Electrical – AM Modulator with BJT 2N3904

Your perfectly single-sideband suppressed-carrier modulated sinusoid certainly has a phase which can be measured. However, what you cannot tell is what the contributions of that measured phase from the audio input and the RF oscillator were.

There is another form of single-sideband modulation, in which not only one sideband but also the carrier component is transmitted. This provides a reference which can be used to synchronize the receive LO to the transmit one - normally done to insure exact tuning, but it would also give you the ability to recover the original audio phase.

It is also quite possible, especially with modern DSP gear, to transmit two separate audio channels, one on each side band. This is commonly called independent sideband modulation (ISB).

Many spread spectrum implementations are DSP based and capable of receiving multiple channels at once - GPS being a good example.

I don't understand I in your formula.

Normally (traditionally) AM is: -

y(t) = [A + M cos(ωm t + φ)] . sin(ωc t)

where

• y(t) is the final modulated signal
• M is the amplitude of the modulating cosine (or sine to answer your question)
• A is the amplitude of the carrier sine (or cosine to reinforce the answer!!)
• φ is the phase displacement of the modulating sinewave but is irrelevant all but mathematically
• ωm and ωc are the frequencies of modulation and carrier.

Maybe I just don't recognize your formula but the answer is, like Jim Dearden implies swap them up or use the same because carrier and modulator are not going to be the same frequency when dealing with AM.