Modulation It is the process by which characteristic

feature (such as frequency, amplitude, phase) of a carrier wave is modified in accordance with the intensity of the modulating/information signal.

Frequency modulation frequency of the high frequency carrier wave is modified

Amplitude modulation amplitude of the high frequency carrier wave is modified.

Amplitude Modulation (AM) If amplitude of modulating signal increases, then

amplitude of carrier signal also increases Note:

Amplitude of carrier wave changes Frequency of carrier wave remains unchanged Frequency of modulated wave is

same as frequency of carrier wave

Frequency Modulation (FM) If amplitude of modulating signal increases, then

frequency of carrier signal also increasesWhen the frequency of carrier wave is changed

in accordance with the intensity of signal, the process is called FM. Amplitude and phase of carrier signal remains constant

Advantages of Frequency modulation over Amplitude Modulation

1. Noise: FM offers a better immunity to unwanted random noise

and hence gives a higher Signal-to-Noise-Ratio (SNR). In case of AM, noise or unwanted electromagnetic

interference also gets modified along with the amplitude of the carrier wave.

2. Power efficiency: Since FM signals have a constant amplitude, therefore,

linear amplifiers are not required to increase the output power. Hence it gives a better transmitter efficiency.

In case of AM, in order to avoid distortion, about 2/3 power is concentrated in the carrier signal which effectively contains no information and hence it results in inefficient power usage.

Advantages of Frequency modulation over Amplitude Modulation3. Operating Range:

It is quite high in case of FM and messages can be transmitted over larger distances

Due to low efficiency in case of AM, transmitters used in AM have a small operating range.

4. Quality of reception: FM gives high fidelity reception. The AM wave is centered at the carrier frequency and

the useful information is carried in the sidebands at the signal frequency. Therefore, for a larger bandwidth is required for transmission of information. But, this is not available because of interference with nearby broadcasting stations. Hence, AM gives a low-fidelity reception.

Disadvantages of Frequency modulation over Amplitude Modulation

Bandwidth: The bandwidth of AM signal is twice the frequency of modulating signal. But incase of FM, the required bandwidth is much larger, and it puts a constraint on the frequency spectrum space required for transmission. Hence, an optimization criteria is followed to use FM over AM.

Circuit: A relatively complex circuit is required for making frequency modulators.