Question

Buffer amplifier is used at the transmitting end to
(a) Feed carrier frequency to Master oscillator
(b) to amplify carrier frequency
(c) to mix modulating signal with carrier frequency
(d) to isolate master oscillator from other stages of transmitter

Answer 1

Hint: A buffer amplifier is used in an AM transmitter. The AM transmitter consists of the oscillator stage, buffer and multiplier stages, driver stage and a modulator stage. The master oscillator feeds the buffer amplifier. The oscillator stage is followed by the buffer stage.

Complete answer:
 A buffer amplifier provides electrical impedance transformation from one circuit to the other circuit, to prevent the signal source from being affected by whatever currents that the load may be produced with.
A master oscillator in the AM transmitter generates a stable sub harmonic carrier frequency. A crystal oscillator used to generate this stable sub-harmonic oscillation. Later the frequency is raised to the desired value by a harmonic generator. The carrier frequency should be very stable. Any change in this frequency will cause interference with other transmitting stations. As a result, the receiver will accept programs from more than one transmitter.
The tuned amplifier which provides high input impedance at the master oscillator frequency is a buffer amplifier. It helps to prevent any variation in the load current. Due to its high input impedance at the operating frequency of the master oscillator, the variation does not affect the master oscillator. Thus, the buffer amplifier isolates the master oscillator from the other stages, so that the loading effect may not change in the frequency of the master oscillator.

Therefore, the answer is option D.

Note:
Frequency modulation and amplitude modulation are used to transmit data using the method of modifying the carrier signal. The main difference between both modulations is: in amplitude modulation, amplitude of the modulating wave is modulated, whereas frequency modulation the frequency of the carrier wave is modified.