Experimental radio bearer equipment for carrier telephone systems

Two types of frequency-modulated radio bearer circuits are described, one operating in the frequency range of 420 to 470 Mc/s, and the other in the frequency range 860 to 960 Mc/s. Both systems are crystal controlled with a frequency deviation of ±180 kc/s and each capable of carrying 12 to 17 telephone circuits. The description includes a radio repeater operating on the heterodyne principle which permits long distances to be traversed with a minimum of accumulated noise and distortion. The performance of both systems meets C.C.I.F. transmission specifications when used with the appropriate carrier equipment. Various aspects of supervisory and order-wire facilities, together with alarm and automatic change-over equipment are discussed. A typical installation, operating in the 420¿470 Mc/s band and consisting of a transmitter, repeater and receiver, is described and its performance over a 100-mile circuit is given.