GB914434A - Improvements in or relating to radio transmitter - Google Patents

Abstract

914,434. Automatic control systems. STANDARD TELEPHONES & CABLES Ltd. Sept. 11, 1959, No. 31041/59. Class 38 (4). Power is supplied from a radio frequency source through an adjustable coupling element to a variable impedance and signals proportional to the square root of the power supplied to the load and proportional to the voltage of the radio frequency source are opposed to control the coupling element to reduce variations of power with variations of load impedance. In Fig. 1 the tank circuit 6 of the final stage of a radio transmitter is maintained in resonance with the signal applied at 2 from the preceding stages (not shown), by a reversible motor 12 automatically adjusting an inductance 11 under the control of a phase discriminator 16. Tank circuit 6 is coupled to an aerial 10 through another adjustable inductance 7 and a coaxial line 9. A circuit involving a current transformer T, a potential divider 37, 38, and rectifiers 31, 32, derives a voltage E2 proportional to the square root of the power supplied to the aerial. A circuit including a potential divider 23, 24 and a rectifier 22 derives a voltage E 1 proportional to the output voltage of stage 1. Any difference between voltages E 1 , E 2 is effective through a relay 17 to run a motor 15 and thereby adjust inductance 7 in the appropriate direction to prevent variations of aerial power, e.g. due to icing. Simpler circuits for deriving a less accurate approximations to the square root of aerial power are described.