Abstract :
Varactor tuners have become increasingly popular over the last few years. Mechanical tuners may soon be a thing of the past as new, lower cost, more versatile tuning systems are developed. Several methods of interfacing the customer to the varactor tuner have already enjoyed market acceptance or have been published. All of these tuning systems fall into one of two major categories. Closed loop, or "frequency" systems are precise, crystal controlled, generally inflexible, and usually very expensive. They require local oscillator outputs from the tuners and gigahertz counters or prescalers. Open loop, or "voltage" systems are flexible, low cost, easily adapted to low-speed large scale integrated circuit technology, can be completely static in operation and are sufficiently precise for the task.
