

27th August 2004, 15:40 #1
Member level 2
Diff bet FM and PM
what is the diff bet FM and PM?
i read from a book that freq diff of FM depends on freq of modulating signal but phase dev of PM is indep of freq of modulating signal.
pl give the respective formulas for freq & phase dev also.

27th August 2004, 15:40

28th August 2004, 10:31 #2
Advanced Member level 3
Re: Diff bet FM and PM
In FM, the information of a signal is encoded in its frequency. Similarly for PM, the information is encoded in its phase. Both modulation schemes use a carrier frequency as a reference.
A FM modulated signal with message signal x(t) has the form
A sin(2*pi*(fc+delta(f))*t) where delta(f) is the frequency deviation and is a function of x(t).
A PM modulated signal with message signal x(t) has the form
A sin(2*pi*fc*t + p) where p is the phase and is a function of x(t).
Digital signals usually use PM as its possbile to formulate orthogonal codes which provide error correction capabilities in a noisy transmission channel.

28th August 2004, 10:31

6th October 2005, 07:56 #3
Advanced Member level 2
Re: Diff bet FM and PM
HELLO checkmate
orthogonal codes which provide error correction capabilities in a noisy transmission channel
plz ur word orthogonal codes are less prone to noise.............
what about antipodal signals/codes...............

6th October 2005, 07:56

6th October 2005, 15:53 #4
Newbie level 5
Re: Diff bet FM and PM
hi frd
there is a basic difference betweem FM and PM
in FM, modulation index is inversely proportional to the modulating frequency but
in PM that is independent of the modulating frequency.
regards
puneet bansal