Re: [soft_radio] Re: Autotuning SSB
Hello Dave, Once the fundamental pitch is identified, one needs to determine which of the present tones is the lowest transmitted. When I looked at the problem several years ago I failed on this first step. Surely many stations are easy and give a nice comb spectrum, but there are also signals that look irregular and noisy on the waterfall. The fundamental I could extract was uncertain and when I accumulated the extended comb spectra outside the passband there was no common origin. Surely most stations would give a good tune, but I was looking for something that would not fail. The spectrum of the voice will tend to be stronger in odd or even harmonics, so a further subdivision may be performed, and this can help delineate whether the lowest received pitch is 2nd, 3rd or 4th harmonic. When I look at real signals from HF bands this is not what I observe. I can not see any systematic behaviour in the overtone amplitudes. Finally, I have not observed speech processing to alter any of this. I think speech processing does not have to change the the comb-like nature of the SSB spectrum. Sometimes it does however. Only a few overtones survive and noise is filled in between. I did give it a try, but I was unable to find the carrier on the basis of power spectra in some cases. Stations that I could tune manually with no problem. My conclusion was that one should look at the phase also. I think I know how to do that now. The phase shift from transform to transform on each peak gives a better estimate of the frequency than a simple peak search. (Linrad uses that in its FM detector now.) Maybe I will return to this problem some day 73 Leif / SM5BSZ
RE: [soft_radio] Re: Autotuning SSB
Hi, Thanks for the feedback. Notch filters are very easy to implement, as are auto-notch filters. Simon Brown, HB9DRV http://sdr-radio.com -Original Message- From: soft_radio@yahoogroups.com [mailto:soft_ra...@yahoogroups.com] On Behalf Of Chris Muir And finally a good notch filter would be nice - manual ones seem the best. Ideally one that can be set to auto or tuned manually.
RE: [soft_radio] Re: Autotuning SSB
I agree - if we can hear the offset then it must be possible to determine it with a computer. Simon Brown, HB9DRV http://sdr-radio.com -Original Message- From: soft_radio@yahoogroups.com [mailto:soft_ra...@yahoogroups.com] On Behalf Of Leif Asbrink When heavy speech processing is used, a method based on power spectra fails completely. I can hear by ear so it must be possible to do it in the computer.
Re: [soft_radio] Re: Autotuning SSB
Chris wrote: Maybe your software could go a stage further i.e. measure the audio bandwidth and guess where the carrier should be? Hi, I don't know how existing SSB auto tuning systems work but I think it could be done by looking for fundamental tones F and their harmonics N*F in the speech spectrum and adjust the tuning until they line up properly. Just an idea... 73 Johan SM6LKM
RE: [soft_radio] Re: Autotuning SSB
I don't have the QEX article - I think there was a bit more to it than that. I don't have time at the moment but later this summer I will. Simon Brown, HB9DRV http://sdr-radio.com -Original Message- From: soft_radio@yahoogroups.com [mailto:soft_ra...@yahoogroups.com] On Behalf Of Johan H. Bodin I don't know how existing SSB auto tuning systems work but I think it could be done by looking for fundamental tones F and their harmonics N*F in the speech spectrum and adjust the tuning until they line up properly. Just an idea...
