Patent GB-668272-A (GB)
Title: Apparatus for pre-correcting telegraph signals to compensate for characteristic distortion in transmission over a line
IPC: H04L25/49
Filed: 1948-01-02
Abstract: 668,272. Code telegraphy. BAYARD, H. M., and ROQUET, R. J. C. Jan. 2, 1948, No. 166/48. Addition to 652,601. [A Specification was laid open to inspection under Sect. 91 of the Acts, Feb. 23, 1948.] Class 40 (iii). Apparatus for precorrecting telegraph signals by delaying the retransmission of each signal element by a time interval dependent on the combination of a predetermined number of signal elements is modified to deal with the precorrection of trivalent signals by means which operate so that each trivalent element is represented by a combination of two bivalent elements which are precorrected separately according to the nature of the preceding trivalent elements and are subsequently combined to provide the precorrected trivalent signal element. The arrangement may be such that the trivalent signal modulation is effectively subdivided into two separate bivalent signals which are individually precorrected as bivalent modulations or signal trains and are then recombined to form the precorrected trivalent train of signal elements. In the arrangement shown in Fig. 3, the incoming signals applied to a relay ME are fed to two threeposition relays F1, Fl and to operating windings of relays G1, G2, which are provided with biasing windings fed from a local battery so that when the line current is zero, the armatures A1, A2 are operated respectively to positive and negative voltage sources. The positive and negative signal elements overcome the biasing windings to operate the two armatures A1, A2, to the positive or negative voltage source. The incoming signal element is also applied after a predetermined interval via a distributer D1 to a relay E1 which controls two sets of relay windings F2, F2<SP>1</SP>, F2<SP>11</SP> and the voltage set up on the relay E1 is also applied via a distributer D2 to a relay E2 which controls two identical sets of relay windings F3, F3<SP>i</SP>, F3<SP>ii</SP>, F3<SP>iii</SP>, F3<SP>iv</SP>, F3<SP>v</SP>. The relative positions of the conducting segments P1, P2, on the distributers D1, D2, are such that the three separate relay groups F, F2 ... F3 ... are operated according to the signal element to be precorrected and the two preceding elements. The relays are maintained in their actuated positions for the remainder of the period of a signal element by subsidiary distributers D1<SP>1</SP>, D2<SP>1</SP>. The selective (and identical) settings of the relays Fl, F2 ..., F3... establish a circuit from contacts Al, A2, through distributers D3, D4, connected at points B1, B2, to relays RE1, RE2. The distributers provide appropriate delays according to the connection of their conducting segments to the connecting points 1 ... 9, 11 ... 91. The positions of the armatures of the relays RE1, RE2 correspond respectively to the polarities imposed at the points Al, A2 and with both armatures of the relays RE1, RE2 in the right-hand position, a precorrected positive impulse will be sent from battery 5A to the line VT. For a zero impulse, the armatures of relays RE1, RE2 are in right-hand and left-hand positions respectively, and a change to the zero condition will be effected at the precorrected instant. At an instant at which the incoming signal modulation is not changed, that is the signal element to be transmitted is the same as the previous elementno correction is necessary, and this is provided for by a break in the circuit at the appropriate contacts engaged by the armatures of the relays F1 and F2, F2<SP>1</SP>, F2<SP>11</SP>. It is indicated in the case of the precorrection of a signal element in accordance with two preceding elements that the nine possible combinations can be represented by one condition selected from each of two sets of three designating conditions I, II, III and A, B, C, viz. that at the characteristic instant the signal element changes from negative to positive, zero to positive or negative to zero and that the penultimate signal is positive, zero or negative. An arrangement based on this consideration is indicated in Fig. 4. The armatures' F1, F1<SP>1</SP>, F1<SP>11</SP>, are positioned corresponding to the element being transmitted and the two pairs of armatures F2, F2<SP>1</SP> and F3, F3<SP>1</SP> are positioned according to the two previous signal elements. The segments 1 ... 9, engaged by the distributers #1, #1<SP>1</SP> are selectively connected together so that a circuit is completed from the point Al to B1, at an appropriate point in the distributer cycle in accordance with the positioning of the armatures by the three signal elements in question. The apparatus shown in Fig. 4 is duplicated so that the two corrected impulses can be superimposed to form the precorrected trivalent modulation. Fig. 5 (not shown) is a modification of Fig. 4, and is arranged to provide precorrection in respect of three preceding signal elements. In a further modification, Fig. 6, in which the signal modulation is segregated into two constitutent bivalent modulations which are corrected separately, the corresponding bivalent signal elements are reproduced by the contacts K, K<SP>1</SP>, from which relays E<SP>1</SP>, E1<SP>1</SP> are actuated after a delay of an elementary period. Relays E2, E2<SP>1</SP> are operated from the armatures of relays E1, E1<SP>1</SP> with a delay of an elementary period so that the pairs of armatures conjointly represent the trivalent modulation. Relays C0, C1, C2 are operated when the armatures K, K<SP>1</SP> or the' armatures of relay E1, E1<SP>1</SP>, or E2, E2<SP>1</SP>, are in opposite positions. In addition a relay # is operated when the armatures of the relays E1<SP>1</SP>, E2<SP>1</SP> are in opposite positions. The selective operation of the relays C0, C1, C2, F connect identical condensers V, V<SP>1</SP> respectively to a resistance 1 ... 9 and 1<SP>1</SP>... 9<SP>1</SP> to effect appropriately delayed operation of the relays RE, RE<SP>1</SP> in accordance with the polarities set up by the armatures K, K<SP>1</SP>. In a modification of Fig. 6, Fig. 9 (not shown), in which the delay required is relatively great for some of the signal combinations, additional armatures are provided to close an auxiliary delay circuit in response to the respective signal combinations and this delay is added to that provided by the normal delay circuits. A further modification, Fig. 10, is based on the assumption that when the signal combinations are designated by two conditions, one derived from each of two sets of three conditions I, II, III and A, B, C, the precorrection delay for a signal combination is approximately equal to the sum of delays associated with the component designating conditions. The selective operation of the armatures C0, C connects a condenser V(I, II, III) and one of the resistances RI, RII, RIII in series with the winding of relay RE(I, II, III) and the selective operation of the armatures C2, F connects a different condenser V(ABC) and one of the resistances RA, RB, RC in series with a relay RE(ABC) which is operated with an appropriate delay following the delayed operation of the relay RE(I, II, III). Modifications of Fig. 10, operating on the same principle, are described in connection with Figs. 11-14 (not shown).