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Is there any algorithmic way to determine if the mixed frequency offset in an SSB SDR demodulator is wrong (too high or low), other than listening for funny sounding voices? (perhaps by checking to see if voiced vowel spectral overtones fall in a harmonic series or seem inharmonic?)

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    $\begingroup$ There are methods using pattern recognition which attempt to detect the offset. It's been a while since I've read anything about that, so I'll have to try to look it up. $\endgroup$ – AndrejaKo Feb 5 '17 at 20:56
  • $\begingroup$ Yeah, that was a long time ago. The OP is really referring to balancing the DBM in SSB receivers. Back in the home-brew days that could be a chore. Now they come in ICs which have been balanced at the factory. And yes, you are basically right about the method, except that we would switch back and forth between USB and LSB and tune the thing so they sounded roughly equivalent. No formal algorithm necessary except whatever software runs in our heads.. $\endgroup$ – SDsolar Feb 20 '17 at 21:36
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According to this 2010 Icom patent, there may indeed already be a way to do this.

This method uses no pilot tone, carrier, etc. A brief excerpt:

In contrast with the above prior art, the invention requires no modifications to the transmitter and so a receiver equipped with this invention can be used with any SSB transmitter in use today. It can also correct for much larger tuning errors. As discussed in detail below, this invention analyzes the properties of the transmitted human voice, independent of language and retunes the receiver to the actual transmitted signal frequency with a high degree of accuracy. This can be done faster than a trained operator can retune the radio.

Apparently, this has never been put into production, which casts some doubt about the claims made there.

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    $\begingroup$ I'm not a lawyer, but it seems to me that this patent effectively blocks any other company from implementing such a feature in their receivers. If Elecraft, FlexRadio, Yaesu, Kenwood, etc. did, couldn't Icom sue them? $\endgroup$ – Mike Waters Feb 6 '17 at 22:13
  • $\begingroup$ I suppose we'll have to see if they can find a way to do it in a slightly different way, like RCA did to Philo Farnsworth, or wait until 2027 to see them do it. $\endgroup$ – SDsolar Aug 17 '17 at 21:57
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I remember seeing articles about it in the past, but nothing about it in years.

The most promising was to insert subaudible tones on all transmitters so the receivers can get a solid lock, like the military used to do.

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    $\begingroup$ This is what for example aviation SELCAL does. $\endgroup$ – AndrejaKo Feb 6 '17 at 1:33
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    $\begingroup$ SSB with a subaudible tone sounds like AM. $\endgroup$ – Phil Frost - W8II Feb 6 '17 at 2:33
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    $\begingroup$ @PhilFrost-W8II I see differences: using only one sideband, and potentially: using less bandwidth because the tone is closer to the audio band than an AM carrier, and using less power by using the minimum power needed for the receiver to lock on it (which if you do it to AM is called overmodulation). $\endgroup$ – Kevin Reid AG6YO Feb 6 '17 at 2:43
  • $\begingroup$ @AG6YO DE AL7EM - You hit the nail on the head. Upvote. Having a carrier would be "out of band" in terms of audio, and would divert a lot of the transmitter power output to the carrier. $\endgroup$ – SDsolar Feb 6 '17 at 5:42
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    $\begingroup$ @KevinReidAG6YO There are AM schemes that reduce the carrier power, and transmit only one sideband, retaining various degrees of compatibility with simple AM receivers. See <en.wikipedia.org/wiki/…>. $\endgroup$ – Phil Frost - W8II Feb 6 '17 at 13:11

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