I'm just learining the basics of amplitude modulation and i had a question about sideband frequecies.... Why is there a need for sideband frequecies? if amplitude modulation is just changing the amplitude of a carrier with respect to the instantaneous amplitude of a modulating signal...why must the frequency of the carrier wave be affected at all? i dont understand the connection at all. why cant i just add or subtract to the voltage level of the carrier....why go for nonlinear mixing?
and my other question is in the armstrong indirect fm transmitter we use multipliers to increase the frequency by a factor of 72....then why not just use a bunch of multipliers on the original information signal in the transmitter stage to increase the frequecy to radio frequency...why go for modulation at all?