Patent GB-652601-A (GB)
Title: Apparatus for pre-correcting telegraph signals to compensate for characteristic distortion in transmission over a line
IPC: H04L25/03
Filed: 1945-04-30
Abstract: 652,601. Code telegraphy. BAYARD, H. M., and ROQUET, R. J. C. April 30, 1945, No. 10903. Convention date, Nov. 18, 1943. [Class 40 (iii)] Apparatus, for pre-correcting double-current telegraph signals to compensate for the characteristic distortion arising in their transmission over a telegraph line, comprises means for delaying the instants at which the signalling circuit is keyed to produce current for the signal elements by intervals depending on the combination or sequence of signal values occurring during a finite number of elementary intervals, i.e. periods each corresponding to a unitary signal element, preceding the impulse whose delay time is to be adjusted. In the operation of one modification the appropriate delay for a signal element is selected by comparing the polarities of the signal elements in the first and second elementary intervals preceding the signal element to be corrected and also of the signal elements in the second and third elementary intervals, preceding the beginning of the interval of the signal element it is desired to correct. In the arrangement shown in Fig. 1 distorted signals arriving over a line ME are applied during a fraction of the signal period by a contact segment P0 of a distributer D0 to a relay E0 whose armature is connected to the outgoing line MP through a " delay " distributer D5 and the operated contact of one of the relays R1 ... R4. The armature of the relay EO is also connected through a segment of a distributer D1 to a relay E1 whose armature is connected over a segment P2 of a distributer D2 to a relay E2. The armature of the relay E2 is connected by a segment P3 of a distributer D3 to a relay E3 and associated relays E<SP>1</SP>1, E<SP>1</SP>2 are effectively connected to the armatures of the relays E0, E1. The segments PO ... P3 of the distributers D0 ... D3 are positioned so that during a single rotation the signal elements appropriate to these elementary intervals are set up on the relays E0, E1, E2 and the impulses corresponding to the three preceding intervals are simultaneously registered on the relays E<SP>1</SP>1, E<SP>1</SP>2 and E3. Six fixed brushes B1 ... B6 connected to contacts engaged by the armatures of the relays E<SP>1</SP>1, E<SP>1</SP>2 and E3 are engaged by sets of studs, I, II, III1, III2 mounted on a rotating cylinder. The sets I, II are connected through rotating brushes shown on the left and the studs of the sets III1, III2 are interconnected in pairs and also connected by four rotating brushes to the polarized relays R1, R2, R3, R4. The arrangement of the studs of the sets I, II and the interconnection of the studs of the sets III1, III2 are such that the same relay R1 ... R4 is operated by the two combinations of three signal elements in which the values of corresponding elements are respectively reversed, e.g. + - + and - + -. The operation of a relay R1 ... R4 corresponding to the three signal elements preceding a signal element to be transmitted connects the transmitting relay RP to the armature of the relay E0 through the associated segment P4 ... P7 of the delay distributer D5 so that the impulse registered by the relay EO is transmitted to the line MP with the appropriate precorrection. The relays R1 ... R4 are reset to their normal positions by a distributer D4. If the signals to be transmitted are free from distortions the distributer D0 can be omitted and the signals applied directly to the relay E0. In a modification, Fig. 2, a signal element received over the line M<SP>1</SP>0 is fed to a relay F1 through a delay device G1 producing a delay corresponding to an elementary signal interval. The signal registered by relay F1 is fed to relays F2, F<SP>1</SP>2 through networks G2, G<SP>1</SP>2 producing a unitary delay and the signals at F2, F'2 are passed to relays F3 ... F<SP>111</SP>3 through devices G3, G<SP>1</SP>3 producing a further delay corresponding to a unitary period. The signal elements corresponding to three successive intervals are therefore simultaneously set up on a relay chain to operate selectively one of the relays S1 ... S4, thereby removing the short-circuit from one of the delay networks Q1 ... Q4 and effecting the appropriate delay in the operation of a relay RP<SP>1</SP> to transmit the signal from the line M<SP>1</SP>0 to the line MP<SP>1</SP>. In a further modification, Fig. 3 (not shown), three successive signal elements are registered on relays by the operation of distributers generally as in Fig. 1. The first and second preceding elements are applied to opposite corners of a rectifier bridge, and the other two corners of the bridge are connected to the ends of a relay winding. The second and third preceding elements are applied to opposite corners of a second bridge which similarly is connected to a second relay. The comparison of the nature of the signal elements of each pair controls the operated or non-operated conditions of the relays associated with each rectifier bridge and contacts engaged by the armatures of the relays effectively control selection of two impedances out of four possible impedances for connection in shunt to the line connecting the receiving relay to the transmitting relay.