Patent GB-341399-A (GB)
Title: Improvements in telegraphic receiving systems
Filed: 1929-10-04
Abstract: 341,399. Code telegraphy. WESTERN ELECTRIC CO., Ltd., Bush House, Aldwych, London.-(Bell Telephone Laboratories, Inc. ; 463, West Street, New York, U.S.A.) Oct. 4, 1929, No. 30135. [Classes 40 (iii) and 40 (v).] In a synchronous telegraph system in which signals of unit length are so attenuated that they are not effectively received, the missing signals are interpolated by a number of independent polarized relays of which the windings are connected to the line in succession by a distributing apparatus. The contacts of the relays are connected to a printing or relaying apparatus so that impulses of alternate positive and negative polarity are impressed on the printing magnets or relays when no effective impulse is being received. The receiving system embodies apparatus designed so that the first derivative with respect to time of the incoming impulses is applied through a distributer arrangement to the windings of the receiving relays, during a part only of the receiving time. Transmitting arrangements. Impulses are sent from groups of transmitters at station X to a cable 20 by a distributer 21 comprising continuous and segmented rings, in which the segments are interspersed so that an impulse from a transmitter A is followed by an impulse from transmitter B, until all the impulses from the first group of transmitters have been sent. To obtain a balance of polarities the battery leads of each group of transmitters are reversed at points between the adjacent groups. Receiving arrangements. At the receiving station Y the impulses from an amplifier 22 are applied to a circuit embodying a condenser 23 and a small resistance 24 so that the first time-derivatives of the received impulses are applied to the relays 27, 28, whose windings are connected to the amplifier 22, and to alternate segments of a receiving ring set 26. The corresponding contacts of the relays are connected to the positive and negative poles of a battery 33 and the armatures to printing ring sets 29, 30 through brushes 31, 32. With the armatures in the positions shown, alternate impulses of positive and negative polarity are impressed on the printer magnets provided that no effective signal is received, and for the printers A<1>, B<1> the printer magnets associated with relay 28 are operated since a circuit is closed from negative battery 33 through the left-hand contact armature of relay 28 and brush 32 to positive battery 35. The operations for printers C<1>, D<1> are reversed since the printing magnets are reversely coupled as regards polarity to the batteries, 34, 35. In Fig. 3 the diagrams a, b, c show the transmitted impulses, the incoming signal wave and the first derivative of curve b with respect to time. The diagram f indicates the curve of the impulses applied to the printer magnets, In operation, as. brush 25 passes over segment A1, no impulse is applied to relay 27 and since a circuit extends from positive battery 33 to positive battery 34, the magnet All does not operate. On reaching segment B1 the relay 28 is not operated, and current flowing from negative battery 33 to positive battery 35 operates the printer magnet B1<SP>1>. As no impulse effective on the relay windings is received, the same cycle of operations is repeated on printer magnets A2<SP>1> and B2<SP>1>. When the brush reaches segments A3 a negative impulse at the second unit of a signal of two units is applied to relay 27 and operates its armature to the left hand or negative contact. As brush 31 reaches segment A3<SP>1>, current will flow from negative battery 33 to positive battery 34 and will operate the magnet A3<SP>1>. On reaching B3, the brush will apply a positive impulse to relay 28 and as its armature is operated to its positive contact, no current will flow through the printer magnet as brush 32 passes over segment B3<SP>1>. As the brush passes over segments A4, B4, only the magnet A4<SP>1> is operated. A positive impulse applied as the brush reaches segment A3 operates relay 27 to its positive contact and magnet A5<SP>1> is not operated, and since no impulse is applied to relay 28 engaging its positive contact the printer B3<SP>1> will not be operated. On reaching C4, a negative impulse operates relay 27 to its negative contact but as brush 31 reaches segment C1<SP>1> the printer magnet does not operate since the leads from printers C<1>, D<1> to the batteries 34, 35 have been reversed. On engaging the segment D1, a negative impulse operates relay 28 to the negative position but again the printer magnet does not operate. The curve f of impulses applied to the printing magnets is similar to curve a but is displaced by an interval corresponding to a signal impulse of unit length. Alternative receiving arrangements. The arrangement in Fig. 4 differs from that in Fig. 2 by the introduction of two thermionic valves connected in series opposition between the amplifier 22 and each of the relays 27, 28. When no impulse is received the space currents in the valves 37, 39 and 47, 48 are balanced so that the relays 27, 28 are not operated. If, for example, a negative potential is applied by the brush 25 to the grid of valve 37, normally biassed negatively by battery 38, the grid becomes more negative and a negative charge is stored on condenser 36. The normal space current in valve 37 is decreased. The grid of valve 39 is negatively biassed by battery 40 but resistance 41 and condenser 42 make the grid less negative with consequent increase of space current in the valve 39. The windings of relay 27 shunted in series by resistances 44, 45 are connected to the plate circuits of the valves 37, 39 and the difference in the space currents causes a voltage change across the windings of relay 27 which is operated to its left hand or negative contact. When the brush 25 reaches the segment B3 a positive potential is applied to condenser 46 and the grid of valve 47. In this case the armature of relay 28 is operated to its positive contact. To provide a balance across each relay, the plate battery 53 is adjustably connected to a resistance 54. Alternative arrangements Figs. 5, 6 (not shown) are similar to Fig. 4 except that single printer-ring sets are employed and the segments are either interspersed or consecutive for each transmitter. The printing battery is located between the continuous ring and the armatures of the relays, and the printing magnets are connected between the segments and the relay contacts. The arrangement shown in Fig. 7 differs from that of Fig. 4 as regards the input circuit to the ring and valve relays. An impulse coil 62, as described in Specification 312,338, is employed between the cable 20 and a vacuum tube amplifier 63, to provide the derivative impulses which are amplified and passed through a blocking condenser 75 eliminating the direct current component. A modification of Fig. 7 is shown in Fig. 9 in which transformers 64, 65 with primary windings 66, 67, and secondary windings 68, 69 are connected between the cable and the amplifier 63. Direct current flowing through a resistance 72 and biasing windings 70, 71 in opposite directions relative to the transformers 64, 65, bias the latter as described in Specification 312,338, [Class 40 (iii), Telegraphs, Electric]. The secondary impulses are shaped by a resistance capacity network 73, and a blocking condenser 75 prevents the plate battery from being short circuited.