GB625486A - Improvements in or relating to radio and like relay systems - Google Patents

Abstract

625,486. Radio signalling. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. April 8, 1946, No. 10789. Convention date, April 9, 1945. [Class 40 (v)] At a radio relay station handling signals consisting of a frequency-modulated subcarrier frequency modulated on to the main carrier, additional channels are modulated on to the signal by extracting the modulated subcarrier and beating it with an oscillator modulated by the additional channels. The in- ' coming 3000 mc/s. signal at the relay station shown in Fig. 1 are frequency-modulated by a 1 mc/s. sub-carrier which in turn is frequencymodulated to the extent of Œ200 kc/s. by a group of 6 speech channels formed by modulating each channel on to separate local oscillators and selecting the lower sidebands. This signal which is received on aerial 2 is amplified at an intermediate frequency and detected to produce the modulated sub-carrier which is passed via lead 14 to mixer 28. Here it is combined with an 11 mc/s. signal from beat oscillator 26 to produce a modulated 12 mc/s. signal which is passed to mixer 36 where it is combined with a 13 mc/s. signal from beat oscillator 50 to reproduce the 1 mc/s. modulated sub-carrier. This is finally amplified at 38 and modulated on to a 3010 mc/s. carrier for retransmission. The additional modulation is effected by modulating the 11 mc/s. beat oscillator 26 by means of reactor valve 68 which is controlled through pre-emphasis network PEN by the local channel assembling unit 72. In a similar manner further modulation may be added by means of reactor valve 56 connected to the second beat oscillator 50. Unit 22 is provided to monitor some of the channels of the received signal. In an alternative arrangement (Fig. 2, not shown), the two beat oscillators are modulated in push-pull by one signal to produce twice the deviation. Specification 625,488 is referred to.