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Re: Advice sought on specific measurement.
I did something similar a couple of years ago when type N "connector savers" were offered from China. These are male to female adapters. The first batch wasn't very useful about about 1.5 GHz. The second batch, from the same vendor were much better, working well to about 4 GHz. No idea why that was. They looked identical. I use APC-7 connectors, so your research is interesting to me.
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Stuart K6YAZLos Angeles, USA -----Original Message-----
From: Reginald Beardsley via Groups.Io <pulaskite@...> To: nanovna-users <[email protected]> Sent: Sun, Sep 22, 2019 8:25 am Subject: Re: [nanovna-users] Advice sought on specific measurement. I'm playing with rather more exotic HW, a Tek 11801 & SD-24 TDR head which is a ~26 ps rise time TDR evaluating the quality of Chinese RF connectors.? But the principles are the same and I'm very interested in using the nanoVNA for such things.? I'm a retired seismic research guy, so I've been having a blast. Most fun I've ever had with a piece of test gear and all I'm doing is playing. I look at the time domain S11 and the time domain S21 response.? The S11 TDR shows any discontinuities and the rise time of the S21 TDR gives me an estimate of the frequency limit.? In my case I'm putting the connectors between a couple of pieces of RG402 terminated with SMA-M connectors. If you do an SOLT on a short known high quality cable, then substitute the CUT and repeat the SOLT at the end of the CUT you should get a very accurate picture of cable and connector quality.? In the frequency domain there should be a linear phase shift difference between the reference cable and the CUT.? The ratio of the S21 values should give you the loss. I can't keep up with who's done what on this topic in the nanoVNA FW & SW, but the MATLAB clone, Octave is an ideal tool for taking data via the nanoVNA console and analyzing it.? The frequency spacing determines how long a cable you can test.? 1 MHz spacing will give you the ability to test to 100 m.? The resolution is dependent upon the maximum frequency. So 901 points from 1 to 900 MHz is probably a good choice of sweep parameters.? You'll need to use the reference cable results to compensate for amplitude errors in the nanoVNA.? If you pad lots of zeros on to the end of the frequency domain measurements you will get very fine sampling in the time domain. I recommend doing this with bare uncorrected data at least once using Octave just for the educational experience.? It's actually *very* simple.? And there are plenty of people here able to help out. I used? the 11801/SD-24 to test? another APC-7/N-F adapter yesterday from the same seller as in the photos here: Comments on second sample: I've still got tests of BNCs and other stuff to do with the 11801 and then I'll be duplicating some of the tests on the nanoVNA and my 8753B. Have Fun! Reg |
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Re: NanoVNA Saver
Hi Bryan,
this sounds easy to implement. I'll put it in the next version. :-) -- Rune / 5Q5R On Sun, 22 Sep 2019 at 23:45, bryburns via Groups.Io <bryburns= [email protected]> wrote: Hi Rune, |
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Re: NanoVNA Saver
Hi Rune,
Thank you for this great software for the nanovna. I appreciate the 3 different markers which are available and you readout a lot of good information in the boxes to the left of the graphs. Would it be possible to put the S11 phase in that box in the lower right corner? I don't see a way to readout the actual phase angle except by looking at the S11 phase plot. Am I missing an easy place to get the S11 phase at a particular frequency? Thanks. -- Bryan, WA5VAH |
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Re: Noise
I have one of those blue pcb return loss bridges from Aliexpress. Mine has the resistors correctly bridged. Directivity was measured:
10MHz 55dB (take this number with a grain of salt) 144MHz 39dB 435MHz 29dB 1296MHz 15dB The ferrite binocular cores looks like BN-43-2402. Going back to the nanoVNA bridge discussion, for the bridge to be correctly balanced, besides equal parasitics in both "legs", stimulus source impedance and detector impedance should be equal. I'm not sure what is the Si5351 impedance: last datasheet mentions 50ohm at maximum drive, older datasheets says 85ohm. But nanoVNA uses 2mA (minimum drive) below 300MHz and 8mA (maximum drive) above. Si5351 output impedance will surely depends on the output drive strength, so the bridge performance will not be optimum in some or any of the bands. Ok, the source impedance variation seen from the bridge is atenuated through R22 and R24 divider, but this divider lowers the impedance below 56ohm, much lower than the impedance seen at the bridge detector output. Maybe R24 should be increased. Detector impedance, ignoring PCB traces, and SA612 input impedance (more on this later), is 75ohm. I measured SA612 input impedance from 10 to 900MHz and it's much higher than the specified 1.5K || 3pF per pin to ground. It doesn't affect at all to the bridge. Can't say the same for the other port, it's RL is only about 16dB at 900MHz. To finish, as previously noted by W0LWA, phase noise could also be a limiting factor for S21 measurement dynamic range at high frequency. But i don't know how much is the processed measurement BW. Si5351 phase noise for a 156MHz carrier is about -110dBc/Hz at 5kHz. It doesn't go down until past 100kHz, so there would be no solution other than using a cleaner oscillator. Carlos |
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Re: RX-Port Input Impedance
Hi qrp.dd
Incorrect, that is not a measurement of the CH1 input impedance. The cable between Ch0 and Ch1 create impedance transformation. You need to calibrate at the end of the test cable with a female kit. If done at the end of the test cable with the female female adaptor fitted and then use the male calibration kit you are getting closer, but still as you have removed the female female adaptor you measure inside th NanoVNA, as the measurement plane now is different than the calibration plane, and shifted inwards with a distance equal to the delay/offset equal to the delay of the female female adaptor. Kind regards Kurt -----Oprindelig meddelelse----- Fra: [email protected] <[email protected]> P? vegne af qrp.ddc@... Sendt: 22. september 2019 09:12 Til: [email protected] Emne: Re: [nanovna-users] RX-Port Input Impedance yes, my NanoVNA CH1 also has VSWR=1.3 at 900 MHz. You can measure it by connect CH0 to CH1 with a good quality and short cable. |
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Re: Using nanoVNA to measure the directivity of a directional coupler
Hello hwalker,
Thank you very much for this useful application note. I very much welcome the fact that not only the measuring setup was described in detail, but also the measuring result was evaluated in detail. I think it makes sence to put the contents in a PDF document and copy it in the files section of this group. 73, Rudi DL5FA |
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Re: Firmware with arbitrary scan length
Hi Carlos,
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like Herb said, the latest version of NanoVNA-Saver was due to include averaging - it does now :-) I saw what seemed like significant improvements in readings from data point to data point at the high end of the measurement range, but I don't have the background to be able to quantify it. The software includes the option of throwing away a number of the "worst looking" samples. I've certainly had times where my NanoVNA returned completely bogus data on a single out of several readings, so I decided it was probably good to implement a truncated mean function. I hope you find some use for it. Do give me feedback on it if you try it :-) -- Rune / 5Q5R On Sun, 22 Sep 2019 at 16:23, Carlos Cabezas <eb4fbz@...> wrote:
On professional VNAs, stimulus source is calibrated for flatness on |
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Re: NanoVNA Saver
For those waiting for new binaries: I just published 0.0.11 :-)
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This release brings averaging as a new feature: Press "Sweep settings" to select between running a single sweep (of optionally multiple segments), a continuous (live) sweeping of the range, or to average several sweeps from the NanoVNA. You can configure how many averages to make, and optionally, how many of the sample points to discard, based on which deviate the most from the rest, and are least likely to contribute signal. Also added is a new Resistance/Reactance chart, which shows both the R and X component of R+jX. This brings the challenge of showing two traces for the same data - added is therefore the option of picking a secondary colour for sweeps under "Display settings". There are further improvements to UI sizing, meaning the interface now fits - tightly - on a 1366x768 screen, at least on Windows. A few quality of live improvements made it in: Press escape in any of the pop out windows to close them instantly. The calibration window now shows more clearly when the source of calibration data is loading from a file, and also the number of points loaded. A few crash bugs were fixed. I look forward to hearing feedback from all of you! -- Rune / 5Q5R On Sun, 22 Sep 2019 at 17:14, Mario Vano <mvano@...> wrote:
On Sun, Sep 22, 2019 at 06:09 AM, Mario Vano wrote: |
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Re: Traces and tracks
Torbjorn,
Google looses things in translation at times and traces in English come out as tracks in other languages. Below is a Google translation from one of the Russian boards. "He poured the firmware into his second instrument, configured two right tracks on CH0, then RESET, calibration, SAVE0, all preserved." Meaning" He loaded the firmware on his second instrument, configured the display for CH0 two traces, then performed RESET, calibration, SAVE0 to preserve the configuration upon re-booting. |
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Re: Does anyone know how sensitive the nanovna is to electrostatic discharge?
Dr. David Kirkby from Kirkby Microwave Ltd
On Sun, 22 Sep 2019 at 13:42, Larry Rothman <ac293@...> wrote:
I believe the point that Dave Jones was making, is that the surface resistance of the mats does not have any adverse effects on 99.99% of the measurements one makes. I don't think his aim was to show how good a static dissipative mat was - only that it does not have any adverse reactions. It's generally considered unsafe to ground the mats - instead they should be connected to ground by via a high-value resistor - typically 10 M ohm. I personally don't think people need to worry about static on the test ports of the NanoVNA. However, since the sides of the NanoVNA are open in the standard unit, then there's a possibility of static doing damage there. Dave |
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Re: Firmware with arbitrary scan length
Carlos
The nanoVNA has about 5 to 10 dB headroom in S21 in alle ranges. This is done by adjusting the gain off the amplifier before the adc to the frequency range Biggest concern in overloading are the mixers when SI5351 outputpower is boosted in overtone mode. But this does not happen. A filter before the amp in the adc keeps near harmonics out. So when measuring amplifiers you always should use an attenuator The design of the nanoVNA is not bad. |
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Re: Advice sought on specific measurement.
I'm playing with rather more exotic HW, a Tek 11801 & SD-24 TDR head which is a ~26 ps rise time TDR evaluating the quality of Chinese RF connectors. But the principles are the same and I'm very interested in using the nanoVNA for such things. I'm a retired seismic research guy, so I've been having a blast. Most fun I've ever had with a piece of test gear and all I'm doing is playing.
I look at the time domain S11 and the time domain S21 response. The S11 TDR shows any discontinuities and the rise time of the S21 TDR gives me an estimate of the frequency limit. In my case I'm putting the connectors between a couple of pieces of RG402 terminated with SMA-M connectors. If you do an SOLT on a short known high quality cable, then substitute the CUT and repeat the SOLT at the end of the CUT you should get a very accurate picture of cable and connector quality. In the frequency domain there should be a linear phase shift difference between the reference cable and the CUT. The ratio of the S21 values should give you the loss. I can't keep up with who's done what on this topic in the nanoVNA FW & SW, but the MATLAB clone, Octave is an ideal tool for taking data via the nanoVNA console and analyzing it. The frequency spacing determines how long a cable you can test. 1 MHz spacing will give you the ability to test to 100 m. The resolution is dependent upon the maximum frequency. So 901 points from 1 to 900 MHz is probably a good choice of sweep parameters. You'll need to use the reference cable results to compensate for amplitude errors in the nanoVNA. If you pad lots of zeros on to the end of the frequency domain measurements you will get very fine sampling in the time domain. I recommend doing this with bare uncorrected data at least once using Octave just for the educational experience. It's actually *very* simple. And there are plenty of people here able to help out. I used the 11801/SD-24 to test another APC-7/N-F adapter yesterday from the same seller as in the photos here: Comments on second sample: I've still got tests of BNCs and other stuff to do with the 11801 and then I'll be duplicating some of the tests on the nanoVNA and my 8753B. Have Fun! Reg |
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Re: NanoVNA Saver
On Sun, Sep 22, 2019 at 06:09 AM, Mario Vano wrote:
CORRECTION: (I mistyped) - The multi-band dipole is my 20ft high 40/20 meter trap dipole that has been augmented with parallel dipoles for 15 and 10. The feedline has a toroid common mode filter.
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Re: Firmware with arbitrary scan length
On professional VNAs, stimulus source is calibrated for flatness on factory with a bolometer. On nanoVNA you can't control stimulus output power, so we should probably calibrate the audio codec gain to get most of it's dynamic range at each frequency, or at least for each band. However multiple mixing products, others than the desired one, could be present at audio frequencies, so this must be done with care.
This could also lead to a debate about needed headroom to measure DUTs with gain. IMHO, it would be better to sacrifice having a lot of headroom and just insert an attenuator if an amplifier S21 is to be measured. I have not taken a look to the code in much detail yet, maybe this is being done, but probably not. I have read somewhere that people have measured their LNA's gain, so current code must be setting the codec gain too low if it has so much headroom and the S21 70-80dB noise floor we are seeing could be in fact being limited by the codec dynamic range. I also miss an averaging mode, as some measurements are quite noisy, and it would help for duplexer adjustments with notches near the VNA noise floor. Maybe just a moving average low pass filter with just 2 taps to avoid increasing memory requirements (new=0.9*last+0.1*meas). David mentions using averaged measurements for isolation, and in fact most professional VNAs use averaging when performing calibration. Carlos |
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Re: NanoVna Menu Scroll Switch Repair Replacement?
It's been my experience what I've had problems with a vendor that they beg you to
give them a positive report if they fix the problem. And generally they will jump through hoops to do it. Have a conversation with the vendor and take your choice, a replacement or a refund. But DON'T give feedback until the issue is resolved. Bruce, K4TQL |
Kurt Poulsen
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