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DIY Transistor Radio

Do-it-yourself (DIY) transistor radios have become tools used by educators and experimenters. In the 1950s, Knight and Heath had kits that were popular. Japan and the Orient entered the market with micro radios. Today, radios are everywhere in every form for every pocketbook. Transistors in microchip circuits have replaced many electronic systems in military and satellite communications and computers. Even Ham radio equipment has followed the avenue of the microchip. One no longer repairs a chip. You simply replace it. DIY transistor radios are made for the student to learn and the enthusiast to enjoy.

Two Transistor 'Mini-Radio' on a PCB
- This project is called the "mini-radio" because it uses few components and is easily constructed. A schematic is provided with a printed circuit board (PCB) layout along with a parts placement view of the PCB. Board construction is not covered here. You can do it with a kit or parts from a local electronics supply house along with other needed components. T1 functions as a feedback-regulated, high-frequency amplifier and acts as a demodulator at the same time. Sensitivity is controlled by how much feedback is received from P1, the 1k potentiometer. The demodulated signal comes from T1's collector and is filtered by C3 so that the only signal amplified in T2 is the audio. This signal then drives the high-impedance earphone. Some construction is involved with wrapping 65 turns of AM wire around a 10cm-long-by-10mm-diameter ferrite rod. Place the tap at turn five of the coil, counting from the ground end. Install this coil as close as possible to the PCB.
  
  The radio will operate with or without an external antenna. An external antenna, however, will greatly improve sensitivity. Attach the external antenna to the hot end of the coil, away from the ground side, through a 4.7 picofarad capacitor. A nine-volt battery is fine for power because it uses only one milliampere (mA).
  
  This is a good DIY project because it gives experience in PCB construction and the lost art of coil winding.
  
  Finally, the most challenging task is to enclose it in a case that is both functional and original.

Ham Radio