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I catch some strange bug in the latest firmware. I tried to get better resolution around 26.996500 MHz to see crystal resonance. Span 10 kHz works ok. But when I trying to setup span=9 kHz or 5 kHz or any value below 10 kHz I just got strange measurement fail with saw waveform on the screen. See screenshots.

Steps to reproduce:
1) Set center frequency 26.9965 MHz
2) Set span 10 kHz and make sure all is ok
3) Set span 5 kHz and make sure there is a bug.

Any idea why it happens?

update: I tested previous firmware version nanoVNA_900_ch_20190802 and this bug is missing. So, this bug was added in the latest firmware nanoVNA_900_ch_20190920.dfu

update 2: it doesn't matter what frequency is selected for the center frequency. This bug happens when you set span smaller than 10 kHz

I've seen at least one firmware version where the minimum attainable step
size was 100Hz. I don't exactly know why, but your findings fit my
observations as well.

--
Rune

Just tested, with previous firmware version (nanoVNA_900_ch_20190802.dfu) it works ok with 5 kHz span. I tried even 10 Hz span and it works ok.

But the new firmware version (nanoVNA_900_ch_20190920.dfu) cannot works with a span smaller than 10 kHz.

The same issue happens when you trying to setup start frequency 10000 k and stop frequency 10005 k.

So, this issue was added in the latest firmware.

Hi,
I have tested a lot of firmware version, and never one of them has allowed a frequency step below 100Hz.
Are you sure of your previous test ?
To have a firmware allowing a more precise frequency granularity will be really usefull. As exemple to analyse CW filters.
Regards,
David, F4HTQ.

Just tested previous firmware it works stable with 1 kHz span. Yes, it has wrong measurement with span below 100 Hz. But the new firmware is unstable below 10 kHz, this is much more worse...

Hi,

That's for you :

@edy555 edy555 released this 2 hours ago
in-device TDR support (contributed by @cho45)
add scan command for multisegment scan excess 101 points
fixed invalid sweep at the narrow span (<5kHz)
fixed failures caused by a race condition between USB and measuring loop
find device automatically in python script




Regards,
David F4HTQ

David

The scan command implemented by edy555 can scan max 101 points.
I tried to convince him otherwise but failed.

Erik PD0EK

Erik,

The latest edy555 release says the scan command supports more than 101 points:

0.2.0-20190928
edy555 released this 4 hours ago
in-device TDR support (contributed by @cho45)
add scan command for multisegment scan excess 101 points
fixed invalid sweep at the narrow span (<5kHz)
fixed failures caused by a race condition between USB and measuring loop
find device automatically in python script

Herb

Indeed. That is what I hoped but when I inspected his code I saw he did not copy my code but is using an array to store the frequencies. The frequency array has only 101 items

Thanks Erik,
I admit I was puzzled because its obvious that the nanoVNA has only limited memory storage and can only accumulate so many data points. I was guessing by Hugen's use of "segments" that he meant the scan command would allow collecting more data in additional segments of 101 points each.

Herb

My implementation did not have a limit on the points scanned but of course edy555 is free to do different
Maybe hugen has a better solutiom

It appears that the latest firmares still do not support a freq step less than 100 Hz. Are there any plans to support a smaller step size? 1 Hz would be great. 10 Hz would be good. Use cases would be narrow cw filters and crystal parameter measurements.