GB334869A - Improvements in transmission volume control systems for electric signalling - Google Patents

Abstract

334,869. Electrical Research Products, Inc., (Assignees of Mitchell, D., and Silent, H. C.). Dec. 17, 1928, [Convention date]. Automatic gain control. - In an automatic volume control system for radio telephony or for long submarine telephone cables, means are provided to prevent hunting when the energy level is constant, and in a two-way system for holding the transmitting channel automatic volume control means constant while the receiving channel is operative. Fig. 1 shows a one-way channel L2' L, and amplifier 3 and a volume control potentiometer PI operated by control apparatus 4. The volume control apparatus may comprise motor or relay operated devices or thermionic valve arrangements controlling grid biases or impedances. An amplifier-detector 2 bridged across the input is arranged to operate a weak volume relay A while the output amplifierdetector 1 operates a high volume relay E, and a correct volume relay B, which control relays C, D, associated with the control apparatus 4. Relay C is slow to release and relay,D slow to operate so that increase of the signal volume is only effected if relay E is maintained energized. At the conclusion of conversation the relays return to normal without affecting the potentiometer setting, i.e., the system is " full neutral." Fig. 3 shows a system normally set for maximum gain by omission of the minimum input relay A so that in the absence of signals the potentiometer P1 returns to maximum setting. Relay 20 is operated from the receiving channel and by energizing relay G prevents the operation of the control apparatus 4 while the receiving channel is operative. The control apparatus 4 in addition preferably is extended to control the gain in the receiving channel in the opposite sense to the control effected. in the transmitting channel to prevent singing or echo. In a modification (Fig. 2, not shown), provision is made in the absence of signals to return the potentiometer to a setting to give any required normal gain. Fig. 5 shows a semi-neutral system which returns to an increased gain setting after the loudest speaker, but is neutral after all other speakers. Contacts S1, S0 normally close the increase and decrease gain circuits respectively when the relays are normal and thus return the control apparatus 4 to a normal setting while contact S, operates relay F to decrease the sensitivity of the input amplifier-detector 2. Return to minimum by contact So during pauses is prevented by slow release relay H.