Unequal sidebands on 40m, Valiant

[IN3IEX]

 

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Technically SSB AM is better than DSB AM. It requires half the spectrum and sounds the same after a traditional AM demodulator.
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AME (SSB with carrier) has around 35% distortion on a diode detector at 100% modulation.

Which stands to reason: it would be identical to a two-tone SSB test with equal tones. The envelope is not a sine wave; it is extremely pinched at the negative peak.

With AME, you also lose the diversity advantage of having two sidebands. That can be a very great advantage at times, as sync detector and PowerSDR users well know.

73,

Kevin, WB4AIO.

You are right. I made a mistake to recall the old mod to kwm2 without checking the mathematics.
Anyway by locally demodulating the rf output of an AM transmitter and using this signal to fm or to pm the vfo it is clearly possible to enhance one sideband or the other. This is an interesting starting point for reducing band occupation of an old tube transmitter. Still not very convinced but it looks interesting...

http://en.m.wikipedia.org/wiki/Beat_(acoustics)

[IN3IEX]

Here we have the pspice model of a phase modulated sine generator:
http://pspiceprograms.blogspot.it/2008/07/single-frequency-frequency-modulation.html
They say frequency modulation, but the model describes a phase modulation.

With PSPICE I simulated the AM modulation (100%) of a phase modulated carrier: with M=0.8 we have a good suppression of one sideband if the two modulating signals are 90 degrees out of phase.

As FM and PM are related by a derivative of the modulating signal:
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/RadCom/part12/page1.html

AM modulating an FM modulated signal may produce the approximate suppression of one sideband with the two modulating signals in phase or out of phase, without 90 degrees phasing filters.
With PM, with the 90 deg shifter, and with constant PM modulation index, the unwanted sideband suppression does not depend on the modulating frequency (that is good but the 90 deg audio filter is required).
Instead with FM, without the 90 deg audio shifter and with constant FM modulation index, the unwanted sideband suppression depends on the modulating frequency.

In addition we have residual sidebands from FMing the carrier.
In conclusion this system of sideband control is very rough, does not provide a clean spectrum, etc, but seems to work. It is not perfect indeed...
I have not studied in detail. No time to spend for it.

Therefore we may have a perfect AM (100%) envelope and one sideband reduction (or suppression), but we need more spectrum (FM related spectrum) to compensate for it. Interesting but useless, I suppose ;-)