Why do we require to provide a dc shift with a message signal before modulating the carrier in AM?
Answer:
The envelope of the AM signal must never go through zero, or severe distortion would result.
Because the AM signal is produced simply by multiplying the carrier by the message signal, the message signal has to have enough DC added to make its negative values positive, so that the resulting signal never goes through zero.
You don't. I'm not sure where you got that idea from. Worked in RF for 30 years and never did that.
I agree with "rrabbit". In double sideband modulation, a DC bias is applied to avoid the message signal going below zero.
More reading on
http://www.mee.tcd.ie/~ledoyle/teaching/...
I agree with Gene. An AM modulator requires no DC shift.
Unless if you have a DSB generator, and are trying to unbalance the mixer to create a carrier, then modulate it? That would give you AM.
Kind of the long way around though.
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