ssb demodulation with phase shift

[Zardosht]

Hi
I would appreciate if anybody can help me about ssb demodulation that the received signal have phase shift,this need synchronization ,transmitter and receiver.I have some problem about reconstruct signal.
best

 

[WimRFP]

I don't know exactly what you mean, but as long as the local oscillator (beat frequency oscillator) has the correct frequency for good demodulation, the phase of the (suppressed) carrier with respect to the beat frequency oscillator doesn't matter.

So very slowly changing phase between the original SSB carrier and your Local Oscillator does not detoriate the audio, as long as the frequency difference is sufficiently small. You have to make sure that you only multiply one side band with the local oscillator

If you have also some of the other sideband energy present, then best performance you get when the LO signal is in phase with the original carrier that created the SSB signal. A synchronous AM detector (using both side bands) requires zero phase difference.

 

[Zardosht]

thank you for reply.
What about the situation that phase is changing fast?
If i don't inform about carrier(fc) in receiver how can recover it? How can i find which sideband is received?

 

[WimRFP]

Hello

You may know that "delta omega" = d(phi)/dt, phi in radians.

If the phase changes fast, you have (too) much difference in frequency between the local oscillator and the original carrier of the SSB signal. This causes the demodulated audio to shift too much in frequency, hence reducing the audio quality.

When you would do the demodulation on the transmitters frequency (that is direct conversion zero IF). If you increase the frequency of the LO and the audio frequency spectrum reduces, you are demodulating the upper side band. When increasing the LO frequency and the audio spectrum increases, you have the lower sideband.

You know upper side band frequencies are above the carrier. So when you increase the LO somewhat, the frequency difference between the LO and the upper side band spectrum reduces, hence the average frequency of the audio reduces.