Elenco 130-in-1 Electronics Playground - Manual (Page 140)

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This experiment is a wide band, untuned RF signal
tracer. You can use it to check for antenna signals
and find sources of RF noise and interference. This
circuit is like an untuned crystal set.
The 100pF capacitor in the input blocks DC and the
60Hz power line frequency, so the wires can touch
almost anywhere without fear of electrical shock. Of
course, you should never intentionally probe around
high voltage.
Attach the probes between grounded objects and
other metallic objects that can act as antennas. You
will find that this circuit allows you to receive all kinds
of AM signals as well as noise. For example, if you
have citizens’ band transmitters, you can hear these
signals if the transmitter is close enough to the signal
tracer.
Sometimes you might hear noise from fluorescent
lights, auto ignition systems, light dimmers, or
switches opening and closing.
Notes:
EXPERIMENT #118: RF SIGNAL TRACER
Schematic
Wiring Sequence:
89-97-126
90-92-100-EARPHONE-PROBES
125-99-91-EARPHONE
98-PROBES