Show Volume-Control Means for Radio Receivers Experimenters who have attempted to adapt some of the volume-control methods used in D. C. receivers to A. C. sets have found that it was possible possi-ble to get a good mimimum or low volume point. This trouble occurs when the volume control is used in the circuit of a radio-frequency tube ahead of the detector. This control usually consists of o variable resistance shunted shunt-ed across one of the tuned circuits. The reason for Inability to reduce the signal to "zero" is that the power line Is acting as a line of the carrier-current carrier-current type (acting as the line does in "wired" wireless) and bringing the high-frequency signal Into the set through the plate-supply unit There may be sufficient signal Impressed on the detector to give good reproduction even when the volume control is set for no signal. To overcome this it Is necessary to offer a very high impedance to the radio-frequency currents to "choke" them out. A radio-frequency choke should be Inserted in the radio-fre queney plate-supply lead at the receiver. re-ceiver. A .01 or .02 mica condenser should then be connected from the receiver re-ceiver side of the choke to the grid return lead (potentiometer mid-tap). |