Transistor radio tuning indicator - use double amplification of tapped detector voltage to illuminate light emitting diodes

摘要

The transistor radio tuning indicator uses light emitting diodes. The illumination of these diodes is controlled by a circuit which double amplifies the continuous voltage tapped from the detector stage (C). The first stage of amplification consists of filtering (F1) the detection voltage. This voltage is then applied to the base of the first transistor (T1) of the receiver. The voltage appearing at the emitter resistance is then passed on to the second stage amplifier via a filter (F2). The second stage of amplification (T3) uses a low power NPN transistor. This transistor produces a voltage at its collector which can be adjusted by a resistance (R2, R3, R4). The collector voltage is used to illuminate the LED's (D1, D2, D3).