Subelement C: Receiving Systems – 10 Key Topics – 10 Exam Questions – 4 Drawings— Topic 24: Automatic Frequency Control - AFC
Question 8-24C2
Element 8 (RADAR)A circuit used to develop AFC voltage in a RADAR receiver is called the:
Explanation
The discriminator is the correct answer because it is a circuit specifically designed to produce an output voltage that varies with the frequency of its input signal. In an Automatic Frequency Control (AFC) system, this voltage is used to detect any drift in the receiver's local oscillator frequency relative to the desired Intermediate Frequency (IF). If the IF drifts, the discriminator generates an error voltage (positive for too high, negative for too low, or zero for correct frequency) which is then fed back to adjust the local oscillator, maintaining precise tuning.
A peak detector (A) extracts the amplitude of a signal, not its frequency deviation. A crystal mixer (B) converts RF signals to IF signals by combining them with a local oscillator, but it doesn't generate control voltage for AFC. A second detector (C) is a general term for the stage that demodulates the IF signal to extract information, but the *specific* circuit developing the AFC voltage by sensing frequency shifts is the discriminator.
Related Questions
8-23C6 The video (second) detector in a pulse modulated RADAR system would most likely use a/an:8-24C1 The AFC system is used to:8-24C3 In the AFC system, the discriminator compares the frequencies of the:8-24C4 An AFC system keeps the receiver tuned to the transmitted signal by varying the frequency of the:8-24C5 A RADAR transmitter is operating on 3.0 GHz and the reflex klystron local oscillator, operating at 3.060 GHz, develops a 60 MHz IF. If the magnetron drifts higher in frequency, the AFC system must cause the klystron repeller plate to become: