SVA1015X - comparisons with HP 8753  - Page 1
Forum section: electronics / testgear

author: hendorog
author_rank: Super Contributor
timestamp: July 28, 2018, 09:45:28 am
content: I've got hold of tautechs SVA1015X at the moment, for a bit of a play.I made a couple of filters quite a while ago, which I though would be interesting to test, and compare the results to my HP 8753.First pic is a 137 MHz HPF which I made to try and get a weather satellite receiver to work. I wanted to knock down the FM broadcast stations a bit, so it needed to block 108MHz, and pass 137MHz.Second pic is a 1GHz LPF which is needed for the HP 8753 alignment process.Firstly, it has to be said that the VNA mode on the SVA is very basic at the moment. Clearly the intention is to enhance it, as some options in the UI are greyed out. It works well even with the limitations, but there are some caveats.The main issue I found was the return loss on the ports isn't great, and the VNA software doesn't yet support a full 2 port calibration. It just has Response calibration.This means that the return loss of the ports cannot be 'calibrated out' when measuring S21. It can be calibrated out when measuring S11 (return loss or VSWR) as the SVA does support OSL 1 port calibration.To reduce the effect I inserted a 20dB attenuator on Port 2 before calibrating. I found that gave good results. Without the attenuator there was quite a bit of ripple in the S21 traces.Stuff that is currently missing is:* IF bandwidth can't be set in VNA mode.* Number of points can't be adjusted. So it always takes about 5 seconds to get a trace no matter how wide the span.* No trace math in VNA mode.* Can't reduce dB/Div below 1dB/div.* Can't select Cal Kits - I've looked on the flash and there is only one Cal kit defined.- However you can edit the definition files to match your cal kit if you telnet in. They are just CSV's and list the reflection coefficent at each frequency. That is pretty cool and is better than the traditional method, which uses a model of the standards instead of their measured properties.* Traces aren't configurable like they are in SA mode. There are only two traces in VNA mode, not four.* The reference level and reference position are a single setting which is a bit odd. You set the reference level to be the dB level you want at the middle of the screen. It does the same thing as the HP, but isn't very intuitive.* Lower limit of VNA mode is 10MHz. This might be a temporary limitation to reduce issues, as the hardware is capable of going lower than that.* Sweeps are quite slow, about 5 or 6 seconds. I think this is a side effect of the 'switching' architecture. It has to measure at least one test port, and the TG output at each frequency step using a single signal path and ADC.* Only one trace is updated at a time, even when two are displayed on screen.* There isn't a way to display both traces and choose which trace will be updated. When two traces are displayed then trace two is always live and trace one is always view only. When one trace is displayed then trace one is live and trace two is hidden.The only bug:* Occasional glitches in the trace - you can see one of these on Daves video. These sometimes trip the ADC overload warning buzzer.All in all the hardware capability seems good. The software is pretty basic though and hopefully will be improved reasonably soon.

author: TheSteve
author_rank: Unknown
timestamp: July 28, 2018, 05:09:46 pm
content: I don't think it can ever do a full 2 port cal can it? I thought it had no source for port 2 so really all it can do is OSL on port 1 and then normalize port 2. This would be how many other "economy" analyzers function like an HP 8752C, the 8711/8712/8713/8714a/b/c and a N9912A FieldFox as far as I understand.

author: hendorog
author_rank: Super Contributor
timestamp: July 28, 2018, 07:33:50 pm
content: Quote from: TheSteve on July 28, 2018, 05:09:46 pmYou are right - what I meant to say was it needs 'one path two port'. My 8753 has this option. I found this doc and it is also called 'Enhanced Response' calibration.Then you can measure everything a full vna can measure. The idea is that you use the human to reverse the dut instead of having an s param test set do it automatically.http://na.support.keysight.com/pna/help/latest/S3_Cals/Select_Cal.htm

author: TheSteve
author_rank: Unknown
timestamp: July 28, 2018, 07:56:10 pm
content: Perhaps it can't, does it measure S21 phase?

author: hendorog
author_rank: Super Contributor
timestamp: July 28, 2018, 08:06:04 pm
content: Quote from: TheSteve on July 28, 2018, 07:56:10 pmYes it does - which makes sense as it is just one receiver doing all of the measurements for all of the ports (The internal TG, Port 1 and Port 2).So its much more capable than something like a Cable Analyser, which might have a power meter on port 2.

author: hendorog
author_rank: Super Contributor
timestamp: July 29, 2018, 01:43:37 am
content: Here is a pic showing how well the 137 MHz HPF blocks the FM broadcast band.Measured on the SVA in Spectrum Analyzer mode with Max Hold on.This is with a random bit of wire as an antenna.

author: hendorog
author_rank: Super Contributor
timestamp: July 31, 2018, 07:16:45 pm
content: Quote from: hendorog on July 28, 2018, 07:33:50 pmCorrecting myself here. One path two port and Enhanced Response calibration are not the same thing.Enhanced Response came along later. I am not alone as many people have confused these cal types over the years.This paper has a very good explaination of the pros and cons of each cal type and the equations which need to be solved:https://www.inti.gob.ar/electronicaeinformatica/metrologiarf/pdf/Incomplete2-PortVNACalibrationMethods.pdfQuoteIt is a absolute no-brainer to build this cal type into a modern T/R analyzer.Why haven't they already implemented it? The only logical explaination is Siglent don't understand what it could do for them.

author: hendorog
author_rank: Super Contributor
timestamp: June 18, 2019, 08:17:13 pm
content: I had a look at the new firmware on tautechs SVA, and it is much improved. Most of the issues I listed are addressed.And there is a new greyed out option on the Cal screen "Enhenced Response"- yep thats a typo, but the important thing is that it is going to be implemented.I think we found a couple of bugs in the new stuff though:* After doing a user SOL cal for S11 on a frequency range, the measured return loss of the load used for the cal was worse (trended up by about 10dB) at the left end of the screen. Repeating the cal with a different frequency range showed the same thing.* The VNA maths didn't seem work the same way as on the HP models. Hitting trace -> mem and then showing trace-mem and trace/mem resulted in a trace at 0dB and 1dB RL when I think they should be showing a large -ve number and 0dB respectively.I didn't use it for very long, so I am not certain that the issues were not user error. Regardless, they have certainly made big strides on the VNA functionality.