Patent GB-623415-A (GB)
Title: Improvements in or relating to multichannel electric pulse communication systems
IPC: H04B7/17
Filed: 1946-09-27
Abstract: 623,415. Multiplex pulse signalling ; pulse discriminating circuits. STANDARD TELEPHONES & CABLES, Ltd. Sept. 27, 1946, No. 28952. Convention date, Feb. 26, 1945. [Classes 40 (v) and 40 (vi)] A multi-channel electric pulse communication system comprises means for transmitting a plurality of pulse trains on a common carrier frequency, the pulses of each train having a width and recurrence frequency characteristic of the channel which it represents, and the receiver is provided with pulse width selective means for separating the pulses of a given channel. The invention avoids the need for synchronism between the signals of the different channels, the final composite pulse train being such that certain pulses of one train may be superimposed on pulses of other trains. The receiver may be tunable to the appropriate carrier frequency, and also to the desired pulse width and repetition frequency, so that any desired channel may be selected from one or more transmitting stations. Fig. 5 shows the elements of a suitable receiver, incorporating channel selective means. The composite pulse waveform after R.F. amplification and detection is passed to differentiator 37, which produces positive or negative derivative pulses in response to each abrupt change in the leading or trailing edge of the wave. The output from differentiator 37 is passed to clipper 45, via lead 44, and an output equal to the inverse of the differentiator 37 output and delayed by a time equal to the pulse width of the desired channel is also passed to clipper 45 via invertor 47 and delay device 48. These two outputs are combined in clipper 45, and the arrangement is such that for pulses of the desired width, the derivative pulses of the leading and trailing edges are combined to produce an impulse of twice the normal amplitude. Clipper 45 is biassed to select only these longer impulses, so that only signal pulses of the desired width as determined by the amount of delay introduced by device 48, are passed on to the T.M. demodulator 55. The impulses taken from clipper 45 have the same time relation as the original signal pulses of the channel concerned, so that time modulation may be used. The output from demodulator 55 is passed through a low-pass filter to a utilisation device 57. Alternatively, other types of pulse width discriminator circuits may be employed in the receiver and reference is made to Specification 581,068 and 593,511. Several transmitters operating on the same frequency and each having a characteristic pulse width and pulse recurrence frequency may be provided, or one transmitter may be used to transmit the combined output of several channels similarly characterised. A suitable form of pulse time modulator is described (Fig. 3, not shown), and reference is made to Specification 600,244. An additional arrangement is described, in which two terminal stations are connected by a series of relay stations multi-channel communication on a common carrier frequency being established either by unsynchronized trains of pulses according to the invention, or by appropriately timing each train of pulses to form an interleaved train. Signal pulses from a mobile station such as an aeroplane, may then be transmitted for reception by one of the relay stations to be inserted into the relayed signal trains for onward transmission and demodulation at one of the terminal stations.