Center tap of T1 (any small AF transformer) can be grounded. CR1 and CR2 are germanium diodes. Noise figure with optimum source resistance is about 3 dB at 150 MHz. Am- plifier is capacitively coupled common-emitter cascade. Pure sine-wave signal is applied to device under test, and out- put of device is fed to AF input of distortion meter. With S 1 normally open and S 2 normally closed, circuit operation is normal. If switch positions are simultane- ously reversed, response remains flat regard- less of positions of bass and treble pots, center- frequency gain remains unchanged, and phase shift is unchanged. Ori- entation of symbols is unimportant; artists choose the position that is most convenient for making connec- tions to other parts of the circuit. Uses 12-VDC 1000-ohm 1-A relays, Tl SN7274IL opamp U1, and wirewound 360° ro- tation command pot R7 operating from 14-V regulated supply of original control.
Signal wires are twisted together in shield acting as ground. Ranges are 0-1 and 0-10 W. L 2 is T-50-2 toroid wound almost full with No. 28 enamel, leaving only room for 2-turn link L,. C, and C 2 are 3-20 pF trimmers. Entire circuit must be duplicated for other stereo channel. Meter rectifier bridge is in feedback loop of opamp, to give highly linear AC/DC con- version with flat frequency/amplitude response and short voltage rise time at low cost. The longer the reference antenna used, the greater will be the sensitivity of the meter.
Ferrite 4ecring is 0.5-inch Mullard FX1596 or equiva- lent. — P. G. Martin, Some Directional Wattme- ters and a Novel SWR Meter, 73 Magazine. For other IF, such as 10.7 or 11.7 MHz, capacitor values should be changed accordingly. Hundreds of cross-references in the index aid searching.