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AFC provision for DSD digital voice modes.


David J Taylor
 

From my recent tests, it would seem that for receiving digital voice modes setting the frequency can be very critical when using the DSD plug-in.

For measuring, no problem - you would like to know of any such frequency errors.

However, for listening it occurs to me that some form of AFC would be helpful, but if that facility is present I may have missed it. I'm thinking of a very slow AGC, tens of seconds response time.

Have I missed the point, or would this be a helpful feature? Some of the dongles we use can have quite a drift....

73,
David GM8ARV
--
SatSignal Software - Quality software for you
Web: http://www.satsignal.eu
Email: david-taylor@...
Twitter: @gm8arv


Edouard Griffiths
 

Hi David,

we're talking about AFC here right? Because you mention "AGC" somewhere as well. So assuming it is AFC as in the title I don't really see a need for that. The issue is either Rx stability which is unlikely or Tx stability which is much more likely. I noticed that some transmitters even on pro networks are not very solid on their center frequency as I see the figure on the "magic eye" moving around the center. Usually this is not bad enough to cause significant disturbance on the decoding that has already the provision to accept some fluctuations. This has to be in the area of 100' Hz not kHz though.

Best regards,
Edouard.


David J Taylor
 

Hi David,

we're talking about AFC here right? Because you mention "AGC" somewhere as well. So assuming it is AFC as in the title I don't really see a need for that. The issue is either Rx stability which is unlikely or Tx stability which is much more likely. I noticed that some transmitters even on pro networks are not very solid on their center frequency as I see the figure on the "magic eye" moving around the center. Usually this is not bad enough to cause significant disturbance on the decoding that has already the provision to accept some fluctuations. This has to be in the area of 100' Hz not kHz though.

Best regards,
Edouard.
==============================

Yes, Edouard, AGC must have crept in unnoticed (and the spelling checker accepted it, of course!).

I find that begin 100 Hz off can create problems (at least in the DSD decoder) which spoil the listening enjoyment. Some dongle-based receivers can drift quite a bit, as they live in a much lower powered state compared to when they are running at full speed (just feel the case temperature), and other receivers (e.g. Pluto) have a real-crystal rather than the noisier TCXO, and are therefore much more likely to drift.

100 Hz drift at 432 MHz is better than 0.25 ppm, and I see that e.g. the Yaesu FT-2DE is specified at 2.5 ppm, so it would be really helpful if some sort of AFC could be optionally applied.

I don't know whether this is unique to the DSD decoder plug-in - certainly that where I would like to see the option rather than something in the base software. Thanks for considering it.

73,
David GM8ARV
--
SatSignal Software - Quality software for you
Web: http://www.satsignal.eu
Email: david-taylor@...
Twitter: @gm8arv


Edouard Griffiths
 

Hi David,

unfortunately this is a bigger task that one would think and I am not keen in giving this a high priority. This concerns anything FM based really. In comparison a RTL-SDR dongle with TCXO, SMA connector and aluminium case can be found at ~35 EUR: https://www.passion-radio.com/sdr-receivers/nesdr-smart-421.html I am using one of these to listen to NXDN channels and do not need to ever tweak the frequency.

Brgds, Edouard.  


David J Taylor
 

Hi David,

unfortunately this is a bigger task that one would think and I am not keen in giving this a high priority. This concerns anything FM based really. In comparison a RTL-SDR dongle with TCXO, SMA connector and aluminium case can be found at ~35 EUR: https://www.passion-radio.com/sdr-receivers/nesdr-smart-421.html I am using one of these to listen to NXDN channels and do not need to ever tweak the frequency.

Brgds, Edouard.
====================================

Edouard, I had been under the impression that the plug-ins were from third-parties, not something you had written yourself. No, it's not a top-priority item, but something which I feel would be useful given the very high sensitivity of DSD (at least the DMR mode) to small frequency errors.

Perhaps someone else might like the challenge of the work and submit it as an update? I'm afraid I know little of C/C++ and find it very difficult to read. Pascal/Delphi is no problem!

73,
David GM8ARV
--
SatSignal Software - Quality software for you
Web: http://www.satsignal.eu
Email: david-taylor@...
Twitter: @gm8arv