When the receiver is tuned to a M. W. radio station the resulting feedback howl, caused by the transmitter can be set to alter, or appear when the coil and radio are above or near a metal object Here is a pictured of the search head. It is made from a margarine tub. the small radio receiver is fitted inside the cover which is the wound coil on a disc
METAL DETECTOR - schematic

. This is the schematic for the transmitter circuit which is housed in the box near the handle. The coil L1 is actually in the search head. the wires for this and the ear phones run down the handle hollow tube. I originally made this detector for the fun of doing the electronics and had no experience in the treasure seeking aspect of metal detectors. My son Bobby has this experience, so I decided to accompany him on a treasure hunt. We spent a whole Sunday afternoon searching a field which had been earmarked for house building and was lying redundant. My son was in charge of the spade work which pleased me, as this can be quite hard work on uncultivated ground. I operated the detector and found this, like fishing, completely addictive, with the well known, " just another five minutes" syndrome. The fading daylight finally finished the search for the day. The field lay alongside the railway lines and we started at the gate and walked along parallel with the lines, immediately the machine started to signal and did so every few minutes. after turning up many bolts nuts nails and scrap metal we came to the conclusion this was the area the railway workmen had used, and moved into the middle of the field. We now started to find more interesting items The first was a pocket knife in nice condition, I was intrigued by the stain at the tip of the blade It could have been blood or maybe tobacco. Later a brass button slightly bashed...

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