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Fisher World Treasure News From Our Archives Vol. 5, Issue 2 1996-1997

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The transmitter antenna of Dr. Fisher’s M-Scope was a coil of copper wire. Todays two-box detectors (like Fisher’s Gemini-3) operate on the same prlnclple, but they’re lighter, morę sensitive and easier to use.

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FIG. 7 RECŁIVLR CiffaUT

Plans for the receiver Circuit of the Fisher tubes connected to a coli of copper wire. The M-Scope metal detector show slx vacuum receiver Circuit was carrled In the forward box.

“Never have any large meta/ objeets, such as tools or tobacco tins, in your pockets while operating the M-Scope. ” —Dr. Gerhard Fisher

milliammeter and connect the end termi-nals of the 100-ohm shunt resistor between the meter terminals. Connect the sliding contact on the resistor to one of its cnd terminals. Mount the voltmeter, phonejack, switch and 6-ohm filament rheostat. Mount the batteries in the loop frame. G>mplete all conncctions.

Check all wiring tarefully, attach the carrying handles, adjust the transmiter position until it is approximately at righi angles to the receiver, tighten the wing nuts, then insert the tubes in the two units and tum on the switches. Adjust the re-ceiver filament rheostat until the reoeiyer voltmeter indicates 2 volts. You should now hear a rather loud and pleasantly pitched sound in the headphones. Adjust the condenser across the reccivcr loop for maximum volume, using a nonmetallic scre wdriver or a radio aligning tool for this purpose.

Now switch off the transmitter. The milliamme-ter reading should go up considerably. Adjust the slider on the milliammeter shunt resistor until you get a .95 meter reading. This will be the normal indica-tion of the meter when all adjustments have been properly madę and you are operating the instrument over territory which does not have any buried metal.

Tum on the transmitter switch again and have someone hołd the treasure-finder in a horizontal position about 2 feet above the ground in a location where there are no metal objeets. Tilt the transmitter to a position (either forward or baekward from the vertical), which will give the faintest tonę in the headphones and a maximum meter reading (this reading should be .95, sińce in this nuli position the recciver is getting very little signal from thetransmit-

FIG 6 TRANSMiTTĘP

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^he boxes and handles of the Fisher M-Scope metal detector were madę of the best and lightest materiał available: wood. The forward box, which contains

ter, but excessive use of metal in construc-tion may lower the reading slightly). Tighten the transmitter wing nuts again. A brass tumbuckle may be placed on one side of the transmitter box to kcep it rigid in tliis finał position. Finally, attach each ply-wood bottom panel with 5/8” brass screws.

This M-Scope has a veTtically-mounted transmitter and a horizontal receiver, but you can get eąually good balance with an approximately horizontal transmitter and an approximately vertical receiver, pro-vided you adjust the transmitter position as described above to ob-tain a balance. A coat or two of elear shellack or vamish over all ex-posed w'ood parts will improve the appear-

ance and give it protection.

It is best to try out your M-Scope first on buried pipes. Carry it with the recciver in front so you can w^ratch the milliammeter. Once you become familiar with the action of the instrument in the presence of metal objeets of various sizes, at various dcpths and at various distances to one side or the other of your path, you can procced to search unknown ground for buried treasure or minerał de-17 the receiver Circuit, Is set at a right angle to the rear transmitter box. This configu-ration creates a magnetic field that is disturbed by metal.

posits.

The tonę in the headphones will be loud-est and the milliammeter reading a minimum when they are directly over the buried metal. If it is an ore bed, the inerease in tonę volume and the decrease in meter reading may be gradual, but over pipes or buried treasure the volume will usually inerease suddenly. Never have any large metal objeets, such as tools or tobacco tins, in your pockcts w'hile operating the M-Scope.

To find the exact position of a buried objęci, approach the site from sevcral dircc-tions, marking on the ground each time the position where you get maxi-mum volume. The center of all these marks is the point to start digging.

Moisture in the ground, within reason-able limits, inereases the sensitivity of the M-Scope, and this is w'hy many prospec-tors and treasure seekers operate after a hcavy rain; the instrument itself must be kepi dry, however. If you get caught in the rain and moisture gets inside the units, re-move the bottom pancls and allow' the parts and wiring to dry slowiy in a warm place.

A finał, short section titled “Service Hints ” was also omitted from this article due to space limitations.—Editor