Abstract :
In radio link equipment, frequency control of the transmitter by the use of a resonant cavity has been used since the very early days of the radio link technology and many different AFC arrangements have been designed. One simple design uses a cylindrical cavity where both the two orthogonal TE/sub 111/ modes are exited. One mode is tuned slightly lower than the other, and diode detectors sample the power from the two modes but with opposite polarity, so the combined voltage from the two detectors appears as a discriminator curve.
