Author Topic: EEVblog #1101 - Siglent SVA1015X VNA Teardown  (Read 7962 times)

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Offline EEVblog

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EEVblog #1101 - Siglent SVA1015X VNA Teardown
« on: July 07, 2018, 08:15:09 am »
Teardown and look at the new $1395 Siglent SVA1015X 1.5GHz Spectrum and Vector Network Analyser
Well, $2000 when you include the actual VNA option :-/

 
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Offline Smokey

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #1 on: July 07, 2018, 12:10:08 pm »
Please hold while I fact check RF stuff with The Signal Path....
 

Online Bud

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #2 on: July 07, 2018, 12:20:28 pm »
So if I estimate correctly, buying the VNA option and a Cal kit will make this puppy double the price. Not such a "low cost" VNA it becomes. As well as the function seems to be rudimentary (the useless FFT feature of rigol scopes comes to mind) and it is yet to be proved it was implemented correctly, such as the math behind it and stuff.
« Last Edit: July 07, 2018, 12:22:23 pm by Bud »
 

Offline Stefan Payne

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #3 on: July 07, 2018, 01:42:35 pm »
Teardown and look at the new $1395 Siglent SVA1015X 1.5GHz Spectrum and Vector Network Analyser
Well, $2000 when you include the actual VNA option :-/
Seems like they put in a Rubycon cap to make dave happy ^^
Right next to it was a lelon cap.
And the other Caps are different as well.

The gunk on PSU is for transport, though one would usually use that for the Coils and not just caps.
And I'd also not worry too much about the manufacturer but the Series...
As for Lelon low ESR caps, something like RXW or RZW would be nice.

As for the Processor board:
Doesn't that also save some layers on the Mainboard??
Like using 6-8 Layers on the module and 2 or 4 on the main PCB.
That would be my guess why they are doing it.
« Last Edit: July 07, 2018, 01:45:57 pm by Stefan Payne »
 

Offline EEVblog

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #4 on: July 07, 2018, 01:48:08 pm »
As for the Processor board:
Doesn't that also save some layers on the Mainboard??
Like using 6-8 Layers on the module and 2 or 4 on the main PCB.
That would be my guess why they are doing it.

Potentially, but I doubt that's the main or only reason.
 

Offline jeremy

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #5 on: July 07, 2018, 01:54:12 pm »
Why are the signal traces exposed in only some parts of the RF section, and other parts are under soldermask? Is it so that they can be probed?
 

Offline EEVblog

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #6 on: July 07, 2018, 02:40:32 pm »
Why are the signal traces exposed in only some parts of the RF section, and other parts are under soldermask? Is it so that they can be probed?

No. It's because they are critical transmission lines, and it's easier to control the impedance of a PCB transmission line when it doesn't have solder mask (with it's relatively high variability) mucking up the equation.
 

Offline TheSteve

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #7 on: July 07, 2018, 03:56:39 pm »
Dave - when touring the user interface did you happen to notice if you can enter custom cal kit parameters? I see there was a greyed out ECAL option but don't recall seeing anywhere to enter your own parameters.
VE7FM
 

Offline EEVblog

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #8 on: July 07, 2018, 04:22:20 pm »
Dave - when touring the user interface did you happen to notice if you can enter custom cal kit parameters? I see there was a greyed out ECAL option but don't recall seeing anywhere to enter your own parameters.

Didn't notice anything, but wasn't deliberately looking for that. Not at the lab so can't check.
 

Offline jeremy

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #9 on: July 07, 2018, 04:48:18 pm »
Why are the signal traces exposed in only some parts of the RF section, and other parts are under soldermask? Is it so that they can be probed?

No. It's because they are critical transmission lines, and it's easier to control the impedance of a PCB transmission line when it doesn't have solder mask (with it's relatively high variability) mucking up the equation.

But why is some of it under solder mask then?
 

Offline EEVblog

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #10 on: July 07, 2018, 04:50:44 pm »
But why is some of it under solder mask then?

That part was less critical to the performance, i.e. variability wouldn't have mattered as much.
Notice how the distributed element filters are all exposed, it's because they need controlled performance on those.
 

Offline PA4TIM

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #11 on: July 07, 2018, 06:29:18 pm »
The soldermask has to do with transmission lines. A trace is just a trace for DC but not for RF. There has to be two "traces" one of them the groundplane, the other the trace. Everything in between, nearby or above it makes part of the line.A transmission line has a constant impedance. A soldermask is part of the transmission line but has more loss as air and is not so easy to control over a wide bandwidth. http://www.gsm-modem.de/M2M/m2m-faq/transmission-line/

A SA + TG is a scalar analyser. I sources a signal and measures the insertion loss (the attenuation) There is some delay between the sourcing and measurement. Caused by the instrument and the DUT.  For serious RF work a big no-no.
A VNA measures the sourced signal direct at the source and at the same time the result after the DUT. It needs 2 receivers for that. That gives the real  attenuation and fase difference both at the same time. So the measured fase difference is only caused by the DUT. This is important but the why is a bit much to write in one post. A simpel example is a resonance. At the resonant frequency the fase jumps 180 degrees. So without phase info you are not sure is there is resonance and what is the exact frequency. You need phase info to see if something is capacitive or inductive (and you can calculate all kind of info from that) things that are impossible to do on a scalar analyser.

One of the most important and critical things for a VNA is calibration. On an SNA you can come a long way with simple normalisation. The result of a VNA is totally depending upon calibration and so on the used call kit. A good call kit comes with data. You need to feed that data to the VNA so he knows what you use for calibration. The details are very complex to explain. See it like this. Suppose the VNA calibration kit load is 60 ohm and 1 uH (complete bogus values). I connect it to the VNA and do a calibration run without telling him the specs. If I now connect a perfect 50 ohm with zero inductance the VNA will tell me the resistance is 40 ohm and capacitive (these are not correct values but it makes more clear what calibration is about) Call kits from R&S or Keysight cost more as the Siglent. You can make your own but need a calibrated VNA to extract the parameters. A good call kit has those documented but a VNA is only usable if you can enter those values. Old VNA could not do that so you needed an almost perfect call kit (even more expensive)   and things like line strechters to make sure the signalpath to the DUT was as long as that to the reference receiver.

I just repaired a R&S 4GHz VNA. It is something like 30-40 kilo, huge in size and only to get the powersupply out I had to remove over 80 srews. Everything is covered with metal. All interconnections are rigid coax (low loss and more stable impedance as movable coax cable).
See here for the way that is build:
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Offline jeremy

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #12 on: July 07, 2018, 07:07:19 pm »
That part was less critical to the performance, i.e. variability wouldn't have mattered as much.
Notice how the distributed element filters are all exposed, it's because they need controlled performance on those.

Yep, I understand that the dielectric constant matters for the filters, but I guess I’m just a bit confused why those straight sections in the photo are unmasked whereas there are large chunks that are under mask; the straight sections aren’t filters and they don’t seem to be anything other than standard transmission line. The only reason I can think of is to allow for probing during testing. If it does indeed make a huge difference to loss/variability, then why not totally do away with the solder mask along the trace and expose it through the whole signal chain? It’s gold plated after all, so corrosion shouldn’t be an issue.
 

Offline MartinManzinger

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #13 on: July 07, 2018, 11:24:32 pm »
Hi everyone! Can someone give me a hint where I can find the high resolution pictures, that David mentioned?
 

Offline Phil Smith

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #14 on: July 08, 2018, 12:15:39 am »
Hi everyone! Can someone give me a hint where I can find the high resolution pictures, that David mentioned?

Hey!
Like usual, they are on his FLICKR page -
https://www.flickr.com/photos/eevblog/albums/72157692982928880

Cheers, Phil!

PS. Thank you Dave for a awesome video! These spectrum /vector analyzers are so great candidates to be torn down))  8)
 
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Offline NANDBlog

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #15 on: July 08, 2018, 02:09:27 am »
Pricing of options is pretty disappointing. Also, you cannot use it for 2.4GHz stuff.
I guess it could be a good investment for someone working in the ISM band, Lora, 868MHz stuff and others, without the VNA option, if the firmware can be hacked.
 

Offline gardner

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #16 on: July 08, 2018, 04:18:11 am »
It looks to me like the board material is different between the two instruments.  By eye, FR-epoxy vs teflon.  I wonder if some of the discrete component filters are built they way they are because of the difference in the dialectic properties of the board.
--- Gardner
 

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #17 on: July 08, 2018, 06:08:37 am »
It looks to me like the board material is different between the two instruments.  By eye, FR-epoxy vs teflon.  I wonder if some of the discrete component filters are built they way they are because of the difference in the dialectic properties of the board.
The discrete components are more likely the result of the lower maximum frequency compared to the spectrum analyser. But yes, it is too bad it can't reach beyond 2.5 GHz where all the modern communication standards sit. That makes the SVA1015 obsolete straight away.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline NANDBlog

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #18 on: July 08, 2018, 08:43:30 am »
It looks to me like the board material is different between the two instruments.  By eye, FR-epoxy vs teflon.  I wonder if some of the discrete component filters are built they way they are because of the difference in the dialectic properties of the board.
Dave pointed out many times in the video, that the discrete element filters are bigger in the SVA1000, because the frequency is lower. So you need a bigger cap and inductor. So imagine, if all the filters need to be physically bigger, it makes sense to replace that "big" discrete element with an 0402, instead of reorganizing the entire board.
 

Online tautech

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #19 on: July 08, 2018, 11:29:36 am »
So if I estimate correctly, buying the VNA option and a Cal kit will make this puppy double the price. Not such a "low cost" VNA it becomes. As well as the function seems to be rudimentary (the useless FFT feature of rigol scopes comes to mind) and it is yet to be proved it was implemented correctly, such as the math behind it and stuff.
Yeah Bud when you add all the options in it does pump up the price dramatically however it's functionality does cover a lot of bases and it will be interesting to see how well it does them all. Even the touch screen is new in Siglents larger equipment as we've only seen it in SDG***2X (AWG) models.
We'll know soon enough as they are being shipped all over the place right now and there'll be some findings posted in the dedicated thread for these fairly soon.
https://www.eevblog.com/forum/testgear/siglent-sva1015x-1-5ghz-spectrum-vector-network-analyzer-(coming)/
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Offline EEVblog

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #20 on: July 08, 2018, 02:58:08 pm »
But yes, it is too bad it can't reach beyond 2.5 GHz where all the modern communication standards sit. That makes the SVA1015 obsolete straight away.

Not obsolete, it just has a narrower target market. I can imagine plenty of uses for a 1.5GHz VNA.
 

Offline Neilm

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #21 on: July 08, 2018, 08:05:01 pm »
This would only be good enough for pre compliance work if the UUT maximum clock frequency was less than 200 MHz, otherwise the testing has to go up to 5 times the max clock speed.
Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe. - Albert Einstein
 

Offline MartinManzinger

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #22 on: July 08, 2018, 11:33:30 pm »
Hey!
Like usual, they are on his FLICKR page -
https://www.flickr.com/photos/eevblog/albums/72157692982928880

Thanks for the link!

One thing I'm not shure about: To measure the S11 parameter, somehow the reflected signal has to be measured. But simple multiplexing, like sending the testsignal in, then switching and sending the reflected signal to the receiver could not work. Sending and receiving must be carried out simultaneously. Because of that, there has to be a directional coupler. In the picture of the tracking generator, I marked the component in which all three signal pathes ends. But isnt that device way to small for such an coupler?
 

Offline whollender

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #23 on: July 10, 2018, 02:03:33 am »
Hey!
Like usual, they are on his FLICKR page -
https://www.flickr.com/photos/eevblog/albums/72157692982928880

Thanks for the link!

One thing I'm not shure about: To measure the S11 parameter, somehow the reflected signal has to be measured. But simple multiplexing, like sending the testsignal in, then switching and sending the reflected signal to the receiver could not work. Sending and receiving must be carried out simultaneously. Because of that, there has to be a directional coupler. In the picture of the tracking generator, I marked the component in which all three signal pathes ends. But isnt that device way to small for such an coupler?

That does appear to be the directional coupler.  Minicircuits has similar transformer based directional couplers with the Siglent's spec'd VNA frequency range (10MHz - 1.5GHz).

What you have marked as an amplifier in the path to the small connector near the top of the board is actually a forward/reverse switch (PE42553).  Note the symmetrical DC blocking caps with RF traces going to either side of the package from the coupler.

The other part you have marked as an amplifier (in the tracking gen path) is actually a 7 bit digital step attenuator, also from Peregrine Semi (PE43711).

Edit:
Another note about why some of the RF traces are masked and some are not.  In addition to getting more accurate impedance, removing the mask also reduces the loss of the TL segments, so it makes sense to remove it over the relatively long straight sections.  It's not such an issue for short sections, which is why it's not removed everywhere.
« Last Edit: July 10, 2018, 02:08:58 am by whollender »
 
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Offline PA4TIM

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Re: EEVblog #1101 - Siglent SVA1015X VNA Teardown
« Reply #24 on: July 10, 2018, 02:23:33 am »
I would expect a directional bridge under 1500 MHz

About the soldermask over traces , Signal path has a video he shows an attenuator (for higher frequencies) The theory is related  to the reason you do not cover traces.

The discrete filterers is more easy for low frequencies. I made a 25 MHz to 2 GHz sweepgenerator in several bands. For the lowest bands I used caps and inductors. Then "stripline" (a mix of pcb as caps and wire as inductor?), the highest range ( 2 GHz LPF is "microstrip") http://www.pa4tim.nl/?p=2662
www.pa4tim.nl my collection measurement gear and experiments Also lots of info about network analyse
www.schneiderelectronicsrepair.nl  repair of test and calibration equipment
https://www.youtube.com/user/pa4tim my youtube channel
 


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