GB685989A - Improvements in electric facsimile communication systems - Google Patents

Abstract

685,989. Wireless signalling. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). May 3, 1944, No. 8398/44. Class 40 (v). An electric facsimile communication system comprises means for transmitting a train of jamming pulses spaced apart at predetermined intervals, means for transmitting facsimile signals during certain selected ones only of the said intervals, and means for transmitting during one of said intervals a preparatory signal which conditions the receiver to respond to the facsimile signals. In the form shown in Figs. 1 and 2, a transmitting station 10 includes a generator 12 for producing jamming synchronizing pulses 38 which are radiated from a transmitter 16 on a first frequency, and a facsimile waveform generator 18 which is synchronized by generator 12 and which produces a facsimile waveform 40 which is radiated on a second frequency, in the gaps between jamming pulses, from a second transmitter 26. At the receiving station 24, a receiver 34 tuned to the pulse wavelength feeds a pulse detector 36 to obtain pulses used to synchronize the reproducer stage 32 of a receiver 26 tuned to the frequency of the facsimile signal. If desired. further confusion is caused by radiating random jamming pulses 42 between the synchronous jamming pulses 38 in the absence of a facsimile signal. To economise power, the reproducer 32 may be triggered into operation by a signal 41 which precedes the facsimile signal. In a modification, Fig. 4 (not shown), the jamming pulses are radiated on the same frequency as the facsimile signal. Fig. 6 shows a system in which a transmitter 64 and receiver 66 may operate in enemy territory under the supervision of a transmitter 62 in friendly territory. Transmitter 62 radiates synchronizing and random jamming pulses only. The synchronizing pulses are detected at 36 in station 64 and used to synchronize a facsimile waveform generator 18<SP>1</SP>, which radiates from transmitter 22. Receiver 66 is the same as 24 in Fig. 1 but receives its facsimile signal from station 64 and its synchronizing pulses from 62. This makes stations 64, 66 difficult to locate.