GB301436A - Improvements in wireless communication - Google Patents

Abstract

301,436. Robinson, J. May 27, 1927. Secret and selective signalling systems.- Signals are transmitted by using two or more sets of carrier waves or modulations differing in frequency or in some other characteristic, and the radiation is shifted from one carrier to another at a frequency less than the carrier frequencies but greater than the signal frequency; and reception is effected by separate receivers having their detectors connected in opposition to a circuit tuned to the shift frequency. Figs. 1 and 2 show the transmitting and receiving circuits respectively. Two carrier - wave generators V1, V2 are coupled through amplifiers V3, V4 to transmitting aerials A1, A2. These aerials are rendered active alternately by coupling a valve V5, oscillating at the shift frequency, to the grid circuits of the valves V1, V2, causing them to oscillate in turn. The receiver employs separate aerials a1, a2 tuned to the respective waves and connected to detector valve v1, v2 which are coupled in push-pull fashion to a circuit L5, C5 tuned to the shift frequency. The distinctive radiation from the desired transmitter builds up a resonant oscillation in the circuit L5, C5. Other signals or disturbances affecting the receiving circuits a1, a2 simultaneously will not affect the circuit L5, C5. The signal may be sent as a modulation of the frequency or the amplitude of either or both the carrier waves, or of the shift frequency generated by the valve V5. Instead of using separate carrier waves as the alternate channels, separate modulations of a carrier wave or of two carrier waves may be employed. Moreover, one or both channels may comprise two carriers used simultaneously. According to the Provisional Specifications, one of the carrier waves may be suppressed, the signal being sent by intermittent trains of the other carrier. Two receiving circuits are used as in Fig. 2, only one of which is tuned to the carrier wave, and the circuit L5, C5 is tuned to the frequency of intermittence. Specification 278,479 is referred to.