AdvancedA-005-003-007

What is the reason for neutralizing the final amplifier stage of a transmitter?

D
Answer
Antennas and transmission lines
Type
A
To keep the carrier on frequency
B
To limit the modulation index
C
To cut off the final amplifier during standby periods
D
To eliminate parasitic oscillations

Answer Notes

The final amplifier stage of a transmitter operates at high power levels, making it particularly susceptible to self-oscillation caused by unintended feedback paths. These unwanted, self-generated signals are known as parasitic oscillations. Neutralizing the amplifier involves introducing a counteracting feedback path that cancels out the internal positive feedback from the tube or transistor's internal capacitance. By neutralizing this capacitance, the amplifier remains stable and does not generate these harmful parasitic oscillations. Distractors like keeping the carrier on frequency or limiting the modulation index are incorrect; those are functions of the master oscillator and audio processing stages, respectively, not the final RF amplifier.
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What does a neutralizing circuit do in an RF amplifier?
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Parasitic oscillations are usually generated due to: