• The selectivity of a receiver is its ability to reject unwanted signals. It is expressed as curve as shown.

• It shows that the receiver offers a minimum rejection at 950 kHz i.e. at the tuned frequency, but the rejection increases as the input signal frequency deviates on both the sides of 950 kHz.

• The selectivity of a super heterodyne receiver is determined by the frequency response characteristics of the IF amplifier. The responses of the mixer and RF amplifier stages also play a small but significant role.

• The selectivity decides the adjacent channel rejection of a receiver.

• Higher the selectivity better is the adjacent channel rejection and less is the adjacent channel interference.

Attenuation DB