Patent GB-657120-A (GB)
Title: Remote fault indicating system for multichannel pulse modulation radio link
IPC: H04B7/17
Filed: 1948-08-20
Abstract: 657,120. Radio signalling. STANDARD TELEPHONES & CABLES, Ltd. Aug. 20, 1948, No. 21980. Convention date, Dec. 11, 1947. [Class 40 (v)] In a multichannel two-way radio pulse communication system having one or more repeater stations, remote fault indication at the terminal stations is provided for by producing at repeater stations, from marker pulses in the transmitted train, delayed indicating pulses falling into an unoccupied channel period, the indicating pulses being suppressed on the occurrence of a fault condition at a repeater. In the system described each repeater uses channel 1 for the indicating pulses but only one repeater at a time transmits these pulses for an interval determined by a clock-controlled switch, a synchronous switch at the indicating point enabling the point from which the pulses originate to be determined. The production of the indicating pulses is controlled by a pick-up aerial in the vicinity of each transmitting aerial at the repeaters. When no signal is present in the output of a repeater receiver, an emergency tone signal is generated and sent from the associated transmitter, the tone signal either being controlled by the clock switch or being of a frequency characteristic of the repeater in which it originates. The indicating arrangements at a terminal station comprise red, green and amber lamps for each repeater. The green lamp indicates the reception of indicating pulses, the amber lamp their non- reception and the red lamp the reception of the emergency tone, Thus three different conditions of a repeater are reported. (A) Twoway traffic is going through the repeater, indicating pulses being inserted in channel 1 of the north-bound and south-bound pulse trains ; (B) Traffic is interrupted in one direction, e.g. south-bound. The indicating pulses are missing from the north-bound pulse train and the emergency tone is received by the south terminal. (C) A repeater is completely shut down, the repeaters adjacent thereto each generating emergency signals for transmission in both directions. The arrangements for transmitting the indicating pulses and emergency tone in the northward direction at one repeater station are shown in Fig. 4. The north-bound pulse train picked up on aerial 19 and receiver 17 is passed through amplifier 81 to the northward transmitter. In a parallel path, the marker pulses are separated and delayed in circuits 77, 78, modulated if desired in circuit 48 and shaped at 50. They are then normally passed through the follower valve 52 to the same transmitter to form the indicating signals when the clockoperated switch 60 energizes relay 61 to apply anode potential to valve 52. Relay 61 can only be energized when valve 59 is rendered conducting by radiation from the southward transmitting aerial 15 picked up on an adjacent dipole 21, rectified and amplified in circuits 56, 58 and applied to valve 59. If this transmission fails the indicating pulses are inhibited by the de-energization of relay 61 and the breaking of the anode circuit of valve 52. When no signals appear at the output of receiver 17, the prohibitive bias, produced by rectifier 66, on the grid of valve 67, ceases and relay 65 is energized. This also breaks the anode circuit of valve 52 and energizes the emergency tone generator and amplifier 79, 80 to modulate the northward transmitter. If the switch 72 is in its lower position production of the emergency tone is also controlled by the clock switch 60. The terminal faultindicating equipment is shown in Fig. 2a. The pulse train at the output of the receiver 4, 3, 83, is passed to the channel distributer 84, the indicating pulses in channel 1 being fed through amplifier 86 to close a path to earth in circuit 87 from the moving contact of a rotary distributer 89 controlled by clock 91. The clock ensures that the indicating pulses control lamps associated with the repeater from which they originate. For this purpose, relays 92, 93, 94 are normally energized thereby to light the green lamps on panel 96. If the pulses are not received the appropriate relay is de-energized to light the associated amber lamp. Where the emergency tone signals are of different frequencies for the several repeaters, filters 97, 98, 99 select the individual frequencies which control relays 104, 105, 106, respectively to light the red lamps. These relays have additional contacts which, should one relay be operated, the current supply to all the green and amber lamps is interrupted. When all repeaters use the same emergency tone, at clock controlled intervals, the red lamp relays are also controlled by the clock at the terminal equipment and only one tone filter is necessary, Fig. 2b (not shown).