I'll give it a try
Thank You
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Re: TDR setup for NanoVNA #tdr, add electrical delay
This related to points count, old fw have 101 points and use 256 FFT.
Now used 401 points, and 512 FFT
Also added amplitude compensation (for 256 FFT need use 256 points, for 101 points all others filled by zero)
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I read somewhere that if you use the nanoVNA alone you MUST calibrate on it, whereas if you use it attached to nanoVNA-saver, you MUST calibrate on the computer software.
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On Oct 15, 2021, at 7:50 AM, AE5SB <snidrv@...> wrote:
Do I need to do both?
I only did the nanovna calibrate
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Re: TDR setup for NanoVNA #tdr, add electrical delay
Well, couldn't edit the other post so I'm adding this one. I think I figured it out, you have to change the sweep points to 101 or 201.
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Do I need to do both?
I only did the nanovna calibrate
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Re: TDR setup for NanoVNA #tdr, add electrical delay
Just wondering, something seems different with the TDR workings in the latest firmware. In the 0.5.0 fw if you set the frequency to 100 MHz you had your max cable length on the right side was close to 150 to 200 feet, and a flat linear ch0 trace until you hit the end of the cable. Now this fw seems like you have to jack the frequency way up to get that cable end to move towards the right, and the trace is all kinds of up and down, it's not huge jumps but it's not almost flat like it used to be. This is a pic of what it used to look like on 0.5.0. I'll have to take another pic tomorrow to show what the new fw looks like in transform set up the exact same way.
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Re: Is the phase angle displayed on the nanoVNA a measurement of the phase relationship between voltage and current in the DUT?
On Thu, Oct 14, 2021 at 10:55 AM, Gregg Messenger wrote: Are they related? Is WHAT related?
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Re: Is the phase angle displayed on the nanoVNA a measurement of the phase relationship between voltage and current in the DUT?
"Things can be explained simply and clearly if one chooses to do so . Often times, I find it's best to only use as much complexity as is necessary to sufficiently convey one's thoughts." That's exactly what I tried to do in my nanoVNA presentation. Yes, there are quite a number of formulas, but only those that are really needed. see /g/nanovna-users/files/Presentations/20191220_ON7DQ_NanoVNA_Presentation_English%20V2.03.pdfS-parameters are explained in just three slides (18-20), couldn't make it much shorter than that ;-) Luc ON7DQ
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Karl Jan,
My SAA-2N measures about -12dBm at 8MHz CW, but the signal pulses on and off during the sweep. (It is -12dBm during the on times, measured with an HP8563E SA.)
I am using the Ojisan version of the SAA-2 firmware.
--John Gord
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On Thu, Oct 14, 2021 at 10:38 AM, Karl Jan Skontorp wrote:
I'm still struggling with my faulty nanoVNA SAA-2N :-( In addition to the
SAA-2N I have got a nanoVNA-F, a nanoVNA-H4 and a small "very tiny...". The
other units are working ok, but I really want to get my SAA-2N back in
business! Today I tested the S21 measurements with the SAA-2N. I measured a
18MHz bandpass filter, and the unit seems to work ok in this mode :-)
The next thing I wanted to check was the level of the "output signal" on Port
0. I also have a handy spectrum analyzer, the tinySA. I put the SAA-2N in "CW
mode" at a frequency of 8MHz. Connected the tinySA and observed a lot of
harmonics, but the "main peak" was at about -23dBm!!! I think this level is
too low! I did the same measurement on the H4 - result -8dBm and the
nanoVNA-F had +3dBm. The result on the "very tiny..." was -7dBm.
When putting this together, I my first thought was the Si5351, but when I have
done the rest of the measurements, I think one of the RF-switches, MXD8641,
must be broken. Can someone please tell me if my assumptions correct?
Will be grateful for any response!
Karl Jan - LA3FY
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For swr plot you can use the value of 6:1 each side of center freq. Find those 2 values of freq, find their difference and divide into the center freq to get operating Q. If you double that value, that should be close to your so called design Q.
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"the logmag is extremely narrow and touchy to be resonant"
Yes, that one. And you should be seeing a pretty decent return loss value.
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You will be measuring S11, a one port measurement. Set the display for log magnitude dB. So the sweep should show an excellent return loss at the desired frequency set for the PI MATCH, say 7.1 MHz for the 40 meter band. The value of the return loss might be 20 dB or better, it will be clearly a notched like response. See the picture of what I obtained on my amplifier. Your sweep should be similar. I think I was running the sweep over a span of 5 or so MHz at 7, or 5 to 9 MHz for the 40 meter band.
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Re: Is the phase angle displayed on the nanoVNA a measurement of the phase relationship between voltage and current in the DUT?
That¡¯s a good way to put it Roland.
Thanks for the link.
--
VE6WGM
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Did you calibrate on saver and not just on the NanoVNA?
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Re: two nanoVNA linked for two port setup
On 14/10/21 10:24 pm, Jim Lux wrote: But more curiosity than anything else.? The idea of multiple
simultaneous measurements (no relays) is intriguing.? One could build a
N port analyzer with N sources and N^2 receivers, and choose the
stimulus frequencies carefully so that no two are at the same frequency
at the same time.? If the receiver is a wideband SDR, then conceivably,
the N^2 receivers are implemented in only N pieces of hardware, and the
selectivity is in software. With 16 bit ADCs and some averaging, one
might be able to get 80-90 dB dynamic range, or better. Simultaneous is probably overkill ¡ª particularly because non-linearities would break it ¡ª but yes, a single receiver at each port would make sense. There's no shame in mixing, so long as the clocks are synchronous (easy to do in a single instrument). - Roland 9V1RT
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Re: two nanoVNA linked for two port setup
On 14/10/21 10:14 pm, Jim Lux wrote: What I'd be more interested in, somewhere down the road, is figuring out
whether the NanoVNA (or a similar device) can be used to make
measurements of the S22 of a power amplifier, at higher power (for use
in phased arrays, where there is mutual coupling among the antennas). Questions I've not even begun to think about... (although, yes, directional arrays are things that I expect to want to do at low UHF within the next 12 months). - Roland 9V1RT
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Hi Alan,
OK I have been using for traces. a smith chart, and a swr line, and a log mag,
Smith is well a smith,
the SWR seems broad, where the logmag is extremely narrow and touchy to be resonant with the SWR trace.
What trace should i use to take this measurement you are describing?
Joe
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On 10/14/2021 6:37 PM, alan victor wrote: Hi Joe,
The Q you will measure is the operating Q and that probably is the one you want. That is to say, we have the Q on the plate side of the tube and the Q on the antenna side... that is the 50 ohm side and where you would place the VNA. So, with the pi net properly terminated on the tube plate side, use the vna and measure the return loss from its maximum best case, say 20 db until it drops to within 3 dB of its worse case. That total BW should be the operating BW of the pi net. Its value should be 1/2(Q_tube side+Q_ant side). So for example if the tube side Q were 12 and the antenna side 2, operating Q is 7. Usually the antenna side Q is quite small and the Q operating is set by the tube side Q.
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Re: Is the phase angle displayed on the nanoVNA a measurement of the phase relationship between voltage and current in the DUT?
On 15/10/21 1:55 am, Gregg Messenger wrote: It is easy to come to the conclusion that the S11 phase angle as seen on the nanoVNA (CH0 PHASE 90..) is the relationship in a device under test between the voltage and current in that device, and I once fell down that hole myself. I'd suggest that although use of the NanoVNA should not be limited to those with engineering degrees, it would be helpful for most beginners to at least understand what the S11 and S21 parameters refer to. It seems that many new users have never even heard of scattering parameters, let alone understand what they are about. As usual, Wikipedia has a good high-level article <> on this. Anyone using a VNA ¡ª Nano or otherwise ¡ª would benefit from having read and understood about the first third of that article and perhaps at least skimmed the rest. Trying to use a VNA without understanding this would be a little like trying to drive a car without understanding what speed was, let alone what a speedometer does. It's possible to proceed without this knowledge, sure, but doing so makes life needlessly difficult. - Roland 9V1RT
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I should add, this takes the pi net as a single tuned resonator, that the match at fo is good,say 20 dB return loss and for a lossless network,
S11^2+S21^2=1. See how to get Q from a single tuned resonator by measurement of its return loss.
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Hi Joe,
The Q you will measure is the operating Q and that probably is the one you want. That is to say, we have the Q on the plate side of the tube and the Q on the antenna side... that is the 50 ohm side and where you would place the VNA. So, with the pi net properly terminated on the tube plate side, use the vna and measure the return loss from its maximum best case, say 20 db until it drops to within 3 dB of its worse case. That total BW should be the operating BW of the pi net. Its value should be 1/2(Q_tube side+Q_ant side). So for example if the tube side Q were 12 and the antenna side 2, operating Q is 7. Usually the antenna side Q is quite small and the Q operating is set by the tube side Q.
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Jim Allyn - N7JA
Gregg Messenger VE6WGM