Re: AM Modulation


abhishekemitt...@xxxxxxxxxxxxxx wrote:
when v see the o/p of a AM Modulated signal in frequency domain ,why
there r three frequencies ? in spite of modulating signal is made of
single frequency?

You see the carrier frequency, the carrierfreqiuency plus the
modulation frequency, and the carrier frequency minus the modulation
frequency.

When you modulate a carrier, you are essentially multiplying two sine
waves toegther

sine A. sin B = 0.5 .(cos (A-B) - cos(A+B))

This implies that you shouldn't see the carrier frequency at all, but
few modulators are perfect multipliers.

Single side band modulation schemes use 90-degree pahse shifters to
generate cosine A and cosine B so that one can form the second product

cosine A. cosine B = 0.5.(cos (A-B) + cos (A+B)

which cn then be summed with the first to suppress the sum frequency
(or - with very little more ingenuity) the difference frequency,

Electronics is really just a branch of trigometry .

--
Bill Sloman, Nijmegen

.

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