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# Computer Networks | Analog-to-Analog Conversion

In this article you'll understand the basic concept of Analog-to-analog modulation. First let us understand what is an Analog signal? An analog signal is any continuous signal for which the time-varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It can have an infinite number of values in a range.

Analog signal

ANALOG-TO-ANALOG CONVERSION:

Analog-to-analog conversion, or modulation, is the representation of analog information by an analog signal.

Now a question arises that why there is a need for analog-to analog modulation as it is already analog?

Modulation is needed if the medium is bandpass (it is a device that passes frequencies within a certain range and rejects frequencies outside that range) in nature or if only a bandpass channel is available to us.

• Example - A radio. The government assigns a narrow bandwidth to each radio station.

• The analog signal produced by each station is a low-pass signal, all in the same range.

• To be able to listen to different stations, the low-pass signals need to be shifted, each to a different range.

1. AMPLITUDE MODULATION : In Amplitude Modulation transmission of the carrier signal is modulated so that its amplitude varies with the changing amplitude of the modulating signal.

• The frequency and phase remains the same, only the amplitude changes.

2. FREQUENCY MODULATION (FM) : In FM transmission the frequency of the carrier signal is modulated to follow the changing voltage level of the modulating signal.

• The amplitude & the phase remains constant, but as the amplitude of the information signal changes the frequency of the carrier signal changes accordingly.

3. PHASE MODULATION (PM) : In PM transmission the phase of the carrier signal is modulated to follow the changing voltage level of the modulating signal.

• The amplitude & frequency of the carrier signal remains constant.

Happy Learning!

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