| 摘要 |
725,947. Automatic volume control. AUTOMATIC ELECTRIC LABORATORIES, Inc. Jan. 28, 1953 [Feb. 4, 1952], No. 2466/53. Class 40 (4). A pilot-controlled gain regulating device for a line transmission system comprises a bridge circuit including a variable impedance element and a frequency-selective network in one arm thereof, wherein the input is applied across one diagonal and the output, which includes a second variable impedance element, is taken from across the other. The arrangement, which is designed to correct for the difference in the rate of change of transmission constants with frequency for different weather conditions, compensates for over attenuation of lower frequencies by equaliser 3, Fig. 1, during dry conditions. The bridge comprises the two halves of secondary winding 7 of the hybrid transformer, a resistor 9 of approximately 300# and a circuit including a tungsten filament lamp 17 shunted by a 300# resistor 19 and a large blocking condenser 20, and a tuned network comprising condensers 23, 27 and resistors 25, 29. The pilot frequency which is at the upper end of the band is selected by a filter 45, rectified in a rectifier 49 and applied to the grid of a valve 55 to control the current in its anode circuit which includes the variable resistance lamps 17 and 43. The network which is tuned to the higher frequencies reduces the level of high frequencies at dry conditions and lamp 43 which is shunted across the line effects gain control. Alternative types of variable impedance element may be used in which the resistive changes are +ve orve and the bridge would be modified accordingly. |
