The tracer receiver is a stereo audio amplifier/detector circuit operating near 1 kHz. Inductors Ll and 12-hand-wound coils, consisting of 200 turns of #26 wire on 2-inch ferrite cores-are tunea to the operating frequency of the amplifier/detector. The received signal strength of each individual receiver is indicated by an LED. The audio output of the receiver is fed to a stereo headphone. That dual-receiver scheme helps in locating and tracking the hidden wire or cable by giving a directional output that indicates the cable`s path.
Tracer-receiver - schematic

The 1-kHz signal is picked up by Ll and coupled to the input of op amp Ula, which provides a gain of about 100 dB. The output of op amp Ula is fed through volume-control potentiometer R7 to the input of Ulb, which magnifies the already amplified :;ignallOO times more. That puts the maximum gain of the receiver at about 10,000 dB. The output of Ulb follows two paths: in the first path, the signal is couple through C9 and Rl3 to Jl, and is used to drive one half of a stereo headphone. In the other path, the signal is fed through a voltage doubling/detector circuit-consisting of Dl, D2, Cll, and Cl3-that converts the amplified 1-kHz signal to the de voltage that"s used to drive Ql. When Ql is turned on, LEDllights, indicating a received signal.

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