I have wondered if it was possible to have a feature that auto tuned SSB. I can often get close to the correct position visually so if I can eyeball that could you write code to have a better guess?
Hi Peter,
You ask an interesting thing. With a mode like CW, the radio tunes to a specified pitch. Since the CW signal is very narrow, it’s easy to just offset from the peak and tune to pitch. For modes like AM and FM, with defined (and stationary, frequency-wise) carriers, automatic tuning can also be done (such as the 9700 does with AFC enabled).
For SSB though, this is quite tough. The best strategy is to set the tuning step to 1 KHz, and make sure the “When tuning, set lower digits to zero” option is selected under Settings. This will make sure that wherever you double-click in the waterfall ends in “000” which is typically the correct tuned frequency these days with our fancy low-PPM reference radios. You can then use the + and - keys, or even shift-+ and shift-- to fine-tune.
Since SSB lacks a carrier and we don’t know the pitch of anyone’s voice a priori (and a voice is much more complex than a single pitch anyway), it’s not very likely to become a feature even when we move into doing our own DSP.
I’m open to ideas though if anyone has done something like this!
–E
de W6EL
This would be possible with good S/N signals as most SSB sets do not have infinite carrier suppression.
One would shift down for LSB or up for USB a 100hz then with a steep bandpass and auto correlation dig out the carrier record its actual freq then move back by exactly this amount.
Professional ssb services insert a sub carrier for this to take place (this is much like the 19kHz pilot for FM)
usually in the sub audible range.
The above technique would work down to S/N ratios of 10dB and above as the autocorrelation would be able to dig down to about 40dB below the noise floor
Lots of DSP code to write --the modern pc is fast enough to do this for audio
That makes sense. I have never seen a ham radio that does this. It would be pretty neat.
on the other hand. most rigs are quite spot on. You see/hear most of the times two different ssb signals
- ex. 14.302.0
- ex. 14.207.5
which means that if you step 500 Hz, you are most of the time within a few Hz in ssb. Obvioulsy older analog rigs are different. My experience is like the examples above but I must say that I generally listen to ragchew talks or contests on HF.
When it comes to 2m and above you see quite some older rigs and/or rigs that are a few hundred Hz off.
That is some amazing stuff, right there!
There are algorithms for auto-tuning SSB. At least one has been around since 1970, in a thesis from the Naval Postgraduate School. In general they involve comparing the frequencies you get from a (possibly mistuned) SSB radio with what you get from an AM detector on the same signal. The AM detector will give beat notes between harmonics of the voice signal, which can be used to determine the pitch of the speaker’s vocal cords. This is useful because the SSB signal is usually filtered to exclude those low frequencies. This information can then be used to tune the SSB signal.
I don’t know of anyone who has actually implemented any of these algorithms, though.
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