Patent GB-934013-A (GB)
Title: Electronic coding device for radio or telephone links
IPC: C01G43/01
Filed: 1961-10-25
Abstract: 934,013. Radio signalling. COMPAGNIE INDUSTRIELLE DES TELEPHONES. Oct. 25, 1961 [Oct. 28, 1960], No. 38194/61. Class 40 (5). Relates to a single sideband suppressed carrier communication system in which the carrier frequency is cyclically switched to different values to provide secrecy. The lowfrequency signal to be transmitted is applied at 1, Fig. 1, to a modulator 2 supplied with a frequency of 250 kc/s. obtained by frequency division at 5 of 1000 kc/s. provided by a generator 4. Synchronizing pulses to be transmitted are supplied to the modulator at 1<SP>1</SP>. The output of the modulator is supplied via a filter 6 selecting the upper sideband (250.3 to 253 kc/s.) to a second modulator 7 which is supplied at 8 with a frequency having a cyclic variation in the range 900 to 899.1 kc/s. The frequency at 8 is obtained from a mixer 9 receiving 1000 kc/s. input from the generator 4 and one of ten coding frequencies 100, 100.1 ... 100.9 kc/s. selected by an electronic switch 13 from a group 12 of crystal oscillators. The output of the modulator 7, containing one of the frequencies 1150, 1149.9 ... 1149.1 kc/s. is applied to a third modulator 15 which also receives an input F from a device 17 which starting from a frequency of 1000 kc/s. gives a signal which may be adjusted kilocycle by kilocycle. The modulator 15 provides outputs with carrier frequencies of F-1150, F-1149.9 . . . F-149.1 kc/s. The electronic switch 13 is shown in Fig. 2, the device also being used for switching the carrier frequencies for the receiver. With the switch K at position E (transmit) an oscillator 21 via a frequency divider 22 supplies short pulses of duration not longer than 100 milliseconds and spaced by 1.01 seconds to control a bi-stable flip-flop 19. These pulses also are passed via terminal 1<SP>1</SP> to control the modulator 2. On reception of a pulse the flip-flop 19 operates and opens a gate 24 to allow a 1 kc/s. signal from a generator 25 to pass via a divider 26 providing pulses of duration 0.01 seconds and period of recurrence 0.1 seconds to a counter 27 comprising four flip-flops. In order to obtain the desired decimal counter the ninth pulse 1001 causes the counter immediately to substitute 1111 which normally would represent 15, and the tenth pulse then restores the counter to zero, the divider 26 to zero, and the flip-flop 19 to normal. The eight outputs of the flip-flops 27 are supplied to a decoding matrix 28 having sixteen outputs of which ten are used, each of the ten positions of the counter 27 producing a corresponding condition of the matrix output. These outputs are multiplied on the contacts of ten manual switches X 1  . . . X 10  whose moving contacts are respectively connected to gates P 1  . . . P 10  associated with oscillators S 1  . . . S 10  which supply the ten different frequencies to the input 11 of mixer 9. Thus the order of succession of the different frequencies on input 11 of the mixer 9 is determined by the positions of the moving contacts of the switches X 1  &c. With the switch K in the receive position R, synchronizing pulses are selected by a circuit Y from the incoming signals and the circuit operates as for transmission. Transistor crystal-controlled oscillator circuits S 1  &c. and transistor gate circuits P1 &c. are described, Fig. 3 (not shown), and the diode matrix 28 is described, Fig. 4 (not shown). Specification 884,921 is referred to.