CHARACTERISTICS OF RADIO RECEIVERS Sensitivity Selectivity Fidelity

Sensitivity Ability to amplify weak signals. Minimum RF signal level that can be detected at the input to the receiver and still produce a usable demodulated information signal. Broadcast receivers/ radio receivers should have reasonably high sensitivity so that it may have good response to the desired signal But should not have excessively high sensitivity otherwise it will pick up all undesired noise signals. It is function of receiver gain and measures in decibels.

Sensitivity of a receiver is expressed in microvolts of the received signal. Typical sensitivity for commercial broadcast-band AM receiver is 50 μV. Sensitivity of the receiver depends on : Noise power present at the input to the receiver Receiver noise figure Bandwidth improvement factor of the receiver The best way to improve the sensitivity is to reduce the noise level.

Selectivity Selectivity of radio receiver is its ability to differentiate desired signal from unwanted signals.

Selectivity is obtained by using tuned circuits, which are tuned to desired frequency. The quality factor of these LC circuits determines the selectivity. It is given by, Q=XL/R For better selectivity ‘Q’ should be high.

Fidelity Fidelity is defined as – a measure of the ability of a communication system to produce an exact replica of the original source information at the output of the receiver. Any variations in the demodulated signal that are not in the original information signal is considered as distortion. Radio receiver should have high fidelity or accuracy. Example- In an A.M. broadcast the maximum audio frequency is 5 KHz hence receiver with good fidelity must produce entire frequency up to 5KHz.