What is the name of the circuit that develops AFC voltage in RADAR receivers?

The circuit that develops Automatic Frequency Control (AFC) voltage in RADAR receivers is known as a discriminator. A discriminator is specifically designed to convert frequency variations of the input signal into a corresponding voltage output. In the context of RADAR receivers, this voltage is used to adjust the local oscillator frequency so that it remains synchronized with the frequency of the incoming signal, ensuring optimal performance and reducing signal distortion.

Discriminators operate by comparing the frequency of the incoming RADAR signal with a reference frequency, effectively identifying deviations that indicate whether the local oscillator needs to be adjusted. This adjustment is crucial for maintaining the sensitivity and accuracy of the RADAR system, as it helps to prevent misinterpretation of the signals.

In contrast, peak detectors are typically used to capture and hold the peak value of a varying signal, which is not directly related to frequency control. Crystal mixers serve to combine signals or facilitate downconversion but do not generate AFC voltage. Second detectors are generally employed in a different context within the receiver architecture, often focused on signal demodulation or detection. Hence, the discriminator stands out as the essential circuit for developing AFC voltage in RADAR receivers.