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Spy Circuits http://\iwv. talkingelectronics.com'projecU.Spy%20Circuits/SpyCircui

The photo below shows the Field Strength Meter near the bug. The plastic knob on the trimmer allows adjustment without affecting the detecting Circuit. Simply tum the knob (with the two antennas near each other) and the 3 LEDs on the project will illuminate.

Spy Circuits http://\iwv. talkingelectronics.com'projecU.Spy%20Circuits/SpyCircui

Field Strength Meter and Bug

So far we have seen an unstable Circuit in action. Placing a finger near the bug will change the freguency. This is totally unsuitable.

A GOOD ONE TRANSISTOR CIRCUIT

The next Circuit uses a TUNED CIRCUIT or TANK CIRCUIT to create the operating frequency. This is clearly shown in the diagram. For best performance the Circuit should be built on a PC board with all components fitted close to each other. The photo below shows the Circuit using a coil etched on the board. This type of coil is totally unsuitable. It does not have a high "Q" and the rangę is very poor. The board cannot be touched as the capacitance of your body causes the Circuit to drift. A wound coil will improve the stability considerably. See photos below for the details of a wound coil.

Y

Artema

3v

A good one transistor Circuit