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Re: Issue with nanoVNA-Saver in at least the last several versions.
Alan,
I have done some more investigation of the issue I am seeing to further isolate the cause. Here are the results. For the nanoVNA (2.8" display) I thought sure I had seen the problem with this device; however, at this time I cannot reproduce the symptom of getting 0.0 + j0.0 for an S21 measurement when both input ports (CH0 and CH1) are terminated. I did terminate both ports when performing the isolation calibration. With both ports terminated I see single-scan (50 kHz to 50.05 MHz) S21 values from a peak of about -78 dB to a minimum of about -100 dB. As a result I don't see any issues with indications in nanoVNA-Saver with the S21 values. This is true whether I terminate port 0 or port 1 or both. I see very little change when terminating the ports or leaving them open. In a post above, I attached a file (S21Isolation-nanoVNA.png) showing the result of averaging 20 scans which lowers the noise floor substantially, as it should, when compared to a single scan. The maximum value when averaging 20 scans in nanoVNA-Saver from 50 kHz to 50 MHz in that plot is about -89 dB which is quite impressive. And, the result seems to have a random variation with frequency which is consistent with it being a noise floor. The result above caused me to go back to the nanoVNA-F (4.3" display) to try to verify the exact conditions which cause the issue with it that I showed in an earlier post (the file S21Isolation-Singlescan.png.) Again, I did perform the isolation calibration with both PORT1 and PORT2 terminated in 50 ohms. I just went back and looked at S21 values with no load on either port of the nanoVNA-F. I have attached a plot from nanoVNA-Saver of an example (S21Isolation-nanoVNA-F_noterm.png.) Note that this plot has a maximum value in the single scan of about -82 dB and a minimum value of about -106 dB. In this plot the data does look like random noise which is approximately uniform over the 50 kHz to 50.05 MHz range being tested. In this example, there are no 0.0 + j 0.0 results for S21. And, I very rarely see what appears to be a 0.0 + j0.0 result on the S21 display of the nanoVNA-F when there are no terminations on the input. However, when they are there the device plots the point at the most negative value on the display. It is so rare that I have been unable to capture a 0.0 + j0.0 with no terminations on the device. In order to observe the data in the isolation case on the display I had to set the scale/division to -20 dB/division. I then added a single termination to PORT2. An example plot is attached in the file S21Isolation-nanoVNA-F_termOnPort2.png. In this file I just happened to catch an S21 value of 0.0 + j0.0 at 4.05 MHz. So I also saved the s2p file which is attached as S21Isolation-nanoVNA-F_termOnPORT2.s2p. Looking at this file you see that the S21 value at 4.05 MHz is 0.0 + j0.0. Further we see that nanoVNA-Saver shows S21 gain of 0.0 dB which is clearly not what we want for a 0.0 + j0.0 response from the VNA. With a single termination on PORT2 of the nanoVNA-F, it is very hard to capture such an measurement. Watching the nanoVNA-F display for several minutes, I did not see any more such indications even though a scan is repeated every 2 seconds or so. I was simply lucky to get the result I have attached. Also note that the maximum value of S21 in this plot is still about -83 dB and the minimum is about -120.0 dB at 18.55 MHz. Looking at the s2p file saved from nanoVNA-Saver I observe the reading was 1e-6 -j0.0. I can't be sure of what came out of the nanoVNA-F; however, I think it put out 0.000001 - j0.000000 Since the output from the nanoVNA-F is in ASCII decimal notation with 6 digits to the right of the decimal point, the value reported at 18.55 MHz is literally the smallest value that can be represented other than 0.0 + j0.0. So what may be happening here is a limit on the precision of the representation sent from the VNA to the PC. I then added a termination to PORT1 of the nanoVNA-F with no other changes. Remember, this is the exact same configuration used to calibrate the device for the isolation measurement. A plot of a single scan from the device is attached as S21Isolation-nanoVNA-F_termOnPORT1_PORT2.png. Here we see an S21 value of 0.0 dB at many frequencies at and below 10.05 MHz. I saved the s2p file (S21Isolation-nanoVNA-F_termOnPORT1_PORT2.s2p) for this scan as well. Looking at this file we see 0.0 + j0.0 values at all frequencies below 10.55 MHz except 2.05 MHz, 6.05 MHz, and 9.05 MHz. All frequencies where 0.0 + j0.0 is reported in the s2p file are plotted in the nanoVNA-Saver S21 Gain as 0.0 dB. Those frequencies listed here that are not 0.0 + j0.0 are reporting pretty small amplitudes that are not too far above 1e-6, the minimum value that can be reported in the ASCII stream of data sent to the PC from the nanoVNA-F. On my device with the calibration I created, this type of result is quite repeatable. Every scan with both inputs terminated in 50-ohms will have some values which report as 0.0 + j0.0. What this means, in practical terms, is that the isolation between PORT1 and PORT2 is really good or that the leakage between those ports is very repeatable below about 10 MHz and calibration is removing those values. The 20 scan average shown in the post above (S21Isolation-nanoVNA-F.png) shows a decided lowering of the S21 response with both ports terminated below about 25 MHz. I would not expect this to be a reduction in noise at lower frequencies. It could mean that the leakage signal is more repeatable at those frequencies and isolation calibration is removing repeatable errors. In either case, I really don't think this is a serious problem for practical measurements. This configuration of loads has many more results that are reported as 0.0 + j0.0 from the nanoVNA-F; however, it is also the configuration used in isolation calibration. Interestingly, the values sent to the PC have to be on the order of 0.000010 to 0.000030 for signals down by 90-100 dB. The quantization for these small values cannot have a great deal of precision given that 6 places to the right of the decimal all that is being sent to the PC in ASCII decimal notation. Quantization error can be significant on amplitude and/or phase. I would call this a limitation not a problem to be addressed. The fact that the nanoVNA-F seems to have lower isolation values than the nanoVNA is perhaps a good thing but is, in some ways, being limited by the precision of the data being sent to the PC. Again, I don't see it as an issue but it is a limitation. The creators of the software had to make some choices about the representations they send to the PC once they decided to send it in ASCII decimal format. Choosing 1e-6 as the minimum value to represent is reasonable; however, it does result in potential quantization errors when we are talking about signals that are smaller than the reference signal (the signal being sent out PORT1) by something like 90 to 100 dB. I don't consider this an issue but simply a limitation in the dynamic range that can reliably be measured by the nanoVNA-F device. The real issue is that nanoVNA-Saver is not working with this limitation well when the device sends back 0 + j0.0. It should plot and treat this indication from the nanoVNA differently for ALL S21 measurements and calibration. A relatively simple software fix should be available for Rune to implement. I have not but will try calibrating the isolation measurement using only a load on only PORT2 to see if that changes anything. I'll post the result here as soon as I have time to create the result and evaluate the information. -- Bryan, WA5VAH |
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Re: #nanovna-h4 stops at boot screen
#nanovna-h4
On Wed, Feb 5, 2020 at 02:29 PM, Hans-Martin Kurka wrote:
Nice to hear that you got it working.. Have fun with your new NanoVNA Roger |
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Re: #nanovna-saver Impedance value /Z/
#nanovna-saver
Hello Herb,
unfortunately in that Settings->Marker->Settings..the entry for S11 /Z/ is missing. Howver it exists in DisplaySetting -> Displayed Charts |
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Re: #nanovna-saver Impedance value /Z/
#nanovna-saver
On Wed, Feb 5, 2020 at 01:34 PM, UlrichKraft wrote:
Yes,but it ONLY shows the tradintional formats.in the markers. It is kind of inconsistant, because the graph allows selecting S11 /Z/, but I cannot select that in the markers entries. ================================================ UlrichKraft, See attachment. Go into Display Settings->Marker->Settings... and select the marker display settings that interest you. - Herb |
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Re: Which Chart(s) for Which Measurement(s)
On Wed, 5 Feb 2020 at 19:35, Chuck Carpenter <w5usj@...> wrote:
Thanks See this IEEE article on return loss or if you don¡¯t have an account, use sci-hub. Post the above URL into with a bit of luck, the following link might work. Unfortunately, despite their own editor writing some time ago that the return loss should be positive for a passive device, the IEEE regularly publishes papers with negative return loss values. -- Dr. David Kirkby, Kirkby Microwave Ltd, drkirkby@... Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom |
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Re: Which Chart(s) for Which Measurement(s)
Here's one I've just found in the group files:
20191220_ON7DQ_NanoVNA_Presentation_English.pdf NanoVNA presentation by ON7DQ for the Ostend Radio Club, in ENGLISH It helps by using different combinations of search words...8^) In this case: nanovna-saver charts It's very good as it shows which charts were used for the results demonstrated. -- Chuck, W5USJ |
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Re: #nanovna-saver Impedance value /Z/
#nanovna-saver
1. A specification of R +/- jX provides the exact value.
You cannot calculate back this exact value from |Z|. 2. You are free to use the Pythagorean theorem to calculate |Z|. 3. You cannot follow every specific request of a user, that would inflate this project immeasurably. |
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Re: #nanovna-saver Impedance value /Z/
#nanovna-saver
Yes,but it ONLY shows the tradintional formats.in the markers.
It is kind of inconsistant, because the graph allows selecting S11 /Z/, but I cannot select that in the markers entries. So I'm asking ift hat could somehow be added ? Unfortunately I'm not familiar with Phyten at all..... |
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Re: Which Chart(s) for Which Measurement(s)
BTW, I've always understood(?) that Return Loss is a negative number. Some agree other say its a positive #. Display Settings has option selection for either.============= Well, if it is a LOSS, the correct way is to express it as a positive number. Using a negative number would imply that you are expressing a GAIN... 73? Alberto? I2PHD |
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Re: Portable full 2-port 6 GHz VNA from YL3AKB
On 2/5/20 10:41 AM, Alberto I2PHD wrote:
???? I don't currently have any gear that will hit 6 GHz, but I hope to get on some of the ham bands that high and higher, soon. So, I would like to have that capability, and higher.? On the other hand, while I currently could afford to spend a bit more than many hobbyists on a VNA and other gear, that's only because I recently received a small inheritance.? In the past I have found myself in the "50 bucks is all I can spend on a VNA" category, and I suspect I will be back there relatively soon.? So I certainly understand those who say keep the price down!? So, to Gabriel and others working on improved VNAs, do the best you can, and I know you will. |
Roger Need
Dr. David Kirkby, Kirkby Microwave Ltd
Chuck Carpenter
Wolfgang Kiefer
Alberto I2PHD
Jim Allyn - N7JA