Question

The subsystems in an FM receiver are
A. Mixer
B. RF amplifier
C. Limiter
D. IF amplifier
Choose the correct sequence of subsystems in an FM receiver from the options given below:

• A. A, B, C, D
• B. A, C, B, D
• C. B, A, D, C
• D. C, B, D, A

Hint:

The basic signal path in a superheterodyne receiver is always: RF Amp \(\to\) Mixer/LO \(\to\) IF Amp \(\to\) Demodulator. FM receivers have the additional special stage of a Limiter right before the demodulator to remove AM noise.

Answer 1

The Correct Option is C

Step 1: Recall the block diagram of a standard superheterodyne FM receiver. The received signal from the antenna is processed in a specific order to extract the original message.

RF Amplifier (B): The first stage is a tuned Radio Frequency amplifier. Its purpose is to amplify the very weak signal from the antenna and provide some initial selectivity to reject signals far from the desired frequency (like the image frequency).
Mixer (A): The amplified RF signal is then fed to a mixer, along with the signal from a local oscillator (LO). The mixer performs frequency conversion, down-converting the RF signal to a fixed, lower Intermediate Frequency (IF).
IF Amplifier (D): The signal at the IF is then passed through several stages of IF amplification. Most of the receiver's gain and selectivity are provided in this section.
Limiter (C): Before demodulation, the IF signal in an FM receiver is passed through a limiter. The limiter is a circuit that removes any amplitude variations from the signal. Since the information in FM is purely in the frequency variations, these amplitude variations are considered noise and must be removed for a high-quality output.
(After the limiter comes the FM demodulator/discriminator, followed by an audio amplifier.)

Step 2: Form the correct sequence. Based on the standard architecture, the correct sequence of the given blocks is RF amplifier \(\to\) Mixer \(\to\) IF amplifier \(\to\) Limiter. This corresponds to the sequence B, A, D, C.