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How does an FM radio set work?
The FM receiver is the whole unit which takes the modulated signal as input and outputs the original audio signal. Radio amateurs are the initial radio receivers. They had got drawbacks such as poor sensitivity and selectivity.
Selectivity is the selection of a particular signal while rejecting the others. Sensitivity is the capacity of detecting RF signal and demodulating it, while at the lowest power level. Both Selectivity and Sensitivity should be high for an FM receiver. To overcome these drawbacks of the ordinary receiver, the superheterodyne receiver was invented. This FM receiver consists of 5 main stages.
RF Tuner Section
The modulated signal received by the antenna is first given to the tuner circuit through a transformer. The tuner circuit is nothing but an LC circuit which is also called as resonant or tank circuit. It selects the frequency, desired by the radio receiver. It also tunes the local oscillator and the RF filter at the same time.
RF Mixer
The signal from the tuner output is given to the RF-IF converter, which acts as a mixer. It has a local oscillator, which produces a constant frequency. The mixing process is done here, having the received signal as one input and the local oscillator frequency as the other input. The resultant output is a mixture of two frequencies produced by the mixer, which is called the Intermediate Frequency (IF)
The production of IF helps in the demodulation of any station signal having any carrier frequency. Hence, all signals are translated to a fixed carrier frequency for adequate selectivity.
IF Filter
Intermediate frequency filter is a bandpass filter, which passes the desired frequency. It eliminates any unwanted higher frequency components present in it and noise. IF filter helps in improving Signal to Noise Ratio (SNR)
Demodulator
The received modulated signal is now demodulated with the same process used at the transmitter side. The frequency discrimination is generally used for FM detection.
Audio Amplifier
This is the power amplifier stage which is used to amplify the detected audio signal. The processed signal is given strength to be effective. This signal is given to the loudspeaker to get the original sound signal.
This superheterodyne receiver is well used because of its advantages like better SNR, sensitivity, and selectivity.
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