Disadvantages of Amplitude Modulation

In amplitude modulation, the sidebands contain the signal. The power in the sidebands is the only useful power. The power carrier by the side bands is only 33.3% even when there is 100% modulation. If modulation is 50%, then power carried by the sidebands is 11.1%. Clearly, the useful power is small. So, the amplitude modulation has low efficiency.

Sub Topics

Noisy Reception
Small Operating Range
Reproduction is not of High Fidelity
Applications

Noisy Reception

Different types of atmospheric and other electrical disturbance are reproduced in amplitude modulation receivers. This makes the reception noisy.

Small Operating Range

Due to small useful power the messages cannot be transmitted over large distance. So, the transmitter based on amplitude modulation has small range.

Reproduction is not of High Fidelity

For high fidelity reception, the audio frequencies from 20Hz to 20000Hz must be reproduced. This requires a bandwidth + 20000Hz i.e., 40000Hz. (Note that both the sidebands must be reproduced). The bandwidth actually assigned for AM transmission is 20000Hz. This is done to keep the interference from adjacent broadcasting stations to a minimum. Thus, the highest modulating frequency is 10000Hz. This is not sufficient to reproduce music properly. Thus, the reproduction is not of high fidelity.

Applications

Amplitude modulation is utilized in many services such as television, standard broadcasting, aids to navigation, telemetering, radar, facsimile etc. Although the message content may vary widely for these, the mechanism of combining the message and the message carrier at the sending terminal is basically the same.