How do amplitude modulation and frequency modulation differ?

Answer 1

Amplitude modulation is where a constant carrier is modulated by the signal, so that the envelope of the carrier represents the signal.

Frequency modulation is where a constant carrier is modulated by the signal, so that the frequency of the carrier represents the signal.

Phase modulation is where a constant carrier is modulated by the signal, so that the phase angle of the carrier represents the carrier.

Answer 2

For a sound wave coming from a Flute for example, frequency modulation (FM) would be changing the "note" you play at a fixed volume, whereas amplitude modulation (AM) would be changing the "volume" of the fixed note you play.

I use sound as an easily understood vehicle, however this applies to a wave in any medium.

Information can be encoded on a wave by changing the "notes" (in a continuous fashion, like in a Trombone. i.e. FM) or changing the "volume" (i.e. AM). There are other ways to encode information in a wave too, but those are a distraction for the purposes of this AM/FM question.

To put a small bit of math on it:

W(t) = A * sin ( F*t + P )

W is the wave amplitude, t is time. FM varies F, AM varies A, P (phase) is an arbitrary constant for the purposes of this question, however it too can be modulated. You can graph W(t) on a computer and see what changing A and F does, as t goes from 0 to some time T in small increments.

There are many tradeoffs in choosing how to modify a base wave (or waves) to transmit information that can be faithfully decoded at a receiver over a communications channel (for example free space, or a telephone line, or a fiber optic cable etc)

Answer 3

Frequency modulation waves have higher frequencies and more energy than amplitude modulation waves. They pass through the ionosphere instead of being reflected back to Earth. Thus, frequency modulation waves do not travel as far as amplitude modulation waves. So, if you go on a long car trip with an FM radio station tuned in, you may quickly lose reception of the station. But frequency modulation waves are usually received clearly and produce better sound quality than amplitude modulation waves.

Answer 4

Phase Modulation :http://en.wikipedia.org/wiki/Phase_modulation

Amplitude Modulation :http://en.wikipedia.org/wiki/Amplitude_modulation

cheers!

Answer 5

because recieving hardwere is complex pm is used in digital synthesizers

Answer 6

in amplitude modulation amplitude of the carrier wave is changed with respect to the intensity of the modulating signal where as frequency and phase of the modulating signal is kept constant

Answer 7

modulation:- the characteristic varying in Carrier signal,according to the message signal

if amplitude is changing then amplitude modulation