Patent GB-717083-A (GB)
Title: Improvements in and relating to the automatic monitoring of telecommunications apparatus
Inventor: PEACHEY FRANCIS ARTHUR
IPC: H03F1/54
Filed: 1952-06-19
Abstract: 717,083. Monitoring transmitters. BRITISH BROADCASTING CORPORATION. June 19, 1953 [June 19, 1952], No. 15479/52. Class 40 (5)] For monitoring the transmission of signals through communications apparatus, an indicator, alarm or switch is responsive to a predetermined difference between the output of two rectifiers connected to different points in the apparatus and responsive to excursions of the signal voltage at these points into a range of values having a lower limit other than zero. In the embodiment described, the apparatus is a radio telephony transmitter and at the two points occur the modulating signal and the rectified output of the transmitter, respectively. The audio modulating signal is applied through transformer 10, Fig. 1, and a network 11, 12, 13, for attenuating the upper and lower frequency ranges, to a full wave rectifier 14, the D.C. output voltage of which is applied to a condenser 15 when it exceeds the biasing voltage of the rectifier 16 provided by source 17. A rectifier 20; biased by source 21, is shunted across the condenser 15 to determine the upper limit of the condenser voltage. Across the condenser is also connected one winding 18 of a differential relay 18 and a resistance 19 which determines the discharge time. The rectified transmitter output is applied to transformer 25, feeding rectifier 29 through network 26, 27, 28 and the other winding 31<SP>1</SP> of the differential relay is fed from condenser 30 limiting rectifiers- 31, 33 being biased by the sources 17, 21 respectively. It can be arranged that fluctuations in the mains suply voltage to the transmitter do not cause the relay to operate, by replacing the sources 17, 21 by resistors across which potentials derived from the rectified mains supply are maintained. It is shown that the circuit responds to a reduction of modulating or carrier amplitudes but not to excessive modulating amplitude. The transmitter may be switched out of circuit or a faulty section replaced by operation of the relay. For switching out the transmitter should it become unduly noisy a further circuit may be provided fed from the same two points through networks 37, 38, 39, Fig. 3, and 45, 46, 47 and transformers 40, 48 respectively. The full-wave rectifiers 41, 42 and 49, 50 have their load circuits 43, 44 and 51, 52 connected to the grids of valves 53, 54 respectively, the anode currents of which pass through the windings of a differential relay 55. Normally 'both valves are cut off but when the signal voltages become low the valves conduct and any difference of signal voltage operates the relay. To avoid switching off the transmitter due to a fault in this circuit, the relay 55 may be arranged first to apply test inputs to the circuit and also to operate a second relay which will disconnect the transmitter after a time delay. If the test results in a re-operation of relay 55 the second relay is released and an indicator is operated to show that the circuit is faulty. A similar arrangement may be used with the main monitor circuit of Fig. 1.