Q.Define selectivity.

A radio receiver picks up the modulated wave from its antenna and turns it back into sound. Its main functions are to: (1) intercept the incoming modulated signal; (2) select the wanted station from the many carriers present; (3) amplify that selected carrier; (4) detect it, separating the message from the carrier; (5) amplify the recovered audio; and (6) convert the audio into sound through a loudspeaker.

The quality of a receiver is judged by five characteristics, each a standard II PUC Electronics definition:

• Sensitivity — the ability to respond to a weak signal, measured as the minimum input (in microvolts) needed for a specified output. A typical AM broadcast receiver has a sensitivity of about 50 μV. It depends on the overall gain and the signal-to-noise ratio.
• Selectivity — the ability to pick out the wanted station and reject others. It is set by the bandwidth of the tuned circuit, which depends on its quality factor $Q = f_r/BW$: a higher Q gives a narrower bandwidth and sharper selectivity.
• Fidelity — the ability to reproduce faithfully at the output the signal present at the input. It depends on the bandwidth of the audio amplifier. …