Patent GB-917410-A (GB)
Title: Electric signal receivers
Inventor: STARR TOM
IPC: H04Q1/38
Filed: 1960-10-01
Abstract: 917,410. Electric selective signalling systems. ERICSSON TELEPHONES Ltd. Oct. 12, 1961 [Oct. 1, 1960], No. 33761/60. Class 40 (1). A receiver comprises first and second input terminals to which first and second signal voltages may be applied, a first detector connectable to the first input terminal and comprising a plurality of threshold devices each responsive at a different level of the first signal voltage other than zero, a switch for connecting a second detector to the second input terminal after reception of a first signal voltage, the second detector also comprising a plurality of threshold devices each responsive at a different level of the second signal voltage, and means for selecting an output terminal in accordance with the numbers of threshold devices made responsive in the two detectors. In a first embodiment, Fig. 1, a sending station (not shown) conditions the receiver for reception by connecting a loop across input terminals A, B. Power source S is then connected over x2 (operated), bc1 (released) and pa2 (operated) to B and the sending station, so that the first signal voltage is applied to A and over pa1 (operated), cr1 (released) and xl (operated) to transistor threshold devices G1, H1, I1. These transistors are normally cut off and transistors G3, H3, I3 are normally conducting so that G, H, I are operated. If the first signal voltage is " high," all relays G, H, I are released, if it is " medium " relays H, I are released and if it is low relay I only is released. If the first signal voltage is nominally zero, none of G, H, I are released, but after a predetermined time relay X releases over i3 and r12 to connect S to A and the second signal voltage which now appears at B is connected to threshold devices J1, K1, L1, Fig. 2 (not shown), comprising the second detector. Thus, the first signal voltage may have any one of four values, but only three threshold devices are required in the first detector. Relays J, K, L are released selectively in response to the second signal voltage, and contacts of the relays G-L are used to mark one output terminal, Fig. 4 (not shown). In the receiver of Figs. 6, 7 switching transistor X1 is initially conducting and the first signal voltage is applied from A to G1, H1, I1 via F1. Transistor X2 is cut off by mono-stable circuit M1, M2 which is initially in its stable state with M2 conducting. In this receiver the first signal voltage cannot be zero since the second signal voltage cannot be received until AA, Fig. 7, has operated to trigger circuit M1, M2 over aa1 and thus cut off X1 and render X2 conductive. Since M1, M2 eventually returns to its initial state of its own accord, however, the second signal voltage may be zero in this embodiment. In response to the two signal voltages certain of bi-stable circuits G4, G5- 14, 15 and J4, J5-L4, L5 (not shown) are switched to the state with I4 &c. conducting. Thus a number of gates g1-g9 are opened and their associated capacitors C1-C9 are charged, as is also capacitor C0. Terminals o1-o0 are connected to a homing switch U in such a way that the wiper scans the contacts corresponding to the highest voltage combinations first and comes to rest at the first marked contact. Switch U may transmit a pulse for each step taken. By providing a further input to the gates from points P, only one of terminals o1-o0 may be marked, Fig. 8 (not shown). Either receiver may be used to receive a sequence of first and second signal voltages and mark a combination of output terminals in response thereto by employing suitable distributing arrangements.