Solar Powered Radio
This project allows you to study a simple one Transistor radio powered by the Solar Cell. Experiment with different Antenna and Ground connections until you find a combination which works well. Remember, some Antennas give best response when no Ground connection is used.
The tank circuit is made up of the Antenna coil and Tuning Capacitor in parallel. This circuit gives selectivity. That is, it allows you to separate the stations from each another. Of course, a single tuned circuit like this cannot give as much selectivity as we would really like.
The Diode detects the signal by rectifying the RF voltage. This allows the audio variations in the amplitude of the signal to be recovered.
The 0.02uF Capacitor is called the detector output filter. It smoothes out the rectified RF voltage so that the resulting voltage is only the audio signal variations and an average level of voltage (DC) which is dependent on RF signal strength.
The Transistor uses the DC voltage from the detector and filter as base-bias. This turns the Transistor ON and allows the signal to be amplified. Notice that because the detected signal is used to turn the Transistor ON, the Transistor is OFF without a signal, and ON harder for strong signals than for weak signals.
The Solar Cell converts light energy directly into electrical energy. This is used as the collector bias voltage and current. The Transformer winding is used to present a low resistance to this DC bias while presenting a very high impedance across which the audio output signal can be developed.
The Earphone changes the amplified (but weak) audio signal into sound.