Patent GB-248822-A (GB)
Title: Improvements in submarine cable and like telegraph systems
IPC: H04L25/00
Filed: 1924-12-06
Abstract: 248,822. Western Electric Co., Ltd., (Western Electric Co., Inc.). Dec. 6, 1924. Restoring or modifying imperfect signals; eliminating effects of disturbing currents; duplex telegraphs. -Distortions of the frequency components of high-speed telegraphic signals received over a submarine cable are corrected by shaping elements having different proportional correcting effects on amplitude distortion and phase distortion. Figs. 1 to 3 show duplex arrangements in which the recorder R is connected to the apex of the duplex bridge through shaping elements associated with valve amplifiers. In the arrangement of Fig. 1 an element A effecting mainly phase corrections and an element B effecting mainly amplitude corrections precede the valve amplifier, and are connected by a variable condenser 17 shunted by a variable high resistance 18. The element A is a suitably adjusted magnetic shunt comprising a variable inductance 19 and a variable resistance 20. The element B is a similar but differently adjusted shunt comprising a variable inductance 21 and a variable resistance 22. The valve amplifier comprises four valves 1A1, 1A2, 1A3, 1A4, resistance-coupled as shown. A battery 30 is provided to counteract the zero signalling current through the recorder R. In the arrangement of Fig. 2 a magnetic shunt 39 similar to the element A, Fig. 1, effecting mainly phase corrections precedes the first valve 2A1, and a network 42 effecting mainly amplitude corrections is arranged between the valves 2A1 and 2A2. This network comprises an inductance coil 45 to an intermediate point of which is connected the plate of valve 2A1. variable resistances 44, 46, 48, and a variable condenser 47. Fig. 3 shows a modificatian of the arrangement of Fig. 2 in which a potentiometer 60 is arranged between the magnetic shunt 61 effecting mainly phase correction and the first valve 3A1, and potentiometers 74 supplied by batteries 75 replace the grid polarizing batteries. The batteries 75 for the valves 3A2, 3A3, 3A4 have their positive poles connected to the grids to neutralize partially the high negative potential due to the drop through resistances 69 and 72. The network 64 between valves 3A1 and 3A2. effecting mainly amplitude corrections, comprises an inductance coil 70, variable resistance 69, and variable, condenser 71. The network 65 between the valves 3A2 and 3A3 comprises an inductance 73 and a variable resinstance 72. and a similar network is arranged between the valves 3A3 and 3A4. Fig. 4 shows another type of bridge duplex system in which a shielded transformer 86 is used between the bridge and the main shaping and amplifying devices associated with the receiver. A magnetic shunt 84 similar to the shunt 39. Fig. 2, and provided with a shield 85 is connected across the transformer primary. The amplifier comprises a four-valve main section RA and a two-valve auxiliary section RRA, and a switch 106 is provided to connect the section RA to a recorder R or to the section RRA for the operation of a relay REL. The shaping network 99 between the valves 4A1 and 4A2 comprises an auto-transformer 96, variable resistance 97, and variable condenser 98, and similar networks 100, 101 are arranged between the succeeding valves, these networks 99, 100, 101 being selective to successively-higher frequencies. The input circuit of each of the valves 4A1, 4A2, 4A3, 4A4 includes a series resistance 91 and a condenser 92 crossconnected between the grid and the filament for eliminating high-frequency interference. The single valve 4A4 is preferably replaced by two valves in parallel. The relay REL is provided with an additional winding 119 energized from battery 121 to compensate for the field due to the normal non-marking plate current of valve 4A6. Separate leads are provided in the section RA for the connections to ground and to the filamentheating battery 93 to prevent pick-up and like interference. Minor modifications of the shaping and amplifying arrangements of Figs. 1 to 4 are described in the Specification. In a further modified arrangement, shown in Fig. 6 as applied to a simplex system, phase correction is effected mainly by a magnetic shunt 61 similar to that shown in Fig. 3 preceding the first valve 6A1. Amplitude correction is effected mainly by a network 184 between the valves 6A1 and'6A2, comprising a variable condenser 187, a variable resistance 188, and an auto-transformer 189. This network functions also to amplify the frequency components to different degrees to correct for unequal attenuation, and to eliminate undesired frequencies, and is placed as shown in the input circuit of valve 6A2 to enable the use of higher potentials in the plate circuit of valve 6A1. The network 193 between the valves 6A2 and 6A3 comprises a variable inductance 196 shunted by a variable resistance 197 and in series with a variable condenser 290 connected across a grid leak resistance 198. This and a similar network 202 between the valves 6A3 and 6A4 function as lowpass filters. Fig 11 shows a modification of the shaping network preceding the first valve 6A1, Fig. 6, this network functioning to amplify the higher frequency more than the lower frequency components, as well as to effect the main phase corrections. The cable is connected to an intermediate point of an auto-transformer 358 through a variable condenser 355 and a variable shunt resistance 356 which, however, are eliminated by closing a switch 357 except when the highest signalling speeds are in use. The auto-transformer 358 and a series resistance 359 are in shunt across a potentiometer 365 from which the valve amplifier is supplied. A switch 364 enables a condenser 363 to be inserted in this circuit to eliminate earth current effects, and a switch 362 enables the intermediate point of auto-transformer 358 to be' connected to ground through a variable condenser 360 shunted by a variable resistance 361 to eliminate high-frequency disturbances. Figs, 8 and 10 show a suitable construction for the transformer 86, Fig. 4. The core 300 is built up of sheets of " permalloy " and is provided with a small air-gap, not shown, in the central leg, preferably near one end. The primary winding comprises two pairs of pancake coils 301. each pair being enclosed in a copper shield 303. The secondary winding comprises one pancake coil 302 arranged between the pairs of primary coils, and enclosed in a copper shield 304. A lead 305 is connected to each shield at a point diametrically opposite a slot 306 in the shield, the lead from the shield 303 being connected to the primary winding, and that from the shield 304 to ground. The auto-transformer 96, Fig. 4, and 189. Fig. 6, are similarly provided with " permalloy " cores. The auto-transformer 358, Fig. 11 is preferably provided with a core of compressed powdered iron.