a Tek 7854 with TDR 7S12 and sampling/pulse heads for about $400. Having problems locating a 7T11/A triggering plugin tho. |O

I love vintage Tek and HP/Agilent gear. (got 3 x 2465X scopes and  all the TM500 req'd calibration plugins). But I also love designing new things as I learn by doing. I forget half the theory stuff I learned from MIT  EE now and I still use my HP28S RPN programmable 32Kbyte  calculator from 1987!

I do appreciate all the links & papers shared so far and I'll keep updating the dropbox link with  them so its a general resource for anyone interested. :-+




 

Offline LaserSteve

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #40 on: May 16, 2016, 11:28:02 PM »
Lets be practical a moment, shall we?

     She Whom Must be Obeyed/Honored has cut my new gear space allocation to near zero..   I thus must go the home-made  sampling route rather then buying big boxen that take up gear space..  She also does not understand taking risks on Ebay, but will allow new construction as she can sit with me while I solder... And she is handy with a wrench. No, I'm not THAT whipped, but she does have a point about my owning more then enough gear now..  Especially since she'd like to see my car fit into the other side of the garage, rather then see it piled with more gear....

     As I work on sampling phase detectors for 10 and 24 Ghz ham radio, having a 1.5 Ghz scope is more then enough to view my sampling gate signals.  Unlike the naysayers who think "free running" scopes are an abomination, I know the limitations, but really enjoy using the sampling method.  MY friend has a pile of Tek sampling gear, but his is an hour and a half away..  Not to mention his "SWMBO", who is an engineer,  wants him to spend more time on their family, and I don't blame her..  So I'd like my own sampler, and I know how to use it...

    Damn, If I could have found the ideal mate, the conversation would have been like this:   "Honey, I think we need a new Oscilloscope...  I'd like to get a 1 Ghz scope.." No Dear Heart, One Ghz is far too slow, would it not be more economical to just get the 2 Ghz now, Because next year you'll need to upgrade anyway.  Besides, I have a 20% off coupon for Lecroy." 

Instead I'm dating a Librarian...

      So lets not derail this with discussions of Tek and HP's past glory, which contain un-obtainium  custom parts from when they had their own fabs...

    Some day, some of you will be in EXACTLY the same place I am now... Enjoy it while your young and single and can blow a whole paycheck on a cool toy... And marry wisely, find a supportive  one who can/will tolerate and encourage  your need for hardware and hording parts...

 I'm still trying to explain to Her why I own a full size milling machine... Thank God for a guy from church who agreed to host it in his warehouse...

Steve




« Last Edit: May 16, 2016, 11:36:30 PM by LaserSteve »
 

Offline LaserSteve

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #41 on: May 17, 2016, 02:36:18 AM »
As I am working at RF, I bought three of these sampling phase detectors, but would like to extend down to DC... And "UP" to pulses...

http://www.ebay.com/itm/131608328730?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I convinced the seller to break the auction from whole lot to singles..

Steve
« Last Edit: May 17, 2016, 02:39:09 AM by LaserSteve »
 
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Offline Mosaic

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #42 on: May 17, 2016, 03:31:10 AM »
His PDF spec links seems broken.
but I found this gen. ref.
http://www.digikey.jp/en/pdf/s/skyworks-solutions/skyworks-sampling-phase-detector
 

Offline rfeecs

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #43 on: May 17, 2016, 04:04:51 AM »
Another link to the Macom datasheet:
http://www.datasheets360.com/pdf/7844736903451203870

Interesting little module.  I honestly didn't think that a hobbyist could make a fast sampler without being able to handle chip and wire, beam leads, etc.  Maybe with something like that, they could.
 

Online Marco

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #44 on: May 17, 2016, 04:09:42 AM »
It's an interesting component, only needs a relatively slow (but high amplitude) balanced signal to drive the SRD to turn it into a sample bridge (basically figure 3b, the input capacitance of the buffers captures the sampled signal). That said LLNL, proved that even commodity schottky diodes can get up there.

PS. this kind of sample gate has a relatively small range by the way, couple 100 mVpp max.
« Last Edit: May 17, 2016, 04:13:08 AM by Marco »
 

Offline Mosaic

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #45 on: May 17, 2016, 02:23:16 PM »
His PDF spec links seems broken.
but I found this gen. ref.
http://www.digikey.jp/en/pdf/s/skyworks-solutions/skyworks-sampling-phase-detector

I ordered 3 as well, along with a few other mini circuits parts  (mmic amp, 4 GHz- digital step RF attenuators, low pass filter etc etc.) as he has a fair selection.

 

Offline chris_leyson

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #46 on: May 17, 2016, 04:47:21 PM »
Thanks Mosaic, it's going to be an interesting thread.

Funny how both the scopes I use are undersamplers and they get used on a daily basis, HP-54610B and Tek-7854. They each use different methods for capturing signals, the Tek samples both the X and Y channels randomly using a pair of sample and hold amplifiers and single 10-bit ADC multiplexed between X and Y channels. The HP samples Y1 and Y2 and probably uses sequential sampling, I'm still not sure how HP derive their sample timing they weren't giving much away in the HP Journal.

Thanks LaserSteve, those MACOM phase detectors look interesting, nice having the the SRD built in.



 

Offline Earendil

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #47 on: May 17, 2016, 08:38:06 PM »
Mosaic,

Please receive my heartfelt apologies. There's a real need for your sampler. It seems you found your target audience.
I'm a bit stunned by this yet. But it was hell of a learning experience. Not in engineering. But it was very useful for learning something new about the world and the human psyche.
I probably go now and bang my head to my desk for some time.  |O
 

Online Marco

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Re: DIY Ghz sampling head for <100Mhz scopes
« Reply #48 on: May 17, 2016, 11:31:30 PM »
I'm still not sure how HP derive their sample timing they weren't giving much away in the HP Journal.

Dunno about those scopes but the 11800 and it's many successors use the method described in this patent. Found the reference in the 50 Years of RF and Microwave Sampling overview paper. It's a triggered delay line oscillator like Lukas described, but with temperature compensation. Also build with discrete transistors rather than boring expensive ECL ICs :) (In my opinion ECL ICs and ultrafast comparators should be avoided to keep costs down, the most expensive components should be the PCB and the SMA connectors.) The vernier they use for fine grained delay is an IC ... a simple ramp based delay would probably be good enough though, you don't absolutely need 10 fs precision.

For long delays a method using a triggered oscillator is one of two options ... the other option being a ramp based delay with clock based interruption (ie. start the ramp on the trigger, at the next clock edge interrupt the charge/discharge for N clock cycles, then continue the charge/discharge until the level detector triggers).
 
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Offline Mosaic

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