Q.With a block diagram explain the various stages of FM transmitter.

An FM transmitter processes the audio (with pre-emphasis) and uses it to vary the frequency of a carrier oscillator through a reactance/varactor modulator; frequency multipliers raise the carrier and deviation, and a Class-C power amplifier drives the antenna, with an AFC loop stabilising the centre frequency. …

[!TLDR]

An FM transmitter pre-emphasises the audio, uses it in a reactance modulator to frequency-modulate the oscillator, multiplies up the carrier and deviation, amplifies in Class C, and radiates - with AFC to keep the centre frequency stable.

The stages of an FM transmitter are:

1. Microphone: converts sound into the electrical audio (modulating) signal.
2. Audio (AF) amplifier: amplifies the weak microphone output to a suitable level.
3. Pre-emphasis network: a high-pass RC network that boosts the higher audio frequencies before modulation, so that after de-emphasis at the receiver the high-frequency signal-to-noise ratio is improved.
4. FM modulator: a reactance modulator (or varactor-diode modulator) connected to the master (carrier) oscillator. The pre-emphasised audio varies the effective reactance across the oscillator tank, so the oscillator frequency swings about the rest frequency in step with the message, generating the FM wave directly.
5. Frequency multipliers: raise the carrier frequency to the assigned broadcast value and, importantly, multiply the frequency deviation by the same factor to reach the required maximum deviation (75 kHz for broadcast FM).
6. RF power amplifier: a Class-C amplifier that raises the FM signal to the required transmit power (amplitude limiting is harmless because information is in the frequency, not the amplitude). …