GB289050A - An arrangement for the automatic control of the efficiency of transmitting systems, particularly for high frequency transmitting systems - Google Patents

Abstract

289,050. Siemens & Halske Akt.- Ges. April 21, 1927, [Convention date]. Duplex signalling; fading, preventing; automatic gain control. - Relates to means for preventing " singing " between the outgoing and incoming lines of a duplex circuit, where, as in a combined wired and wireless system, a part of the circuit has a fluctuating conductivity (due to fading effects). According to the invention provision is made to ensure that the circuit as a whole has a minimum overall attenuation bv utilizing a control current the frequency of which lies outside the normal range of signalling frequencies, and by applying such control current to regulate the overall amplification factor at a point along the transmission line which precedes the entry of the combined control and signalling currents on to the regulating apparatus, so that alteration of the amplification ratio influences both currents simultaneously. As shown in Fig. 2, a special control frequency, lying outside the normal speech frequencies, is imposed by a generator O upon the outgoing radiation. In the receiving circuit, this control frequency is diverted by filters S2, S3 into a branch relay R, where it controls a motor M which automatically adjusts the setting of a potentiometer P so as to ensure that the strength of the received signals is maintained below the point at which a regenerative action would occur. A constructional form of relay is shown in Fig. 3. If the signal voltage grows too strong, the relay R2 is closed, the relay R3 is simultaneously opened, and an electromagnetic clutch on the wheel V reverses the previous direction of the shaft T, which carries the adjustable tapping to the potentiometer P, Fig. 2. For weaker signals the relay R1 connects the differential wheel W to the driving motor M, so that the potentiometer setting fluctuates about a mean point determined by the sensitivity of the relay R2. In the alternative arrangement, the same effect is secured by using only one relay. The generator O, Fig. 2, can be used directly to calibrate the sensitivity of the receiving relay.