AM Radio Station 2
You have built AM radio transmitters in earlier projects, but they have been used to send only a single tone or series of dots and dashes.
With the AM RADIO STATION you will actually send your voice through the air. The Speaker acts as a dynamic microphone in this circuit, and you will notice that the Transformer marked OPT (output) on the Schematic and 'bread board' is actually being used as an input transformer (this has been done in many of the projects).
When you finish the wiring, turn on your AM radio receiver and tune it to a weak station or silent setting on the dial.
Now begin to talk into the Speaker while adjusting the Tuning Capacitor, until you hear your voice "on the air".
This transmitter may only send signals a few feet, so the AM radio will have to be close by. This transmitter works very much like the one in the Light Operated Wireless Burglar Alarm in radio section except that the audio frequency (AF) oscillations provided electronically in project Wireless Burglar Alarm, are created by your voice and the Speaker (microphone) in this circuit.
The 2SA(1) Transistor amplifies the AF signal and this signal modulates the amplitude (strength) of the signal being produced by the RF (radio frequency) oscillator.
The RF is tuned to the setting on your AM radio dial by the Tuning Capacitor and Antenna Coil (remember this is called a 'tank circuit') and sent out through the Antenna.
The 2SA(2) Transistor helps in controlling the amplitude of the RF signal, also. The 2SC Transistor is a part of the RF oscillator and provides the primary amplification of the RF signal (before the AF signal modulates it). If you ever wanted to be a 'DJ', now is your chance.