Posted on Apr 18, 2012 10420
The AM Tuned Radio Frequency (TRF) receiver, has a sensitivity of about 1 m V at tbe input for an audio output of `iz W. Capacitor C22 couples audio signals from the power line to the PC board-it must be rated at 600 Vdc. R8 will cause F1 to blow, if C22 shorts. The signal from C22 goes to a tuned network (C1 through C5, Ll, and L2) that has a 20-kHz bandwidth, which allows only the desired signal to pass through. IC1 is a gain block i-f chip that has AGC capability and approximately 60 dB of gain. Components C8, C9, and L3, which are placed across tbe output of IC1, are broadly resonant around 280kHz.
C10 couples rf to detector -diode D 1, which is used as an envelope detector. The detector output is taken from C14, which sets the upper frequency limit at about 10kHz or so. By reducing tbe value of C14, high frequency response can be obtained. The detector output is connected to an external jack. Audio components are fed to audio-gain control R6, through C16 to IC2, an audio amplifier. C18 couples up to 1/z watt of audio to an external speaker. The kit is available from North Country Radio, P.O. Box 53, Wykagyl Station, NY 10804.