Patent GB-753546-A (GB)
Title: Improvements in or relating to broad frequency band transmission systems
IPC: H04B1/74
Filed: 1954-02-05
Abstract: 753,546. Repeater systems. WESTERN ELECTRIC CO., Inc. Feb. 5, 1954 [Feb. 6, 1953], No. 3442/54. Class 40 (4). In a two-way broad-band transmission system employing for each direction of transmission a plurality of transmission lines which are divided into a number of tandem repeater sections each of which comprises two or more working lines and a further line available as a spare or reserve line, switches at both ends of each section, for substituting a section of spare line for a section of faulty working line provided the spare line is shown by the level of pilots transmitted thereover to be functioning satisfactorily, are operated as a result of abnormal changes in the level of system pilot currents in that section. In a section of the lines wl1 wl2, and sl. Fig. 2, for West-East transmission, line wl1 which has prior claim to the use of the spare line sl in an emergency, is coupled to the spare line over a hybrid transformer H1 and a transmitting end switch S1, and in consequence the system pilot signals which may serve also for gain control purposes are present on the spare line. Pilot indicators PI1, PI2, PI3 control a circuit CC which, in the event of a fault, sends a signal to receiver switches RS, and an initiating signal to the transmitting-end switching-control circuit TC to effect switching if it is necessary at that end, i.e. if the fault is in working line wl2. The control circuit TC returns a verifying signal to the receiver switches RS and the combined signals from CC and TC together with a direct current signal from pilot indicator PI3 actuate appropriate switches at RS to complete the substitution. The signals from circuit CC to circuit TC identify the faulty line and a fault on the spare line sends a blocking signal to prevent switching by faults on the working line whilst the spare line is faulty. In the transmitting and receiving control and switching equipment for a two-way station, Figs. 3-6, the pilot indicators, for West to East signals, fed over transformers such as T1, T2, comprise pilot current filters F1-F8, a common amplifier A1, and rectifiers RE1-RE4 for rectifying the pilot current outputs from filters F5-F8 respectively. The rectifier outputs control gating circuits. Fig. 7, comprising rectifiers 17 and 18 biased by D.C. potentials applied over resistors 25, 26, which circuits are arranged to apply the output of signalling oscillators, STO to all the East-West lines via pads 28-30, filters 31-33 and hybrid transformers H1<1>, H2<1>, when an abnormal pilot on a West-East line is indicated. The switching current is received at the preceding station by filters F9-F11, amplified at A2, selected by the appropriate filter F12-F15 and rectified to control transmitting switching control circuits TS1, TS2 or emergency switching control circuit EC. The appropriate buffer amplifier VB1, VB2, in the output of the verifier oscillator VO, is unblocked after a 50 millisecond delay in circuit DC1 or DC2 by the operation of circuit TS1 or TS2 and in both cases the verifying signal is returned to the receiving end of the section via spare line sl, the oscillations being fed to the line over the appropriate filter F17, F18, hybrid transformer H1, H2, and switch S1, S2, respectively. The priority of the preferred working line is achieved by the transmission to the transmitting end of the faulty section of a priority establishing signal in addition to the fault identifying signal. The additional signal is generated in the switching initiator SI1 of the preferred line and at the transmitting end the signal which is selected by filter F12 and rectified unblocks circuit EC and the switching control circuit TS1 is thus prevented from operating, i.e. switch S1, Fig. 2, is prevented from opening. Emergency buffer circuit EB is -also a gating circuit and is opened, after a delay, when both the preferred working line wl1 and the spare line are faulty to send a 50 kc/s. signal in the reverse direction to tie the spare line sl to the working line wl2. Due to the absence of pilot current on the preferred and spare lines in the following sections the spare line in those sections is coupled to the second working line. Electromagnetic relays for effecting the switching are described with reference to Figs. 8 and 9 (not shown). The switching may be effected by make-before-break switches of the mercury or reed type, or alternatively the switches may be electronic. The relays not only switch the lines but by means of auxiliary contacts connect dummy terminations to otherwise disconnected lines. Auxiliary relays SR1 SR2 in the transmitting switch control circuits open the connection between the switching initiating circuit SI1 and transmitting switching control circuit TS1 when the spare line sl is also faulty. The arrangement described permits the taking over of the spare line in the event of a fault in the preferred line even though it may be in service in place of the non-preferred line. Filters 89- 90 limit switching signals to the ends of the faulty section. The Specification includes examples of section lengths, repeater spacing and suitable pilot and switching frequencies.