On Mon, Sep 23, 2019 at 03:06 AM, david mugridge wrote:
The nanovna has a very strong 1KHz component - probably a result of the
1KHz codec frame-rate.
I opened the nanoVNA and connected the line in of a good USB audio device to the reference SA612. But as I did not dare to do two connections the unbalanced signal had a lot of noise. And there were 1kHz peaks independent from the selected output frequency, possibly coming from the PC itself as connecting the audio input to the ground of the nanoVNA gave the same noise.
Looking with a scope showed a very clean triangular 5kHz signal, although with some jitter that might explain some of the disturbances we see.
As disconnecting the USB resets the nanoVNA U was not able to measure with disconnected USB as I do not know how to stop the sweep (e.g.the writing to the SI5351) from the UI
