Elenco Electronic Playground 50-in-1 Experiments - Manual (Page 59)

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The circuit you have just built as an AM radio transmitter
also has other applications. There is no schematic or
Wiring Checklist here because we are using the same
circuit.
Can you think of a way to use this circuit as an AM radio
jammer? Here’s how. Place your AM radio next to your
Electronic Playground and tune it to a local AM radio
station that is close in frequency to where the last
experiment operated (at the low end of the radio’s tuning
range). Now adjust the variable capacitor to place your
AM transmitter on the same frequency. When you’ve
done this you will hear a hum or no sound at all instead
of the radio station. If you can’t get this to work then you
probably picked a radio frequency that your AM
transmitter can’t reach, as we discussed in the last
experiment. Pick a different radio station and try again.
So now you have an AM radio jammer. This works
because is the signal from your transmitter is stronger
than the signal from the local radio station and “drowns it
out” the same way someone standing next to you yelling
makes it hard to hear somebody else talking to you softly.
You can test the range of your jammer by moving your
Playground away from the radio until you can hear the
radio station again. And note that your jammer range
depends on which radio station you listen to, since some
stations will be stronger than others. You don’t need to
talk into the speaker to jam because your transmission
itself does the jamming, not what you say. If the jammed
radio station is weak enough then you may be able to talk
into the speaker and be heard on the radio as if you had
taken control of the radio station.
Can you think of a way to use this circuit as a metal
detector? Here’s how. Keep your Playground and AM
radio set up so that you are jamming a local radio station.
Now take a solid metal object, such as a magnet, and
bring it close to your Playground antenna. You should
hear the radio station again, this is your indicator that you
have detected metal. Do you know how this works? Your
metal object changes the antenna’s inductance by
changing the magnetic field around the iron bar through
the antenna, just as wrapping the antenna coil around the
iron bar increased the antenna inductance. By bringing
the metal object close to the antenna you change the
oscillator frequency (since the inductance changed). So
your jammer is still working but its not jamming the
frequency that your radio is tuned to, so you hear the
radio station. Now you can hunt for buried treasure!
EXPERIMENT #40: Radio Jammer / Metal Detector
Wiring Checklist:
o 25-to-26-to-47-to-45-
to-41-to-39-to-33-to-35
o 28-to-9-to-16
o 17-to-38
o 7-to-30-to-29
o 15-to-31-to-44-to-48
o 8-to-32-to-42-to-19
o 20-to-40-to-34
o 18-to-51-to-46-to-36
o 37-to-23
o 5-to-21
o 6-to-22
o 43-to-52-to-50-to-27