Thread: AM, FM, PM Modulation Question

Hi,

Concerning RF.

It's my understanding that the amplitude of the modulating signal is always used to modulate the carrier signal regardless if it’s AM, FM or PM

Is this true ?

If so, Can someone help me to understand whats different between the modulating signal for all three.

Or correct me if I’m wrong.

Thanks,
-Areal

U CAN SEE THE BOOK "principles of communication systems" by TAUB & SCHILILNG

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

AM - Amplitude modulation: http://en.wikipedia.org/wiki/Amplitude_modulation

FM - Frequency modulation: http://en.wikipedia.org/wiki/Frequency_modulation

PM - Phase modulation: http://en.wikipedia.org/wiki/Phase_modulation

u should read the "ANALOG AND DIGITAL COMMUNICATION BY B.P LATHI"CH#4,5

That is incorrect.
FM uses the frequency to transmit information so your Amp can be completely
saturated and still change freq. Phase mod is closely related to FM.

You might be thinking of QAM. Where you do have Phase and Amplitude
being used to send data.

Cheers

no, for example FM is a constant envelope modulation, the amplitude doesn't contain any information

Well you're right. The modulating signal is the same in all cases. The difference is how the carrier is modulated by the information signal

Hy
i think u r confused!!!
simple way to understand :
modulating signal=input signal (signal to be sent)
for modulating signal,
use appropriate modulation technique to send data over any channel.
for more
study
carlson
frenzel
lathi (good for novice)
Regards

LATHI book will help you more to understand the diff between them

Hi,
Your statement is correct, that is, Whatever be the type of modulation, it is the amplitude of the modulating signal that is used to modulate the carrier.
Regards,
Laktronics

hi,

as laktronics said, your statement is correct..

since we need to transmit the message signal we use it to modulate the carrier, hence the name 'modulating signal'... to transmit the message signal we need to know its amplitude at each time instant at the receiver. so the amplitude of the message (modulating) signal will be used to change:

1. the amplitude of the carrier in case of amplitude modulation,
2. the frequency of the carrier in case of frequency modulation,
3. the phase of the carrier in case of phase modulation...

these figures explain the difference. the book of lathi will help you to understand the concept better.






best regards

Hi Friend,

Refer "Principles of Electronic Communication Systems" By Kennedy



Regards,
Avinash.S.

if you have a signal a high frequency one, the you can send information of a slow frequency signal on within it,
if you vary the amplitude of the hf signal you have am, if you slightly modify the frequneyc i se less than 5% you have fm, and if you change its phase with respecto to a reference signal you have pm , see lathi for a mathematical covering, a lite one.

MODULATING SIGNAL (VOICE) + CARIER SIGNAL MODULATED SIGANAL

if we use varying amplitude of modulating signal to modulate its AM

if we use varying FREQUENCY of modulating signal to modulate its FM

PCM IS OTHER THING .IT USED PULSES TO GET IDEA OF MODUALTING SIGNAL AND THAT DATA WILL TRANSMIT BASICALLY.THIS ROUGH IDEA TO YOU

It is completely wrong. because only in AM amplitude will used for modulation. For FM and PM signals amplitude has a constant value and frequency and phase changes.