what's all this ssb stuff?

[Martin Czech]

Sorry if my previous mail was confusiong to some people.

So:

Single Sideband Modulation ->SSB 
Four quadrant multiplication with a sine
yields two sidebands, upper and lower (USB, LSB).
SSB manages to get rid of one of them.
You can try it with filters (hopeless for audio
but good enough for radio).

Or the phase method by Weaver:

sin(w*t)*sin(v*t)           = 0.5*(-cos((w+v)*t)   +cos(w-v)*t) = 0.5*(-cos((w+v)*t)+cos(w-v)*t)
sin(w*t+PI/2)*sin(v*t+PI/2) = 0.5*(-cos((w+v)*t+PI)+cos(w-v)*t) = 0.5*(+cos((w+v)*t)+cos(w-v)*t)

w,v signal/carrier frequency

See? Add or subtract and one sideband is lost.
The problem is to get PI/2 phaseshift.

That's why polyphase ladders or "Hutchins" active circuit are used,
to get a phase shift of PI/2 for the signal.
And quadrature oscillators to get a sin(v*t) and sin(v*t-PI/2)=cos(v*t)
modulator.

The audio effect of ssb in contrast to "ringmodulation" is that
the missing sideband is not heard , when your signal moved uo, you don't
hear the mirror sideband move down to zero... and up again.

For low modulation frequency (1 Hz) you get phasing when mixed with original signal.
Yoiu get beating there with "ringmodulation".

Finally ssb can fm any signal...
m.c.