GB353906A - Improvements in or relating to multi-channel or multiplex high frequency signalling systems - Google Patents

Abstract

353,906. Multiplex wireless signalling. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, MATHIEU, G. A., 3, Mayfield Gardens, Shirehall Park, and PUCKLE, O. S., 10, Lawrie Park Crescent, Sydenham, all in London. April 29, 1930, No. 13200. [Class 40 (v).] A multiplex transmitting system comprises a master-frequency source, means for producing a plurality of dissimilar frequencies from said source, means for separately modulating one of them by each of the others, and means for modulating the resultant frequencies by signals. In one modification the master-frequency source TF comprises a valve-maintained tuning-fork 1, and the master frequency is fed to a multi-vibrator circuit MV, the output frequencies of which are amplified at A passed through a high-pass filter F, further amplified at A1, and then fed to coupling coils C . . C, in series or series-parallel. The coil C is coupled to a selector S which passes one of the frequencies to a second multi-vibrator MV2, one of the frequencies from which is selected by S8 and fed to coupling coils C<1>1 . . C<1>7. The coils C1 . . C7 are coupled to selectors S1 . . S7 which pass seven different frequencies to the pairs of modulating valves V1, V<1>1 .. V7, V<1>7 to which the coils C<1>1 .. C<1>7 are also coupled. Keying of these modulators may be effected by keys K1 . . K7, arranged to alter the grid bias on the modulating valves. Band-pass filters F1 . . F7 which pass only the upper (or lower) sidebands follow the modulators and feed amplifiers A<1>1 . . A<1>7 whose output is combined in a composite unit CU, the mixed frequencies passing to a submodulator SM, modulator M associated with the drive D, side-band suppressor CF, power amplifier PA and radiating aerial A. A similar reversed arrangement may be used at the receiver. The radio carrier frequency may also be obtained from the tuning fork, and an extra frequency may be drawn from the system to modulate one of the channels for tuning-in and lining-up, and if desired two or three channels may be used together for telephony transmission. In a slight modification, Fig. 1a (not shown), an intermediate valve is placed between the source TF and multi-vibrator MV, being fed through a potentiometer and condenser, both of which may be varied to vary the amount of control exercised by the tuning fork. In a further modification, Fig. 2 (not shown), all the frequencies are produced by a series of frequency doublers and triplers. Specification 305,703, [Class 40 (v), Wireless signalling &c.], is referred to.