Wireless Code Transmitter
This project is a simple but effective code transmitter as used by the military and by amateur radio operators around the world. Code is sent with the key which turns the transmitter ON and OFF in the required sequence.
The Morse Code (which has been accepted as the universal code language). A common AM radio may be used to receive the code sent out by this transmitter, if the radio is first tuned to a weak station. This transmitter signal then mixes with the station's signal to produce an audio tone which is called a "beat note".
It is this beat note which is then heard as the code signal. Tune this transmitter (using the Tuning Capacitor) until a desired and strong beat note is heard in the receiver when the key is pressed. The continuous wave (CW) signal of this transmitter may also be received on a communications receiver without having to tune to another station, if the communications received has a "beat frequency oscillator" (BFO).
The BFO beats with the CW signal from this transmitter and produces the tone. The two requirements for an oscillator (gain greater than 1, and regenerative feedback) are provided by the Transistor (gain) and tank circuit connections. The emitter is connected by the 0.1 uF Capacitor to the center-tap of the ferrite coil. The collector is directly connected to the top end of the tank circuit (out-of-phase connection).
The 100K Resistor provides some base-bias current to turn the Transistor OFF as required for operation as an amplifier or oscillator. Transmission and reception of CW signals is very efficient (much more so than voice modulation of any kind) so that during times of emergency this is the most reliable type of transmission.
You may find that because of this high efficiency, no antenna is required, or if one is needed, only two or three feet (about 60 - 90 cm) of wire will do. Have fun!