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Re: Supply noise at higher harmonics
#internals
Using the console command "sample" it is possible to measure the pure reference, refl and thru signal strength.
First picture shows the change over frequency of the reference signals (only look at the changes in level, the absolute levels differ due to some TAPR VNA internals) According to the internal gain setting table in the nanoVNA there is additional gain added as the frequency moves up. These are the vertical jumps, each about 5dB at 300, 600,900, 1200, 1500 and 1800MHz. In total about 45dB gain is added in the audio path to compensate for signal loss and with the 10dB delta between lowest and highest frequencies the delta is 55dB, similar to the 55dB measured with the direct connection to the SA612 so the nanoVNA adc and dsp algorithm do maintain the dynamic range. Next picture shows what happens when you use a clean 5V supply. Much less noise in the reference signal. The weird thing with the reference signal is the increase in strength above 1.5GHz. This could be caused by capacitive coupling in the attenuator before the reference mixer Third picture is the change of the amplitude signal (red line) of reflection mixer without anything connected to the SMA CH0 connector, a fairly good open. The change of amplitude over frequency does not show any weird things. The green line shows the leakage from the output signal into the forward mixer. The pattern suggest the attached cable acted like an antenna The fourth picture is the change of the amplitude of the forward mixer. (green line) with a through from CH0 to CH1. The bridge (red line) stops working above 1.5GHz as the characteristic pattern of the cable disappears, possibly because of insufficient measurement SNR Till now I have not been able to get valid phase signal from the bridge above 1.5GHz, only amplitude with at least 20% noise. Comparing the absolute levels of the signals suggests there is about 10dB headroom for increasing the thru signal and about 20dB for increasing the reflection signal. In particular the latter might have a big impact in the performance of the bridge at higher frequencies. I hope this information is not too detailed but writing it down helps me to understand it much better. |
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Re: errors of "error" models
#53 : Upgrade : The [LeastVNA]
- after: #48 : ann : update 3 of [LeastVNA] is withdrawn 15 October 2019 /g/nanovna-users/message/4945 - Hello, Allow us, please, to inform you that we just finished our research regarding the [LeastVNA] description of [AnyVNA], which from now on exists in our small objective world as the one given by this 39 characters long expression: Thank you very much indeed all of you who constructively commented on this crucial matter ! Sincerely, gin&pez@arg 53# |
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Re: Owen Duffy on improvised test fixtures
#test-jig
I have made a test jig for my VNA based on a ZIF sockettest jigs added to Wiki Application Notes /g/nanovna-users/wiki/Application-Notes |
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Supply noise at higher harmonics
#internals
When using the nanoVNA at frequencies above 300MHz it switches to harmonics mode
First attached picture shows the harmonics till 1600MHz of the SI5351 output when set at 100MHz. The 9th harmonic is at 900MHz only 34dB below the fundamental at 100MHz. To validate the performance of the SA612 I soldered two wires to output of the REF mixer and observed the output using a balanced USB audio input Second picture shows the 8k audio FFT when the nanoVNA is set to 1MHz. About 100dB SNR at this small audio BW. The nanoVNA uses less points (48) in its calculations and has therefore substantial less SNR The third picture shows the output when set to 2GHz. The SNR is reduced to something between 20 and 30dB This 80dB signal reduction is much larger as the reduction of power in the harmonics but can probably be attributed to the mixing loss in the SA612 as it it operated way out of spec (max 500MHz) The fourth picture shows the roughly 50dB SNR you get when you operate the nanoVNA at 2GHz from a clean 5V supply. A very welcome improvement making S21 measurements possible. A quick calculation based on the schematic suggests the REF mixer has the highest signal levels while the TRAN mixer is 10dB lower and REFL is 20dB lower If I have enough courage I may change the attenuators for the REFL and TRAN mixer to get more balanced power levels. |
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Re: errors of "error" models
#52 : Update : The compact SLO formula for [AnyVNA]
- after /g/nanovna-users/message/5081 - 17 October 2019 /g/nanovna-users/message/5075 - 17 October 2019 by Gary O'Neil - @Gary O'Neil: Dear Gary, Thank you very much for your most valuable comments ! Allow us, please, to ask you to give us enough time to prepare our replies. Meanwhile, take into account, please, that you already motivated us to attempt to write a minimal set of statements, valid more-or-less in ANY computer language having NO internal type of COMPLEX variables and only a REAL one, regarding : #42 : The compact SLO formula for [AnyVNA] - 12 October 2019 /g/nanovna-users/message/4747 in order to be ready for embedding them in ANY related program by the interested reader of- and/or contributor to- this thread of messages. However, during the transferring of that formula to statements, and after we found and corrected an existing typo in it, we finally succeeded a further compactification of it, and thus we updated it, as follows: that is in a super-mini form most appropriate for this particular work : Thank you - Please, stay tuned Best regards, gin&pez@arg 52# |
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Re: Owen Duffy on improvised test fixtures
#test-jig
Hi
Perhaps the caption should have been "nanovna-saver ¨C a premature look". I mean it is of version 0.1.0. I took a different approach than writing a blog entry, or webpage, about it, namely to engage in the evaluation, and report my findings and suggestions to Rune. So from a kind of "aaaahhhh, no thanks" to "OK, interesting - let's see what this can become." Indeed I had my head scratching moments too. The very first one was the NanoVNA and -Saver and the indiscriminate use of CH#, Port# and S## (My NanoVNA measures S00, and S10 instead of S11 and S21 etc.). I did a lot of wrong calibrations. Yes, the return loss, S11 (S00), reflection coefficient are not three different names for the same thing. But I am sure we will get there. With the very best of intentions Bo |
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Re: Test fixtures
#test-jig
I have one of the $9.00 eBay bridges, and a noise source.Enhancing nanoVNA by an eBay 3GHz RF bridge is interesting. Before getting nanoVNA, I considered using SDR and noise source with eBay clone Warren Allgyer seemingly reported comparable results /g/nanovna-users/message/2484 using 3GHz bridge with nanoVNA vs nanoVNA alone, which resistive bridge was analyzed by alan victor /g/nanovna-users/message/1252 QRP RX described using nanoVNA to measure 3GHz bridge directivity /g/nanovna-users/message/2880 Erik, PD0EK uses 3GHz bridge in his 35MHz - 3GHz breadboard VNA /g/nanovna-users/message/2054 /g/nanovna-users/message/3422 |
gin&pez@arg
Oristo
Bo, OZ2M