GB526726A - Improved attenuator for modulated-carrier signal receivers - Google Patents

Abstract

526,726. Wireless receiving systems. HAZELTINE CORPORATION. March 25, 1939, No. 9428. Convention date, April 7, 1938. [Class 40 (v)] An attenuator for use in a modulated carrier receiver comprises one coupling path producing voltage at the input of an amplifier and a second coupling path, whose gain is controlled in accordance with signal strength, which injects a voltage into the cathode circuit of the amplifier in opposed phase. Signals from the antenna 10 are passed by the tuned circuit 20, 21, to the radio frequency amplifier 13 and then on to the normal superheterodyne receiver 14 - 18. An extension 40 of inductance 20 together with condenser 41 provides neutralization of undesirable capacitive coupling through valve 13. The cathode resistance 24 is not byepassed for high frequencies but the anode circuit is returned direct to the cathode for high frequencies by condenser 27. The second coupling circuit consists of valve 25 whose grid circuit is connected across the tuned input circuit and whose load circuit consists of resistance 24 which is common to the cathode circuits of both valves, resulting in a signal voltage of opposing phase being produced in the cathode grid circuit of valve 13. In order to provide control biases for valves 25 and 13, signals from the input circuit are amplified in valve 28 and passed to diode rectifier 29. The voltage generated across load resistance 32 is applied positively over filter 34, 35, to' increase the amplification of valve 25 as the signal input increases. Simultaneously an auxiliary diode 37 in valve 28 produces a voltage which is applied negatively to reduce the gain of valve 13. The circuits following valve 13 are more selective than circuit 20, 21, so that undesired as well as desired signals are included in the input to amplifier 28. A filter, or other circuit having a resistive impedance over the band of frequencies for which the circuit is to operate, can be utilised in place of resistance 24. In a modification, Fig. 2 (not shown) the amplifier 28 is dispensed with, the bias for the valve 25 being obtained from a diode coupled to its own output, while the control bias for the valve 13 is obtained from the normal A.V.C. supply in the superheterodyne receiver. In another modification, Fig. 3 (not shown), the auxiliary valve 25. is dispensed with. The cathode resistance is provided and the screen circuit of valve 13 is not decoupled for radio frequencies. An amplifier fed from the input circuit feeds a diode which developes a controlling voltage which is fed negatively to the suppressor grid of valve 13. As this bias increases negatively it causes the amplification. of valve 13 to decrease and also due to the increased screen current causes a degenerative signal to be developed across the cathode resistance. Specification 526,725 is referred to.