Patent GB-222216-A (GB)
Title: Improvements relating to secret intercommunication by oscillatory discharges
IPC: H04K1/00
Filed: 1923-04-03
Abstract: 222,216. Morrison, L. D. G., and Morrison, R. W. G. April 3, 1923. Secret signalling systems; undesired signals, eliminating.-Relates to a secret system such as is described in Specification 180,288 in which an irregular variation in wave-length, train frequency, or other characteristic is imparted to the transmitter, and means are provided to maintain the receiving circuit synchronously in tune with the imposed variations. According to the. present invention the imposed variations are smooth or continuous, as distinct from being "stepped," and provision is made for adjusting the phaserelation between the transmitter and receiver. The variable tuning is effected by means of condensers having irregularly-shaped plates, or having inter-leaving or " concertina " plates controlled by a specially-shaped cam, as shown in Fig. 11; or by asymmetric variometers or " concertina " inductance coils, Fig. 12; or coupled coils shielded to a variable degree as shown in Fig. 13, may be used for the same purpose. The last arrangement also ensures variation in the mutual coupling between the coils 66, 67 as the wave-length changes. The irregularities in wavelength may also be arranged so as to set up a confusing note in a series of unauthorized receivers tuned within the range of variations, in the manner shown in Fig. 5, where if five unauthorized receiving sets are tuned respectively from 6000 to 10000 meters so as to trap the signal in their combined output, such reception will be confused by a superposed frequency corresponding to eleven times the cycle-frequency of the imposd wave-length variation of the points numbered 1 to 11. An additional transmission on a different wave-length, corresponding to the curve WLC<2>, Fig. 6, may also be imparted by a separate oscillator 64, 65, Fig. 7, the tone signal frequency from the circuit 62, 63 being shown by the curve WLC<1>, Fig. 6. Authorized receiving sets are pro vided with a suitable wave-trap to reject this additional transmission. The irregular variometers 62, 65 may be geared to a common driving shaft An alternative circuit to Fig. 7 is shown in Fig 7<A>, the aerial 70 being energized from two dif ferently-tuned circuits 72, 72<A>, and 71, 71<A>, each of which mutually excludes the frequency gener ated by the other. In order to maintain the necessary synchrony between the tuned cricuits at the sending and receiving ends a control device such as a Siemens pendulum, or a stroboscope or a balance wheel, as shown in Fig. 3. may be employed. Tuning impulses sent out periodically from the transmitter energize an electromagnet 22 through a tuned receiving circuit 25 and a coherer 27, detector or amplifier. and so regulate the swing of a balance-wheel 20 carrying an adjustable soft iron armature-bit 21. The oscillating shaft 19, in turn, drives a shaft 1 which imparts the wavelength variation, say through the cams 57, 58 or 69<A> in Figs. 11, 12 and 13 respectively. The tuning inductances or condensers are in each case capable of independent manual adjustment for the purpose of bringing them into exact phase with the transmission, after the timing mechanism has been started up. When heterodyne reception is used, the local oscillating circuits are similarly maintained in synchrony so as to preserve a constant note frequency. Specification 149,283 is also referred to.