Elenco 130-in-1 Electronics Playground - Manual (Page 131)

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This circuit is a simplified but effective code transmitter
similar the kind used by military and amateur radio
operators around the world. As the key is pressed and
released, the transmitter turns on and off in sequence.
The code send out by the transmitter can be received
using an AM radio. The radio should be tuned to a
weak station. When the transmitter signal mixes with
the station’s signal it produce an audio tone, called a
beat note. The code signal transmitted is the beat note
you hear on the radio. Use the tuning capacitor to
tune this transmitter until you can hear the beat note
in the radio when you press the key.
If your communications receiver has a beat frequency
oscillator (BFO), you can receive the carrier wave
(CW) signal of this transmitter on a communications
receiver, without tuning to another station,. The BFO
beats with your transmitter’s CW signal and produces
the tone.
The frequency of this oscillator sends out an RF signal
because is very high (500,000Hz to 1,600,000Hz).
Tuning to a weak AM station first, then sending a
signal slightly off from the station frequency, you can
hear the beat note that you produced.
This type of transmission and reception of CW signals
is very efficient and most reliable type of transmission
for some emergencies. You might find that you do not
need an antenna or only 1- 3 feet (about 60-90 cm) of
wire.
Notes:
EXPERIMENT #110: AM CODE TRANSMITTER
Schematic
Wiring Sequence:
41-6-11-ANT
7-89-110-137
8-12-100
40-90-99
42-79
80-109-119
121-122
124-138