Signal Injector Circuit


A signal injector is a very useful and quick troubleshooting tool for signal tracing in a circuit. Using it can quickly determine the faulty stage of a radio receiver, for example. The signal injector can be applied to the speaker output, and if you hear the signal you can move to the preceding stage of the circuit. In this case an audio amplifier, and if you again hear the injected signal, you move the signal injection up the stages of the circuit until you no longer hear it, potentially letting you know where the problem lies.

http://www.partsim.com/simulator#12726

Signal Injector

RefDes Name Value Digi-Key Part Number Description
C1 CAPACITOR GENERAL 0.01uF BC2662CT-ND CAP CER 10000PF 50V 10% RADIAL
C2 CAPACITOR GENERAL 0.01uF BC2662CT-ND CAP CER 10000PF 50V 10% RADIAL
R1 RESISTOR GENERAL 100K CF18JT100KCT-ND RES 100K OHM 1/8W 5% CF AXIAL
R2 RESISTOR GENERAL 10K CF14JT10K0CT-ND RES 10K OHM 1/4W 5% CARBON FILM
C3 CAPACITOR GENERAL 0.01uF BC2662CT-ND CAP CER 10000PF 50V 10% RADIAL
Q1 NPN P2N2222ARL1G-ND TRANS SS NPN 600MA 40V TO-92
R3 RESISTOR GENERAL 100K CF18JT100KCT-ND RES 100K OHM 1/8W 5% CF AXIAL
R4 RESISTOR GENERAL 10K CF14JT10K0CT-ND RES 10K OHM 1/4W 5% CARBON FILM
Q2 NPN P2N2222ARL1G-ND TRANS SS NPN 600MA 40V TO-92

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