The KiwiSDR 2 online store is open for orders! Please visit kiwisdr.nz
NBFM audio degraded in v1.590? [fixed in v1.592]
I just tried listening to NBFM from a local 70cm repeater after updating FW and the demodulated FM on a v1.590 Kiwi seems quite distorted on voice peaks and the LF rolloff doesn't seem to work properly any longer. The waterfall display looks reasonable and demodulating on my IC7300 at the same time sounds fine. AM and USB demodulation seem fine too.
I don't remember what version I was last using for NBFM but I think it has been within a few weeks.
The signal from the rx converter is quite strong but I have no ADC OVs indicated. Has something changed or have I forgotten something obvious since I last listened?
Glenn
Comments
Yes, something did change. Let me look at this..
Should be fixed in v1.592
Thanks John,
Yes, it seems to have returned to the previous performance. Audio distortion seems low although I may still be hearing something happening at higher deviations (not sure) and I can still hear background sub-audio, 100 Hz in the case of a local repeater, to some degree even with the compensation engaged.
I'm not sure that the compensation isn't reasonable as is though. It looks like it is common to set the subaudible deviation to around 1 kHz peak but user audio is all over the place and I think ill-controlled. Maybe a higher corner frequency and more-poles in the HPF might be better but I'm not really sure of that and it is not really a very objectionable compromise as it is.
Thanks for sorting this out. I'll report again if I think there is something else going on at higher deviations/modulation indexes.
Glenn n6gn
Some systems (even commercial an military ones) have the sub audible tones set at far too high a level.
Ideally they should be at around 10 to 15% of the peak system deviation.
1kHz in a 12.kHz channelised system using typically +/- 2.5KHz peak deviation is far too high.
Regards,
Martin