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Fisher World Treasure News From Our Archives Voł. 5, Issue 2 1996^1997

A Fisher metal detector you can make

By Dr. Gerhard Fisher

I am rcvcaling in this article the actual Circuit and constructional data for my M-Scope radio treasure-finder. This unit has proved over and over again that it can locate buried treasure and minerał deposits. Imitations of M-Scope units, madę without the detailed information presented here, may give poor results, which will indircctly reflect upon my theorics and circuits. Any reader of Science and Mechanics may build an M-Scope for his own, non-commercial use, but this instrument is protected by U.S. Patent No. 2166561. Building a unit for sale or for rental to otlier persons would violate the patent rights.

The M-Scope is inexpensive and easy to build, for it uses only conventional radio parts.

It is battery operated because one of the re-quirements is that it be sufficiently light in weight so one person may carry it for hours without fatigue during a hunt for treasure.

The M-Scope contains two separate

1939 artlele reveals Plans for M-Scope

Donated by Bill Kerr of Baytown, TX

This article, written by Dr. Gerhard Fisher, founder of Fisher Research Labo-ratory and titled “Plans for Radio Treasure-Finder, ” appeared in the February 1939 is-sue of Science and Mechanics Magazine. It describes how to make your own two-box metal detector at home.

Here are some excerpts from this article that no w serves as a snapshol in time of detector evolution.

Plans far Radio Treasure Finder umts mounted on a single hardwood carry-ing frame.

1.    A two-tube radio transmitter which feeds a 170-kc. carrier signal (modulated with a 1,000-cycle tonę) into the transmitter loop aerial.

2.    A radio receiver which picks up the transmitter signal and feeds it, after ampli-fication, into a vacuum tubę voltmeter and into headphones.

The two units are arranged on the car-rying frame so that, when there is no metal in the vicinity, no signal is picked up by the receiver. When there is metal in the ground, the balance between the units is upset. 'The receiver measures the amount of unbalance, and the rneter reading is a guide to the amount of metal and its distance away from the treasure-finder. At the same time, headphones in the receivcr circuit rcproduce the 1,000-cycle transmitter tonę, and in-crcased loudness indicates the presence of metal.

Wlrlng and Transmitter

(Sections titled “Making the Wood Parts, " atid “Carrying Handles” have be en omitted here to save space.)

The following procedurę is recom-mended for completing the transmitter:

Connect the 3-meghom resistor. Con-nect the two paper condcnscrs and the mica condenser. Wire the filament terminal s in parallel. Fasten the chassis to the cleats in the transmitter loop frame with screws, placing the socket end elosest to the loop leads. Connect the loop leads. Mount the R.F. choke either on the chassis or the front panel. The three R.F.

The electronic prospector of the 1930’s was obvlously a styl-ish dresser as ev!denced by this illustration taken from the February 1939 Science and Mechanics magazine. The caption that ran beside it was the following: “The transmitter and receiver of the M-Scope may be mounted on the carrying handles as shown. Results will be essentially the same as with the arrangement shown in Fig. 5 [next page]. In each case, the operator faces the receiver unit whlle prospecting for treasure.”

chokes reąuired for this M-Scope are spe-cial units, each having 1500 tums of No. 34 enamel wire either random or duo-lat-eral wound, so be surę to give this data when ordering. Mount the voltmeter and the switch. Błock the batterics in position insidc the Ux>p frame, using wood cleats. Make connections to the R.F. choke, switch, rneter and batteries.

The following procedurę is recom-mendcd for completing the receiver:

Connect all carbon resistors. Connect all fixed condensers. Connect all filament terminals in parallel. Mount the chassis in the rcccivcr loop frame wMth the input tubę socket elosest to the loop leads. Mount the 200-600 mmfd. adjustable condenser on the insidc of the loop frame just above the l<x>p leads. Connect the loop leads to this condenser and to the first tubę. Mount the

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