Difference between FM and AM Signal

Nov 30 -0001

Distinguish, differentiate, compare and explain what is the difference between FM and AM Signal in Radio Broadcasting, Transmission and Reception. Comparison and Differences.

In an FM signal, the frequency of the signal is changed by the modulation (baseband) signal while its amplitude remains the same. In an AM signal, we now know that it is the amplitude (or the envelope) of the signal that is changed by the modulation signal.

Amplitude modulation, AM, is one of the most straightforward ways of modulating a radio signal or carrier. It can be achieved in a number of ways, but the simplest uses a single diode rectifier circuit. It is simple to implement and can be demodulated using a circuit consisting of very few components. AM receivers are very cheap as no specialised components are needed.

Frequency modulation (FM) is the standard technique for high-fidelity communications as is evident in the received signals of the FM band (88-108 MHz) vs. the AM band (450-1650 KHz). The main reason for the improved fidelity is that FM detectors, when properly designed, are not sensitive to random amplitude variations which are the dominant part of electrical noise (heard as static on the AM radio). Frequency modulation is not only used in commercial radio broadcasts, but also in police and hospital communications, emergency channels, TV sound, wireless (cellular) telephone systems, and radio amateur bands above 30 MHz.

Difference between FM and AM Signal

S.No.	Frequency Modulated - FM Signal	Amplitude Modulated AM Signal
1	The amplitude of carrier remains constant with modulation.	The amplitude of carrier changes with modulation.
2	Carrier frequency changes with modulation.	Carrier frequency remains constant with modulation.
3	The carrier frequency changes according to the strength of the modulating signal.	The carrier amplitude changes according to the strength of the modulating signal.
4	The value of modulation index (mf) in FM can be more than 1.	The value of modulation factor (m) cannot be more than 1 for distortion less AM signal.