How is a varicap used in an AFC circuit?

How is a varicap used in an AFC circuit?

The AFC circuit senses the difference between the actual oscillator frequency and the frequency that is desired and produces a control voltage proportional to the difference. A varicap is used to keep the IF stable. The varicap application here produces an apparent reactance, which is included in the oscillator frequency control circuitry.

Which is the varactor diode in tunning circuit?

Varactor diode in tunning Circuit The figure below shows that D 1 and D 2 are the two Varactor diode. These diodes provide the variable resistance in the parallel resonance circuit. The V c is the DC voltage used for controlling the reverse voltage of the diode.

Why are AFC circuits used in radio receivers?

This variant of AFC circuits are used in radio receivers, fm transmitters, and frequency synthesizers to maintain frequency stability. It requires a relatively constant amplitude of the (received) input-signal. For pulse-radar sets this form isn’t practicable therefore.

Which is the varactor in the parallel resonance circuit?

The varactor diode is small in size and less in weight. The figure below shows that D 1 and D 2 are the two Varactor diode. These diodes provide the variable resistance in the parallel resonance circuit. The V c is the DC voltage used for controlling the reverse voltage of the diode.

How does an automatic frequency control system work?

Automatic frequency control circuits in a non-coherent or pseudo-coherent radar set uses two different but similar systems. The receivers frequency readjust the transmitter (Figure 3). Both systems retain a sample of the transmitted signal using a Directional Coupler fittet between the transmitter and the Duplexer.

Why does a microwave radar need Automatic Frequency Control?

Automatic Frequency Control The radar receiver requires a limited tuning range to compensate for transmitter and local oscillator frequency changes because of variations in temperature and loading. Microwave radar receivers usually use automatic frequency control (AFC) for this purpose.