TRF AM Radio Receiver
In this project I built a simple two transistor Tuned Radio Frequency AM Radio Receiver powered from a single 1.5V AA battery. A tuned radio frequency receiver (TRF receiver) is a radio receiver that is usually composed of several tuned radio frequency amplifiers followed by circuits to detect and amplify the audio signal. Here is the schematic. This radio doesn’t have great selectivity or sensitivity, which are common disadvantages that TRF’s are known to have. Selectivity requires narrow bandwidth, and narrow bandwidth at a high radio frequency implies high Q or many filter sections. There is only one tunable filter section in this radio and the Q of this tunable tank circuit isn’t extremely high. This radio gets around eight stations loud and clear.
This was the first radio receiver that I ever built and getting it to work was a learning process. At first I tried to wire it up with a dead bug construction. After wiring it up this way the radio started to oscillate and it wouldn’t pick up any stations. I decided to scrap this approach, not so much for the fact that the radio was oscillating, but more because it was too ugly for my liking. To circumvent this dilemma I decided to buy some FR-4 perfboard, which helped organize the components and gives a more clean look.