GB556079A - Improvements relating to multi-channel electrical communication systems - Google Patents

Abstract

556,079. Multiplex wireless signalling. STANDARD TELEPHONE & CABLES, Ltd., CHATTERJEA, P. K., and HOUGHTON, L. W. March 12, 1942, No. 3295. [Class 40 (v)] A multiplex signalling system includes an arrangement for generating a series of frequencies equally spaced in the frequency band in which a train of pulses modulates a basic frequency producing a series of modulation frequencies separated by a frequency interval equal to the repetition frequency of the pulses and spreading on either side of said basic frequency. In the transmitting arrangement shown in Fig. 2, 1 is a pulse generator and 2 a sine wave generator the outputs from which are mixed at 3 to give a series of frequencies which are separated by the pulse frequency. For a four channel system, four desired carrier frequencies are selected by filters 4 ... 7 and modulated at 8 ... 11 by signals applied at terminals 81 ... 11<SP>1</SP>. The signals are combined and amplified at 12 and then fed to a radiating system TA12. For a large number of channels, separate final amplifiers and aerials may be used. If it is desired to radiate a very high frequency, the combined signals may be heteradyned by a local oscillator to raise the frequency to the desired value. To send the same signal through all channels, the pulses of generator 1 are modulated in duration, which gives an amplitude modulated signal in the outputs from filters 4 ... 7. A suitable receiver is described, Fig. 3 (not shown) in which the signals of all the channels are amplified together and converted to a series of convenient intermediate frequencies for separation by filters and subsequent detection.