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-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.
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