Wideband Rf Signal Tracer

EE JULY/AUGUST 1988 This simple and versatile circuit can aid in troubleshooting defective RF ampli- fier circuits. The usable frequency range of the tracer is about 100 kHz to 30 MHz. Measured signals (0.5 mV to 500 mV) are amplified, detected and made audible with the aid of a small loudspeaker. MOSFET Ti functions as an amplifier with a high input impedance to avoid loading the signal source. Transistors Tz, T3 and T4 form a high-gain logarithmic amplifier that drives AM demodulator Ts-Ds. A single chip AF power amplifier, ICI, is included to make detected signals audible. Testing of RF equipment is carried out simply by "probing around" at suitable lo- cations in the circuit and listening to the detected signal, whose relative ampli- tude can provide an indication of poss- ible sources of malfunction. The tracer"s logarithmic amplifier obviates the need for frequent re-adjustment of the volume control, Pi. The unit is so sensitive that it produces audible output when the in- p...