Frequency Stabilization of Radio Transmitters

The importance of maintaining constant the frequency of radio transmitters has been universally recognized and the investigation of methods of frequency stabilization was left as a pending question after the first meeting of the C.C.I.R. The quartz-control system with thermostatic temperature control of the quartz crystal should be utilized when the highest precision (of the order of 0.001 per cent) is required in the constancy of the transmitted frequency. However, the system necessitates a complicated and expensive installation and at the same time the frequency of transmitters is not so flexible. When the highest precision is not of primary importance the following methods devised by the writers may be applied with the advantages of simplicity and lower cost of installation. These methods, fully described in the present paper, may readily be applied to a master oscillator so as to give a frequency stability of the order of 0.01 per cent. (a) Constant-frequency oscillator. In an ordinary self-oscillator, the effect of the variation in supply voltages may be minimized by simple means. Two methods have been developed for the purpose: 1. Resistance-stabilized oscillator. 2. Phase-compensated oscillator. (b) Quartz-stabilized oscillator. A quartz crystal is introduced in the grid circuit of an oscillator in such a manner that it is very loosely coupled to the oscillator but still retains its stabilizing function. Power output of the oscillator can be obtained up to 100 watts or more and thus the number of stages of amplifiers to be used in a transmitter can be reduced.