Scheme features
The diagram of this detector is distinguished by ease of fabrication and the unusual way work:
- as an indicator used УSW (FM) receiver (64-108 MHz);
- as the search coil - cut cable TV.
Due to the fact that the generator on the VT3 transistor (low power transmitter) works at high frequency, to achieve high sensitivity and to simplify the coil design.
Schematic diagram and principle of operation
The coil is a coil of cable television 15-25 cm in diameter (in depending on the frequency and УSW range). You need to have in the receiver switchable AFC, which greatly increases the sensitivity (Fig. 2.27).
Fig. 2.27. Schematic diagram metal detector with indicator for УSW (FM) receiver (64-108 MHz)
To modulate the high-frequency oscillator multivibrator is used. Receiver tuned to the frequency of the metal detector so that she was on the edge of the strip passing. When approaching metal objects to the coil modifies the frequency of the generator and in the receiver the signal is lost.
Author: Martynyuk, N.