Crystal control at 1000 megacycles for aerial navigation

A schematic of a post-war system of distance-measuring equipment employing an airborne interrogator and a ground transponder, is given. Equipment operating in the 960-1 215 Mc/s band giving 51 two-way clean channels, each not more than 2.5 Mc/s wide is described. An indirect transmitter frequency control system is used, in which a pulsed oscillator is employed for transmission, its frequency being continuously compared with the output of the low-power crystal oscillator and multiplier system, and automatic correction applied to keep its frequency within prescribed limits.