Patent GB-808461-A (GB)
Title: Improvements in or relating to radio telegraph systems
Inventor: HOLLAND JOHN DOUGLAS
IPC: H04L1/20
Filed: 1957-03-04
Abstract: 808,461. Code telegraphy. STANDARD TELEPHONES & CABLES Ltd. March 4, 1957, No. 7077/57. Class 40 (3). A telegraph receiver for operation in response to a telegraph wave representing alternations of marking and spacing signals comprises-means for effectively measuring the rate at which signals, as represented by the corresponding voltage transitions are being received, and means for performing a switching operation when the measured rate reaches a predetermined limiting value. The signals are defined by the transitions of the signal wave, the transition from spacing to marking potential being defined as a marking signal, and the transition from marking to spacing potential defining a spacing signal. The incoming double-current signals at terminals 1, 2 are applied via the shaper amplifier 3 and contact 8 to the teleprinter 4 and also to the grid of a valve 13 of a trigger pair 13, 14. A positive (marking) pulse at terminals 1, 2 makes valve 13 conductive and valve 14 non- conductive to pass a pulse via capacitor 22 and rectifier 24 to an integrating circuit 25, 26. In response to spacing (negative) pulses, the valve 14 becomes conductive and the negative pulses at the anode resistor 17 are shunted via rectifier 27 to ground. The voltage from the circuit 25, 26 is passed to the grid of the valve 29 of a trigger-pair 29, 30 and normally the valve 29 is non-conductive and the valve 30 conductive so that the relay 7(A) is energized. If the number of marking signals in a predetermined period, e.g. 60 seconds, exceeds a predetermined rate per second, e.g. 15, by suitable choice of the time constant of the elements 25, 26, the voltage applied to the grid of the valve 29 rises above a preset level determined by adjustable potentiometer 35 to render valve 29 conductive so that valve 30 is cut off and releases relay 7(A), moving contact a<SP>1</SP> to connect battery 9 to the teleprinter 4 to hold it in the stop condition and at released contact 10, a<SP>2</SP> closing the circuit of an alarm lamp 11. The arrangement may be modified to operate in response to the number of spacing pulses in a fixed time interval, or may be adapted to be operable by single-current signals. In the application of the control circuit of Fig. 1 to a frequency diversity system, indicated by Fig. 3, the signals received over the respective channels 50, 51 are applied over operated contacts 56, 57 of respective relays 54, 55 to the shaper amplifier 3 and the teleprinter 4. In the case of disturbance on one of the channels 50, 51. operating one of the circuits 52, 53 to release its respective relay 54, 55, the signals pass to the conductor 59 over the other channel, and one of the contacts 60, 61 is closed without effect, but the occurrence of disturbance on both channels with the release of relays 54, 55 disconnects the input from conductor 59, and the closure of released contacts 60 and 61 connects battery 9 to the teleprinter 4 to hold it in the stop condition until one or both of the channels 50, 51 is/are free from interference. The system, shown in Fig. 3, may be employed for reception on three or more channels by connecting at 62 one or more control circuits, such as 52 or 53.