There was a time when all radio receivers contained at least one, now with the advent of the varicap diode and the frequency synthesiser the traditional tuning capacitor is a rare breed.

A varicap tuned MOSFET RF amplifier followed, and then a local oscillator. Finally it became a fully-functional FM radio, with probably far better performance than most commercial radios.

A four-to-one capacitance range is not problematic. In fact, a typical varactor diode (sometimes called a "varicap diode") can vary from 60 picofarads (pf) at zero-bias down to 15 pf at 20 volts (V).

With careful manufacturing, however, the capacitance range can be increased to ten-to-one. Varactor diodes, which are sometimes referred to as varicap diodes, are used in electronic tuning systems to ...