GB509820A - Improvements in or relating to electric signalling systems - Google Patents

Abstract

509,820. Repeating systems ; multiplex systems ; valve circuits. STANDARD TELEPHONES & CABLES, Ltd. (Deloraine, E. M., and Reeves, A. H.). Nov. 19, 1937, No. 31889. [Class 40 (iv)] [Also in Group XL] Relates to signalling systems in which the instantaneous values of a speech wave or the like are represented in the transmission channel by the intervals between impulses (or trains of carrier current) which are transmitted in pairs and comprises (1) '' trigger-type " repeaters in which a valve trigger circuit has one stable condition and in response to an applied signal impulse assumes a second condition of equilibrium for a definite time independent of the duration of the signal impulse; (2) "synchronous " repeaters in which signal impulses are applied to a relaxation oscillation generator having a natural frequency close to the frequency of the signal impulses and bring it into step ; (3) " synchronous " repeaters in which signals in the form of short trains of carrier frequency current are applied to a valve which is generating oscillations at the carrier frequency, these oscillations being periodically quenched at substantially the frequency of the signal trains; (4) terminal apparatus for converting speech &c. into impulses of the lastmentioned kind, the speech being applied to an additional electrode of a valve which generates carrier frequency oscillations, which are periodically quenched ; (5) a multiplex system in which a distributer device controls a number of valves, each of which converts speech into impulses, so that they produce their impulses in turn. Where several repeaters are used in tandem they are so spaced that the system is automatically conditioned to transmit in the direction of signals. Two or more repeaters or valves may be permanently connected in parallel so that communication is not interrupted if one of them fails. In some cases, frequencies of the order of 10,000 mega,- cycles are involved. Transmission may be by wire, wireless or dielectricguide. Trigger-type repeaters. The circuit shown in Fig. 1 comprises a double triode with the left-hand grid connected to the righthand anode over a resistance B and the right-hand grid coupled to the lefthand anode by a condenser S having a leak resistance T. In the normal state the left-hand anode current is low, but when a signal arrives the arrangement snaps over to the other condition for a period depending on the values of Sand T and the bias voltages and then snaps back. "Synchronous" repeaters. In one arrangement, Fig. 3, for direct current impulse signals, a muttivibrator is coupled to the line as shown and is pulled into step by signals in either direction. A rectifier K acts as a short circuit to the impulses of one polarity. In another arrangement, Fig. 4, in which the signal impulses are trains of carrier-frequency oscillations, a valve A is connected to oscillate at the carrier frequency and is made periodically active and quiescent at a frequency close to the impulse frequency by a resistance condenser circuit. Signals from the cable or antenna H are demodulated by this arrangement and the periodic activating and quenching is brought into step with the received impulses. An equivalent arrangement for very high frequencies is shown in Fig. 5, the valve in this case being a " solid anode " magnetron which is coupled by means not shown to a dielectric guide. Terminal apparatus, Fig. 7. This operates in the same way as the synchronous repeater shown in Fig. 4, except that the phase of the trains is controlled by rectified speech currents applied to an additional electrode instead of by received signal impulses, the arrangement being such that the phase of the trains is always advanced in the presence of speech. Multiplex signalling. Speech channels may be multiplexed by causing them to modulate suitably separated carriers and then signalling the instantaneous amplitudes of the complex resultant wave by means of impulses. As shown in Fig. 8, however, the speech wave in each of twelve channels is separately signalled in pulse form, each channel in turn occupying the line for an instant under the control of synchronous devices A, B which are preferably common to -a number of lines. Multi-vibrator C for channel 1 oscillates at 10,000 cycles and receives synchronizing impulses at this frequency from the device A. The time at which the multivibrator cycle starts with respect to this impulse is modified by the speech wave. At the receiving end a multivibrator L<SP>1</SP> is brought into step with the signals and gives impulses to the primary of transformer M. The duration of these impulses is proportional to the amplitude of the original speech wave and speech signals therefore appear in the secondary circuit. The other channels operate in turn in the same way. The functions of the multivibrators C, L<SP>1</SP> are transposed by a switching device which may be under speech control and which modifies their natural frequencies and their starting times with respect to the synchronizing impulses in the absence of speech. Specifications 344,444 and 363,403, [both in Group XL], are referred to.