A Variable FrequencyOscillator (VFO) is a simple, free-running oscillator that has limited frequency adjustment capabilities. It is used primarily in amateur radio
and its frequency is determined by the LC components. A VFO has few requirements for frequency accuracy and frequency drift. Both are unavoidable in VFOs and are strongly affected by temperature and voltage changes. Reduction of drift
is possible with circuitry measures. For this purpose, various manufacturers work with so-called half-frequency oscillators, which can be built with less drift and double their frequency. The frequency of VFOs is adjusted with variable capacitors or trim capac itors, which are adjustable capacitors. The accuracy is 0.2 % to 1 %, which corresponds to a frequency deviation of 200 kHz to 1 MHz at 100 MHz. For this reason, VFOs are not used in radio and television equipment.