GB652378A - Improvements in and relating to multi-channel pulse communication systems - Google Patents

Abstract

652,378. Multiplex pulse signalling. GENERAL ELECTRIC CO., Ltd., FARREN, L. I., and HEAD, N. E. Sept. 12, 1947, No. 25093. [Class 40 (v)] In a multi-channel pulse signalling system, synchronizing pulses have a regularly recurring characteristic feature and are modulated at a frequency equal to the recurrence frequency of the characteristic frequency divided by an integer. A system is described in which said feature is the leading or trailing edge and the synchronizing pulses are modulated in duration at channel pulse recurrence frequency. The channel modulators each deal with a plurality of channels forming a group, e.g. one may deal with channels 1, 11, 21, &c., as described in Specification 652,357, and the synchronizing pulse recurrence frequency is the channel pulse recurrence frequency multiplied by the number of channels in a group. The modulator is a cathode-ray tube of the type described in Specification 619,785 and the synchronizing pulses are produced by the interaction of the rotating beam with a triangular slot 2. The regularly recurring trailing edge of the pulses is defined by the radial edge 3, the duration being modulated by a channel recurrence frequency sinusoidal signal applied to the deflecting plate MD1, which varies the radius of rotation of the beam and hence the timing of the leading edge of the pulse determined by the inclined edge 5. Alternatively, the amplitude of the pulses may be modulated by an electrode positioned in the path of the beam. A similar electrode may also be used to vary the amplitude of the pulse at a predetermined regularly recurring position thereon, to provide the characteristic inveriable feature of the pulses. Receiver.-The synchronizing pulses are separated at the receiver by a pulse duration discriminator, as they are all of greater duration than the channel pulses. A following differentiating circuit produces negative pulses corresponding to the trailing edges, these being selected and used to synchronize the channel groups at the demodulator. The discriminator also feeds a low-pass filter yielding a synchronizing output at channel pulse recurrence frequency.