GB566785A - Improvements in or relating to radio communication systems - Google Patents

Abstract

566,785. Wireless signalling. STANDARD TELEPHONES & CABLES, Ltd., and ULLRICH, E. H. April 11, 1941, No. 4850. [Class 40 (v)] [Also in Group XXXVI] A signal is isolated from the echoes due to reflection in the upper atmosphere by transmitting the signal on two or more wavelengths, and at the receiver changing the received waves to the same wavelength by heterodyning, and then combining the resulting waves in suitable phase relation. Either the direct signal or the echoes may be made available for reception, or they may be used in combination if time delay networks are interposed. The system may be used in locating objects by reflection. The receiving-circuit shown comprises filters 2, 3 passing respectively the two wavelengths #1, #2. The former passes directly to a transformer 12, and the latter is heterodyned by a source 6 through a phase-adjuster 5 to produce a wavelength #1 which is selected by a filter 7 and passed to a transformer 13. Each transformer has two secondary coils which are crossconnected to produce an adding effect in one detector 8 and a subtracting effect in the other detector 10. The Specification shows that by suitable choice of the frequency difference in relation to the time lag of the echo signal behind the direct signal, these signals are separately available at the output of the detectors 8, 10. As shown, they are combined in the telephones 11, the direct signal being suitably delayed by a network 9. The Specification discusses the case when more than two wavelengths are employed, and indicates that frequency-modulated transmissions may be used. For purposes of adjustment pulse signals from the transmitter may be received on a cathode-ray indicator to show the time-lag between the direct signal and the echoes, and thus enable optimum frequencies to be found. Specification 296,827, [Class 40 (v)], is referred to.