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Summary of Contents for Fisher Research Labs Gemini-3
- Page 1 Gemini-3 2-Box Metal and Mineral Detector for Deep Search and Cache Locating Operating Manual...
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Page 2: Table Of Contents
CONTENTS About Your Gemini-3 ............... pg. 3 Basic Theory of Operation ............pg. 4 Depth ..................pg. 5 Transmitter ................. pg. 6 Receiver ..................pg. 7 Searching .................. pg. 8 Narrow Scan Inductive Search ........... pg. 8 Set Up ................pg. 8 Tuning ................ -
Page 3: About Your Gemini-3
Fisher Research Laboratory is the recognized leader in the field, in fact, they were granted the first two-box metal detector patent over 60 years ago. You might think it would be difficult to improve on a product that has been in a constant state of development for so many years. But the fact is, the GEMINI-3 is probably the biggest leap forward in two-box design since it replaced vacuum tubes with transistors back in the 1950s. The new GEMINI-3 goes 10 to 20 percent deeper than its predecessor. It will trace most pipes and ore veins at least 50 percent farther, and the new crystal controlled circuitry is rock stable. The old metal-rim antenna is gone and so are the hard-to-get batteries. The GEMINI-3 is easier to use,... -
Page 4: Basic Theory Of Operation
When used in any of the Inductive modes, the RF signal travels through the ground to the object. When used in the Conductive Trace mode (see page 15), the signal is transmitted directly through a wire attached to an exposed portion of the object. The function of the GEMINI-3 Receiver is to locate the object by detecting the electromagnetic field around it and responding with audio and visual signals. -
Page 5: Depth
DEPTH The GEMINI-3 was designed to locate large, deep objects such as an iron chest, pipe or an ore vein. It will not detect small coin- sized objects. A quart jar full of coins, however, may be detected one-to-three feet deep. A 55-gallon drum may be detected as deep as 10 feet. A very large object, like an automobile, may be detected at 20 feet or more. The ability of the GEMINI-3 to detect objects at various depths depends on several factors: 1. Ground Mineralization: The penetrating power of the GEMINI-3 is adversely affected by the presence of magnetite (a black iron oxide) and wet conductive mineral salts. For example, an object that can be detected at 15 feet in neutral ground may be detected no deeper than 5 feet in highly mineralized ground. 2. Size and Depth of Object: A 4-inch diameter target will produce signal 64 times stronger than a similar 1-inch diameter target at the same depth. An object 1-foot underground will produce a signal 4,000 times greater than the object 4 feet deep. 3. Length of Time Object is Buried: An object that has been buried for a long time may be easier to detect than a newly buried object. Rust and other oxides as... -
Page 6: Transmitter
TRANSMITTER Power Switch: Pull out switch turns on power. Ground Plate Jack: Used with the optional Ground Plate Assembly for the Conductive Trace Mode. Battery Level Meter: Gives a visual indication of battery strength. Replace batteries if below 5 on meter. Battery Level Meter Power Switch Ground Plate Jack Figure 2. Transmitter... -
Page 7: Receiver
RECEIVER Speaker: Provides audible indication of the receiver signal for balancing and detecting. Meter: Provides visual indication of the Receiver signal response for balancing and detecting. Also used as a battery test indicator. Sensitivity Control: Used to control sensitivity level. The circled “7” indicates the starting level used for Narrow Scan Inductive Search Mode. Headphone Jack: Accepts stereo or monaural headphones and silences speaker when headphones are plugged in. (Stereo/mono headphones should be in “stereo” position.) Power Switch: Pulling switch out turns on receiver. Meter Speaker Sensitivity Control Battery Test Switch Power Switch Headphone Jack Figure 3. Receiver... -
Page 8: Searching
SEARCHING Narrow Scan Inductive Search This mode of operation is performed by a single operator using the 3-piece handle. It is the best method for locating small or short objects (chest, coin-jar, rifle, etc.). However, it is also an effective way to locate pipes, cables and ore veins. Set Up 1. Assemble the 3-piece handle by inserting each end piece into the center handle section. Tighten the two center knobs finger tight until there is no wobble. Place the transmitter on its back and insert the end of the handle with the single brass shaft into the V-shaped slot. Turn the knob until it is finger tight and the handle is firmly in the slot. 2. Align the receiver panel holes with the upper- handle threaded shafts. Tighten the lower black knob until it is finger tight. 3. Turn the balance knob (with white arrow) until the spring is under tension (at least 10 turns). Figure 5. Assembly for Narrow Scan Inductive Search Figure 4. Narrow Scan Inductive Search... -
Page 9: Tuning
. Set the transmitter: Power: ON Set the Receiver: Power: ON Sensitivity: 7 You should get a strong audio tone and meter indication at this point. CAUTION: Never attempt to tune the GEMINI-3 in the presence of metal objects likes cars, metal walls, roofs or heavy metal reinforcements in any structure. Their presence will make proper balancing impossible. . Pick the unit up by the handle and balance it so that it is level with the ground and at normal carrying height (arm’s length). Five cm higher in the front is OK. For a deeper search, attach the fully lengthened... -
Page 10: Operation
SEARCHING You are ready to search when the BALANCE knob is adjusted within the 1/8- to 1/4-turn silence (null) space. This is extremely important! If this procedure is not followed correctly, the GEMINI-3 will either constantly give false audio and meter readings (sensitivity too high), or no signals at all (sensitivity too low). The sensitivity will be correctly set and your GEMINI-3 will operate properly only when a 1/4- to 1/8-turn null has been achieved. If you lower or raise your GEMINI-3, you may have to retune by making repeated adjustments to the BALANCE knob and/or the SENSITIVITY control. - Page 11 Small or deeply buried objects such as a Figure 6. Handle strap: Using cache of coins, require a tight, closely the handle strap increases traversed search pattern. Large or shallow depth; however, it may be objects can be located successfully with difficult to tune the GEMINI-3 this close to highly mineralized a larger, more widely traversed search ground. pattern.
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Page 12: Wide Scan Inductive Search
SEARCHING Wide Scan Inductive Search This mode of operation is the preferred method for searching a large area quickly. Two operators are required and the handle assembly is not used. The Wide Scan Inductive Search mode is practical only when searching for ore veins, pipes or cable 40 feet long or more. If the operators are too close together, “direct air coupling” will result, meaning the receiver is detecting the Transmitter signal directly through the air instead of through a buried conductor. -
Page 13: Operation
SEARCHING 3. Slowly increase the SENSITIVITY control until the audio signal is heard, then reduce SENSITIVITY until the audio just disappears. This is the point at which “air coupling” has been eliminated. Operating 1. Keeping the receiver and transmitter sections in line, the two operators can now walk their predetermined search pattern. The SENSITIVITY control should be checked periodically to ensure that the receiver is tuned just below the “air coupling” threshold. 2. If both operators cross the same conductive body (pipe, cable, ore vein, etc.) at approximately the same time, the receiver tone and meter will rise to indicate its presence. The receiver operator should alert the transmitter operator that they have detected a conductive object. 3. The receiver operator should then hold his position while the transmitter operator moves back and forth for the strongest receiver response. At this point,... -
Page 14: Tracing
TRACING Inductive Trace The Inductive Trace mode is usually used to trace a long object (pipe, ore vein, etc.) that shows no exposed portions, but two starting points are known. Set Up Locate two points along the conductive object at least 30 feet apart as described in the Wide Scan or Narrow Scan Inductive Search sections. The transmitter and receiver should be in line with each other, both facing the same direction. The transmitter should be on the ground and the receiver should be held by the operator. Figure 8. Inductive Trace Tuning 1. -
Page 15: Operation
TRACING Operating 1. Once the two starting points have been established and the receiver tuned, walk away from the transmitter in the assumed direction of the buried conductor. 2. Hold the receiver vertically to maintain a peak signal or horizontally, face up, to maintain a null or minimum signal. Either method indicates that you are over the object and tracing its path. 3. As the distance from the transmitter increases, the signal will fade. As this occurs, increase the SENSITIVITY as required. 4. When the signal becomes too weak to trace, stop and move the transmitter closer. 5. Be aware that if you are tracing a pipe, each time a “T” junction or lateral is encountered; the signal will split and weaken. Conductive Trace This is the best method for tracing a single pipe in the presence of other pipes. A portion of the pipe must be exposed in order to energize it by direct connection utilizing a Ground Rod Assembly (not included). Set Up 1. If possible, clean the contact point of the pipe with a wire brush. 2. Connect the ground plate clamp to the contact point. -
Page 16: Tuning
TRACING Tuning 1. Set the transmitter: Power: ON 2. Set the receiver: Power: ON Sensitivity: ZERO 3. Slowly increase the SENSITIVITY control until the audio signal is heard, then reduce SENSITIVITY until the audio just disappears. This is the point at which air coupling has been eliminated. Operating 1. Locate the buried pipe by circling the contact point, keeping the receiver in line with the contact at all times. Stay at least 30 feet from the transmitter. 2. Once the pipe has been located by a sharp increase in audio and meter signals, the pipe may be traced exactly as described in the operating section of the Inductive trace instructions. -
Page 17: Prospecting Tips
Note the character of the overburden, outcrops and topographic features. When the area being inductively surveyed has been completely covered and all of the conductive zones have been staked, these zones are surveyed and plotted on a map. The map should include all creek bottoms, gullies, outcrops and other physical features. The ideal map on which to plot the conductive zones is a topographic and geological map of the proper scale. In this way it is possible to correlate the zones directly with the topography and geology, and thus determine the possible reasons for the presence of the various conductive zones. Locating Placer Deposits A lot of prospectors have told us they would like to use a two-box for locating placer gold. In general, these deposits contain such a small amount of gold that it cannot be detected. Placer gold, however, is usually associated with a certain amount of black sand, and some placer deposits carry iron sulphide. Both of these mineral substances are definitely conductive, and may be detected by the GEMINI-3. It is through the detection of these minerals that the placer gold may be located. -
Page 18: Sources Of Error
The most common nonproductive zones of conductivity are: 1. Dissolved mineral salts - Mineral salts become conductive when dissolved in water. As a result, the presence of saline water or water saturated soil high in salt content may render the GEMINI-3 useless. 2. Rough terrain - In very rough terrain it may be difficult to maintain the GEMINI-3 parallel to the ground, resulting in frequent false signals. 3. Irregularities in the overburden bedrock - The GEMINI- 3 may detect sharp changes in conductivity which are of no important geological significance. 4. Fault zones - Fault zones often give positive indications because they are highly fractured and usually contain concentrations of water and minerals. -
Page 19: Battery Replacement
BATTERY REPLACEMENT 1. Turn either instrument (Transmitter and Receiver) over on its face and remove access plate with coin or large blade screwdriver. 2. Lift the battery pack out carefully. Turn the battery pack slightly, unsnap the battery connector and slip off the sleeve. Change all eight batteries. Slip the sleeve back on, then reattach the connector to the pack. Slip the battery pack back into its compartment and do a battery test. Refasten the access plate. Both the transmitter and receiver will work from 30 to 40 hours on a set of 8 standard quality, carbon-zinc batteries. Alkaline batteries will give substantially longer life and in cold weather will perform much better than standard carbon zinc batteries. -
Page 20: Treasure Hunters' Code Of Ethics
TREASURE HUNTERS’ CODE OF ETHICS LET’S PRESERVE OUR TREASURED SPORT! Laws governing the use of metal detectors are common in some areas. In many countries, the use of metal detectors is illegal or severely restricted. DON’T LET THIS HAPPEN IN YOUR COUNTRY! • Always check Federal, State, County and local laws before searching. • Respect private property and do not enter private property without the owner’s permission. • Take care to refill all holes and leave no damage. • Remove and dispose of any and all trash and litter found. • Appreciate and protect our inheritance of natural resources, wildlife and private property. • Act as an ambassador for the hobby, use thoughtfulness, consideration and courtesy at all times. • Never destroy historical or archaeological treasures. • All treasure hunters may be judged by the example you set; always conduct yourself with courtesy and consideration of others... -
Page 21: Where To Use Your Metal Detector In The U.s
Where To Use Your Metal Detector In The U.S. National Forest and Federal Lands—Metal detecting is allowed only by special permit acquired from the federal government. Each area has a district office. Corps of Engineers, Lakes, Shorelines and Lands—Permission has been granted only on pre-disturbed sites, such as beaches and attached swimming areas. New Corps lakes and lands must be okayed by the main office of the Army Corps of Engineers. Each area has a district office. State Parks and Lands—Some state parks are open to metal detecting, but some are not. Always check with the park ranger before attempting to use your detector. Bureau of Land Management (BLM) Lands—Some areas are open for metal detecting, and some are not. Always check with the district office. -
Page 22: Specifications
SPECIFICATIONS Dimensions Length on handle ............49 1/2 inches Transmitter-Receiver Box Assembly ..........9 1/4 x 12 x 6 inches(23.5 x 30 x 15 cm) Weight Complete ................7 lbs. (3.2 k) Transmitter ................2.4 lbs. (1.1 k) Receiver ................2.9 lbs. (1.3 k) Handle ................1.7 lbs. (.75 k) Frequency RF Search and Trace ......81.92 KHz Crystal Controlled .......... Audio Target Response (V.C.O.) Operating Modes Search 1. Narrow Scan, Inductive 2. Wide Scan, Inductive Trace 1. Inductive 2. Conductive Target Response Meter ............2 1/4 x 1 3/4 inches, Analog Speaker ............2 1/4 inches, 100 ohm, Moisture Proof Cone Headphones .......... 1/4 inch Jack, 8-16 ohms, ....................Stereo/Mono Batteries Receiver ................ (8) AA 1.5V Transmitter . -
Page 23: Using Headphones
SPECIFICATIONS Notes 1. Subject to improvement or modification without notice. 2. Approximate. 3. Voltage Controlled Oscillator. Volume and pitch both increase as target is approached for easier, more accurate pinpointing. 4. With optional ground plate assembly. 5. Optional stereo/mono headphones. 6. Use of headphones will significantly increase battery life. Fisher Research Laboratory does not warrant suitability to specific use. Fisher Research Laboratory shall in no event be liable for any direct, incidental, consequential or indirect damages. USING HEADPHONES Using headphones (not included) improves battery life, and prevents the sounds from annoying bystanders. It also allows you to hear subtle changes in the sound more clearly, particularly if searching in a noisy location. For safety reasons, do not use headphones near traffic or where other dangers are present. This device is to be used with interconnecting cables/headphone cables shorter than three meters. - Page 24 Q U A L I T Y Fisher detectors are renowned for their quality. Each detector is hand crafted in the USA with pride P E R F O R M A N C E The worldwide underground utility industry relies on Fisher ® Our instruments are durable, dependable, and locate deeper. R E P U T A T I O N Fisher produced the first patented metal detector in 1931. For over 80 years, the Fisher logo has been a mark of excellence. 5 - YEAR LIMITED WARRANTY Register your warranty on-line for a chance to win a FREE DETECTOR.
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