Patent GB-402780-A (GB)
Title: Improvements in and relating to methods and apparatus for use in telegraphic signalling systems
IPC: H04L27/06
Filed: 1932-05-28
Abstract: 402,780. Code telegraphy. REGNAULD DE BELLESCIZE, H. J. J. M. DE, 47, Boulevard de la Seine, Neuilly-sur-Seine, France. May 28, 1932, No. 15165. Convention date, May 29, 1931. [Classes 40 (iii) and 40 (v).] Signal impulses in Baudot or like telegraphy have a period To, Fig. 6, as transmitted, but at the receiver each impulse is applied to a storing device for a time T ; thereafter the storing device feeds a registering device for a time T1; and then it is damped or discharged during a time T2. Since (T+T1+T2 is only slightly less than 2 To, two receivers dealing with alternate impulses are employed. In order that desired signals may be favoured in comparison with undesired signals, the selecting circuit has a large time constant. It is shown that interference between channels does not occur provided that the frequencies in different channels are given by (f + nF) for different integral values of n, where F is the signal frequency in bauds of the slowest channel, the speed in the nth channel being nF. There may be one d.c. channel. Homodyne method of reception. Signals of carrier frequency f, (f + F), (f + 2F) .. , where F is the impulse frequency in bauds are applied via line 60, Fig. 15, to amplifiers 61, 86 .. serving different channels. In the channel shown, signals of carrier frequency fare demodulated by homodyning with oscillations of frequency f from a local source 62, synchronized as described in Specification 392,567. The d.c. product is applied through amplifier 33 to the signal-recording system. The highfrequency products of demodulation are filtered out by a filter 29, while the products of frequency F, 2F .. from other channels are so phased that the time-integral of their effect is zero (Figs. 11 .. 14, not shown). The rectified marking impulses passing through valve 33 are dealt with alternately by distributors 64, 64<1> whose operations are similar but differ in phase by 180‹ ; they are indicated in Fig. 5 (not shown) and at the upper and lower parts respectively of Fig. 6. The rectified marking impulse is applied for a time T through segment 37 and brush 36 to storing-condenser 35. The condenser potential is then applied for a time T1 through brush 36 and segment 38 to the grid of valve 42, which operates relay 85 so that an impulse is recorded through armature 43. Finally the condenser is discharged for a time T2 through brush 36, segment 39 and resistance 40. The Specification describes how to adjust the contacts 41, 47 with the aid of switches 49, 51, 45 (which are normally in the positions shown) and milliammeters 52, 46. The time constant of the condenser circuit is made large in comparison with the signal period, in order to eliminate parasites, In a simplified modification (Fig. 9, not shown) the period T1 is omitted; the condenser is charged during the first part of a signal period and discharged directly through the relay 85 during the remainder. Direct-current signals. In a further modification f = o, so that the frequencies employed are zero (direct current), F, 2F . .. In the d.c. channel the line 60 is connected directly to the grid of valve 33, Fig. 15 and the large timeconstant of circuit 34, 35, serves to eliminate parasites. Synchronism. The transmitting distributors for the various channels are geared together and a synchronizing space impulse is sent out after every twenty-one signal periods. At the receiver, all impulses are fed to an amplifier 63 controlling an armature 75 which at each change of polarity interrupts momentarily the arm 77 of a circuit comprising an'auxiliary winding 80 of a motor 65 which drives the distributor 66, 67. So long as brush 71 is on a segment 66 or 67 when the interruption at 75 occurs, this interruption has no effect and the motor runs fast : but if brush 71 is on insulation at that moment, the interruption is effective and the motor runs slow. The brush 71 tends therefore to be in the position shown at the moments when the interruptions due to changes of signal polarity occur. Receiver employing resonators. In a modification, Fig. 17, the oscillations pass from line 95 to distributors 93, 102, which serve different channels. In each channel the impulses are fed alternately to two valves, one of which shown at 94. Valve 94 excites a mechanical resonator 97 for a time T, after which the distributor contact at 93 is opened, that at 99 is closed, and the resonator excites a valve 100 during a time T1. The resonator is then, during time T1, mechanically damped by means 101 operated by the distributor. The resonator 97 is tuned to the channel frequency, and forced vibrations from other channels have an amplitude which waxes and wanes but falls to zero at the instant when contact is broken at 93, in consequence of the fact that the channel frequencies differ by integral multiples of the lowest impulse frequency. Specification 134,585, [Class 40 (v), Wireless signalling &c.], also is referred to.