COMPARISON OF AM AND FM

NO. FM AM

1. Amplitude of FM wave is

constant and independent of

modulation index

Amplitude of AM wave is

varying and dependent of

modulation index

2. So transmitted power remains

constant and independent of

modulation index

So transmitted power

dependent on modulation

index

3. No. of sidebands having

significant amplitude depends

on modulation index

No. of sidebands will be

constant and 2 sidebands

4. FM receivers are immune to

noise

AM receivers are not immune

to noise

5. Bandwidth=2(fm+Δf) Bandwidth=2fm

6. Bandwidth is large. Hence

wide channel is required.

Bandwidth is less than FM.

7. Space wave is used for

propagation. So radius of

transmission is limited to

LOS.

Ground and sky wave

propagation used. Large area

coverage

8. FM transmission and

reception equipments are

complex.

AM transmission and

reception equipments are less

complex.

9. Information is carried in the

frequency variation of the

carrier.

Information is carried in the

amplitude variation of the

carrier.

10. Eg:-Radio and TV

broadcasting, police and

Radio and TV broadcasting

wireless, point to point

communications

No.

Parameter PAM PWM PPM

1 Waveform

2 Variation parameter

Amplitude Width Position

3 Bandwidth required

Less

Bandwidth of transmission channel depends on width of pulse

High

depends on risetime of pulse

High

depends on width of pulse

4 Noise immunity

Low High High

5 Transmitted power

Varies with amplitude of pulse

Varies with width of pulse

Remains constant

6 Need for synchronization pulse

No No Yes

7 System Complex Simple to implement Simple to implement8 Complexity

of generation and detection

Less More More

9 Similar to AM modulation

FM modulation PM modulation