Explain the following terms (i) De-emphasis (ii) Limiter (iii) Dynamic range (iv) FM discriminator (v) Sensitivity – NABTEB QUESTION

i. DE-EMPHASIS network is to reduce frequency modulation noise which enters the transmitted signal while route from the transmitter to the receiver as well as any such noise which may enter at the front end of the receiver.

ii. LIMITER CIRCUIT: Is used to remove amplitude variations from the FM intermediate frequency. It removes any AM noise which may enter at the front end of the receiver. Clipping by the limiter eliminates noise but does not affect the information content of the signal because the information is contained in the frequency variations not in the amplitude variation.

iii. DYNAMIC RANGE: Is the complete range of volume from no sound to maximum sound.

iv. F.M DISCRIMINATOR: for the detection of F.M waves the method usually employed involves the conversion of FM into AM and then application.

Demodulation of an FM waves involves:

– Conversion of frequency variations produced by modulation signal into corresponding
– Amplitude variations
– Rectification of modulating signal
– Elimination of RF component of the modulated wave
– For the FM detection we need a circuit in which magnitude of output voltage varies in accordance with the instantaneous frequency in the input voltage. Such circuits are called discriminators.

vi. SENSITIVITY: is a measure of the ability of a receiver to respond to weak signals.