Patent GB-270749-A (GB)
Title: Improvements in wireless signalling
IPC: H03C3/18
Filed: 1927-05-07
Abstract: 270,749. Soc. Francaise Radio-Electrique. May 10, 1926, [Convention date]. Magnetic modulating systems and apparatus; secret and selective systems ; atmospherics, eliminating or limiting; multiplex signalling. - In order to economize power, modulation is effected by controlling the phase of the carrier currents (a) in such a way that amplitude variations result, or (b) in such a way that phase variations alone transfer the signal, and the resulting high-frequency currents are afterwards passed through thermionic amplifiers. According to the first method, the output from a high-frequency source 1, Fig. 1 (which may be a small-powered generator of the rotating-field type) is transferred to two circuits 3 - - 6, 3<1> - - 6<1>, arranged so that the respective currents fed through power amplifiers 9, 9<1> to the aerial 12 are normally say 150 degrees out of phase. Microphone current is then fed from a transformer 7 into a circuit containing iron-cored inductances 6, 6<1>, fed with direct current from a battery 8. The effect of the signal currents is to increase the saturation of one coil, say 6, and to diminish that of coil 6<1>, thus setting up a periodical phase-variation between the currents in the circuits 3 - - 6 and 3'- - - 6', which combine vectorially in the aerial and give rise to corresponding amplitude variations. An alternative system according to the first method is shown in Fig. 2, where high-frequency voltages in quadrature with those in the windings 3, 3<1> of the rotating-field high-frequency source 1 are fed into a modulator 6 from a third output coil 4. The modulated output from 6 is fed back into the two first circuits by transformers 8, 8<1> and the resultant phases are passed through the amplifiers 9, 9' and combine vectorially to give amplitude variations in the aerial as before. Modulation by means of phase variations occurring at a frequency equal to that of the signalling currents, but without giving rise to amplitude changes, may be effected according to the second method by arranging the battery 8, Fig. 1, in series instead of in parallel as shown, so that the windings 6, 6<1> are saturated or desaturated simultaneously. In this case the relative phase of the voltages applied to the amplifiers 9, 9<1> does not vary, but only the phase of these voltages with respect to the primary currents passing through the windings 2<1>, 3<1>. The same effect can be secured by reversing one of the windings 2, 3 or 2<1>, 3<1> in the arrangement shown in Fig. 2. Fig. 5 shows a receiver in which the output from a frequency-changing amplifier 2 is passed, without detection, through high and low pass band filters 3, 4. The latter are inserted to separate the upper and lower side bands before detection, otherwise they would cancel out owing to the fact that they are in phase opposition. Each band filter 3, 4 is combined with a detector (not shown) separately, and the resultant output is fed to a low-frequency amplifier 6, the sense of the windings 5 being such that the out of phase telephone currents are added together. Phase-modulated carrier waves are not detected by a receiver of ordinary type, so that the system affords secrecy. Also. since the two detectors at the receiving end are in opposition, atmospheric disturbances are largely balanced out. Finally, several musical frequencies may be fed simultaneously into the signalling circuits 7, Figs. 1 and 2, and subsequently filtered out at the receiving end, so that the system may be used in this way for multiplex telegraphy.