frequency lock system - one up on P L L

5-18 — elektor may 1980 frequency lock system one up on PLL One of the basic requirements of any radio receiver is a stable front-end (or tuning heart), with the ability to tune a station in, and hold it without drifting. Automatic Frequency Control (AFC) was one of the first methods found to solve this problem, but it ran into trouble when trying to tune in a weak station, adjacent to a strong one. Then PLL same along. The PLL (Phase Locked Loop), while solving the AFC pitfall, was tricky to design and complicated. There is now a system that promises to be the future standard of tuners. Even though the superhetrodyne re- ceiver is an invention dating from the earliest days of radio, the principle behind it nevertheless remains valid. Almost every radio operates on an oscillator which is mixed with the aerial signal to produce an IF signal. Early tuners had terrible drifting prob- lems. In modern units however, the oscillator gets a little electronic help. This is necessary beca...