Patent GB-610532-A (GB)
Title: Improvements in and relating to the synchronisation of radio transmitters
IPC: H04B7/155
Filed: 1945-10-12
Abstract: 610,532. Synchronizing radio transmitters. GENERAL ELECTRIC CO., Ltd., and STENNING, L. C. Oct. 12, 1945, No. 26654. [Class 40 (v)] Satellite broadcasting stations have their frequency locked with that of a master broadcasting station by radiating from the latter a linking wave which is picked up by the satellite station, multiplied or divided in frequency and heterodyned by a local source to produce a broadcasting frequency locked with that of the master station and independent of variations in frequency of the local source. In Fig. 1, the master station 10 generates a linking frequency at 11 which is radiated by the aerial 15, and is fed to a frequencydoubler 12 and amplifier 13, the output of the latter being broadcast by the aerial 14. At the satellite station 16, the linking-frequency is picked up by an aerial 17 and is heterodyned at 19 by a local source 20 to produce a lower I.F. which is selected, amplified and limited at 21, 22 and fed to a frequency-doubler 24. The output from 24 is mixed at 25 with a doubled version of the local oscillation from 20. The upper output frequency from 25 is selected and amplified at 27 and fed to the broadcasting aerial 28, thus radiating a frequency which is double that of the incoming wave at 17 and is independent of the local source and its frequency variations. In a modification, Fig. 3 (not shown), the linking frequency is higher than the broadcasting frequency, and at the satellite station is first reduced in two stages by multiples of a local oscillator frequency, is then divided by an integral factor, then multiplied by a smaller integral factor, and finally raised to the desired value by mixing with a selected multiple of the local frequency. The factors and multiples are so chosen that the broadcast frequency is independent of the local frequency. In a further modification, Fig. 2, two linking frequencies are radiated at the master station from a single aerial or from separate aerials 34, 35, both frequencies being derived as harmonics from crystal oscillators 30, 31. The two frequencies are mixed at 36 and their comparatively low difference frequency is multiplied at 37 and radiated from 38 as the broadcast frequency. At the satellite station the two link waves are picked up at aerial 39, and are mixed at 40 with a local oscillation 41, giving two comparatively low intermediate frequencies which are selectively amplified at 42, 43 and mixed at 44. The resulting difference frequency is the same as the difference between the incoming frequencies, and is multiplied up at 46 to the same degree as at the master station, thus yielding the same broadcast frequency from the satellite aerial 47 as is broadcast from the master aerial 38. The satellite station may have a second local oscillator of comparatively low frequency, which frequency is heterodyned with the I.F. before the latter is raised to the value desired for broadcasting. Frequency drift in this second local source causes a shift in the zones where reception is poor owing to interference between the radiations from two broadcast stations. The signal or programme may be phasemodulated on the broadcast wave emitted from the master station, and may be applied through a delay network to phase-modulate also the link frequency, the delay being such as to allow for the time taken in the path from master to satellite stations plus any delay at the satellite station. Specification 610,599, divided from the present Specification, is referred to.