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2.70 Simple signal injector
Circuit 147: Simple signal injector
Setup information
Install the two transistors, the four resistors and the three electrolytic capacitors as shown in Fig. 2.147. The
nine jumper wires come next. Check the placement on the board again and then connect the battery.
Experiment
Our circuit here complements a signal tracker to form a small measuring system for NF circuits. The broad-
band spectrum generated ranges from 2 kHz up into the HF range. If you are familiar with the relevant
safety guidelines as per VDE and know how to observe them when working with devices that are to be
connected to the mains, you can now interconnect the circuit and an external circuit.
When you then touch the individual points of the circuits to be tested, you will hear the test signal loud and
clearly from the speaker of the test object, the responsiveness at such a point does not really matter. This
tool comes handy, if you need to quickly locate a broken level in an audio circuit. The circuit diagram for
this experiment is shown in Chap. 3, Fig. 3.147.
Components required:
2 x 2N3904 transistors,
2 x 2.2 kΩ resistors,
2 x 220 kΩ resistors,
2 x 10 nF ceramic
capacitors, 1 x 100 nF
ceramic capacitor,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.147: Simple signal
injector
173
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