Question

Main function of the RF amplifiers in a superheterodyne receiver is to?
A. Amplify signal
B. Reject unwanted signal
C. discriminate against image frequency signal and IF signal
D. all of the above

Answer 1

RF amplifiers viz radio frequency amplifiers are used to amplify the low input radio frequency signals. We need to amplify because the RF signals are usually at low voltages. Because of low voltage they are prone to external disturbances. Boosting the signals usually means increasing the voltage and decreasing the current and vice versa.

Complete step by step answer:
-A superheterodyne receiver works by changing the RF frequency into a lower IF frequency and then this signal is amplified and demodulated to get the desired signal which may be in the form of a video signal. It also works as a receiver by using frequency mixing to change a received signal to a constant intermediate frequency signal.
-The signal is sent after being amplified with the help of a transmitter and at the receiving end, an antenna is used to collect the radio signal. The RF amplifier in superheterodyne provides selectivity by rejecting the unwanted signals. It also helps to discriminate against image frequency signal and IF signal.

Thus, it performs all the functions which are mentioned in the options and thus the correct option is (D).

Note: When a signal propagates through a medium many unwanted signals get mixed with it and thus at the receiving end we need to get rid of unwanted signals called noise. The key technique that is employed in the development of the superheterodyne receiver theory is that of mixing. This is not the analogue mixing used in audio additive mixers, but non-linear mixing or frequency multiplication that enables frequencies to be changed or translated.