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AF/RF
Signal Tracer
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| Signal
tracer is a very impo- rtant test gear in almost all phases
of electronics troubleshooting. Described here is a compact,
simple to construct and inexpensive circuit capable of
tracing the presence of audio frequency (AF) as well as
radio frequency (RF) signals. The circuit basically consists
of an audio amplifier and a loud-speaker with a switched
input network for AF and RF signals. The whole gadget
can be made small enough to be enclosed inside a metallic
cabinet for convenience. Audio amplifier section of this
circuit is built around IC TDA 2822M, which is a low power
stereo amplifier in 8-pin mini DIP package. Here the IC
is used in bridge configuration to increase the output
power to about 250 mW, which is fed into a 4-ohm, 500
mW rated loud-speaker. The idling current of the circuit
is less than 10 mA with 3V battery. The audio volume is
loud enough to serve the intended purpose. When selector
switch S1 is in AF position, the audio signals are applied
to the input of the AF amplifier (pin 7 of IC1) via capacitor
C2 and potentiometer VR1. Capacitor C2 also isolates the
input of amplifier from DC voltage present in the audio
frequency signals. The input signal level of IC1 can be
adjusted with the help of potentiometer VR1. When the
selector switch is in RF position, the detector and demodulator
circuit—formed by capacitor C1, diode D1, and resistors
R1 and R2—is connected at the input of the circuit.
Detected audio signals are then fed to the actual input
point of the audio circuit for amplification as explained
earlier. |
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