GB567352A - Carrier wave circuit protection - Google Patents

Abstract

567,352. Wireless transmitting systems. STANDARD TELEPHONES & CABLES, Ltd. Aug. 27, 1943, No. 13995. Convention date, June 23, 1942. [Class 40 (v)] [Also in Group XXXVII] In a radio transmitter, protection is afforded against lightning discharge or other abnormal condition by balancing rectified carrier output voltage against a voltage derived from the supply source of the transmitter, want of balance being utilized to interrupt the carrier excitation and to disconnect the source of modulating signal. The carrier generator 1 is connected through a control amplifier 2 and intermediate amplifier 3 to the Class C power amplifier and modulator stage 4, from the tuned anode circuit of which the modulated carrier passes by a transmission line 26 to the circuit of the aerial 6. The output carrier is also shunted through a blocking-condenser 27 and coil 28 to a rectifier 29 giving a direct current through a resistance 32, meter 40 and relay coil 41. The supply source 7 for the anode voltage of the power amplifier is connected thereto through a regulator 8 and rectifier 9, and is also connected through a transformer 34 and voltage divider 35 to a rectifier 36 which gives a direct current through resistance 33, meter 40, and relay 41. Normally, these two direct currents balance and the relay 41 is unenergized ; but if an arc or short circuit occurs between the aerial and earth, the relay 41 pulls up, energizes a slow-release relay 43 and shorts itself at the contact 50. Contact 46 opens and permits battery 48 to apply prohibitive bias to the amplifier 49 ; and contact 51 closes to short-circuit the modulating-source 12, this source being normally connected through amplifiers 13, 14 to a transformer 11 in the anode supply lead of the amplifier 4. The smoothing - condenser 37 eliminates pulsations at the supply frequency, and the condenser 30 eliminates pulsations at the carrier frequency and at the modulating frequency, so that the circuit balance is not affected by the modulation of the carrier. In a modification, Fig. 2 (not shown), the rectifier 36 and transformer 34 are omitted, the direct current through the resistance 33 being supplied through a high resistance and potential divider connected between the anode supply lead 10 and earth.