Practical RF Handbook, 4th Edition

9

Oscillators

RF oscillators are used to produce the carrier wave which is required for a radio communications system. In the earliest days of ‘wireless communication’, spark transmitters were used; these produced bursts of incoherent RF energy containing a broad band of frequencies, although tuned circuits were soon introduced to narrow the band. However, valves and later transistors and FETs enable a single frequency oscillator to be produced. Typically, a tuned circuit is connected to the input of an amplifier, the output of which is coupled back into the tuned circuit. If it be arranged that at the resonant frequency of the tuned circuit, the gain from the input of the active device to its output, through the tuned circuit and back to its ...