Do your dreams of locating buried treasures include vi-sions of finding a really
big onean old oaken chest full of gold and silver coins, or perhaps the hidden loot from a bank robbery? My files contain letters from readers who were searching for both. I once received a telephone call from a reader who was attempting to zero in on a multi-million-dollar cache of gold coins secreted underground somewhere in the Middle East. In each instance, the person who con-tacted me wanted to know if I could recommend some type of a metal de-tector with the ability to locate deep targets.
Answering such questions as these is difficult. Deeply-buried objects are difficult to locate. It takes a spe-cial type of detecting device to ferret out such treasuresan instrument with far greater capabilities than the type of metal detector which per-forms so well when used for coin-shooting, relic hunting, and more conventional forms of treasure searching.
My test report this issue concerns such a deep-seeking instrumentthe Gemini II, built by the Fisher Re-search Laboratory in Los Banos, California. Frequently called a two-box detector, the instrument consists of two components, a transmitter and a receiver, plus an aluminum carry-ing handle with which they can be linked together for operating pur-poses. Measuring approximately 9-by 12- by 3-inches each, the trans-mitter and the receiver can be latched together when not in use to form a compact package that is easy to transport or store. Total weight of the assembled unit is 9 pounds, and it balances well when suspended on the webbed carrying strap.
The transmitter and receiver are both powered by individual Eve-ready 1-276 (9-volt) batteries that are housed inside each unit. Equivalent batteries can be used as well. Esti-mated battery life is from 40 to 50 hours, and thats a lot of search time in the field. A built-in battery check is incorporated into each unit.
The Gemini II is designed to locate buried metal objects by detecting conductivity changes in the earth over which it is being carried. Ex-pressed in simpler terms, you might say that the transmitter sends out a radio frequency signal into the ground in search of metal targets. When such an object is located, an electromagnetic field is generated atound its surface, which is in turn picked up by the receiver. Positive responses are indicated by both an audio signal and the movement of a meter needle located on the receiving unit.
A positive response signifies the presence of a metal object, an ore vein or a mineral that is more con-ductive than the rock or soil sur-rounding it. Actually, this is pretty much the same as what happens with the operation of a standard VLF/TR metal detector.
Unlike a conventional detector which can sniff out single coins, rings and other small objects, the Gemini II is built to locate much larger objects at greater depths. Ap-plications in the industrial field in-clude the location and tracing of bur-ied metal pipes and cables, underground storage tanks and simi-lar large items. Prospectors and trea-sure hunters may find the instrument useful when searching for ore veins or buried riches.
Getting acquainted with the Gem-ini II is fairly easy. The position of the various controls and directions on how to use and adjust each are ex-plained in the instruction manual. Learning how to actually operate the unit is more difficult. The Fisher folks allude to this in the introduction to the manual, where they state
Successful detection, however, depends primarily on the skill and patience of the operator. It is very important that you thoroughly famil-iarize yourself with the Gemini II by following this instruction manual step-by-step.
Ill go along with the statement about needing to be completely fa-miliar with the instrument. But I think you will find the learning pro-cess a lot easier if you will follow a different step-by-step introductory process than the manufacturer presents. I suggest you commence by setting up to search in what is called the conductive trace, rather than the inductive trace as recommended in the manual.
I realize I may have tossed in a couple of unfamiliar terms, so lets improve your vocabulary. Inductive means that the transmitted radio fre-quency signal travels through the ground as it attempts to find buried objects. Conductive indicates that the signal is transmitted directly through a wire attached to an ex-posed portion of the object, and that the signal then comes back via the ground. During my field-testing ex-periences, I found that the conduc-tive method is by far the easiest to work with, so lets start our step-by--step journey here.
In order to operate in the conduc-tive trace mode, you will need a de-vice called a ground plate assem-bly, which consists of two 6-foot lengths of shielded wire (one red, the other black) attached to a single jack plug. A large battery clamp is af-fixed to the other end of the red wire.
A 4- by 5-inch flat metal plate is fas-tened to the black.
The ground plate assembly is available as an option. By all means order one. Or, if you are a handy-man, you can probably fashion one yourself. Either way, owning one will sure make your getting-acquainted process easier.
When used in the conductive trace method, the transmitter and receiver are not coupled together by the car-rying handle. To locate a buried pipe using this technique, insert the ground plate jack into the indicated plug on the transmitter. Now find a faucet or some other exposed portion of the pipe you wish to trace, then scrape clean a contact point. Attach the battery clamp to the pipe. Move the transmitter as far away from this contact point as possible (within the limitations of the 6-foot wire, of course) in a direction that is at right angles to the assumed direction of the buried pipe. Place the transmitter on the ground.
Continue on out with the second wire and insert the ground plate into the soil at a maximum distance away from the transmitter. Turn the mode switch to the Conductive Trace setting, then pull the power knob to activate the unit. Set the transmitter back on the ground in an upright po-sition. You are now sending signals through the wire and into the pipe.
Now, you have to pick them up.
To activate the receiver, set the range control at the low position on the dial, turn the sensitivity control to the zero position, then pull the power switch.
Start your search by holding the receiver vertically in line with the contact point, then commence cir-cling the area. The instructions say to stay at least 30 feet away from the transmitter, so as to eliminate the possibility of a direct air coupling be-tween the transmitter and the re-ceiver. However, this may not al-ways be possible. Do the best you can.
The secret to success lies in the proper usage of the sensitivity con-trol. This is an adjustment that must be monitored constantly. As you commence your search operation, turn the sensitivity knob to the point where the audio signal just appears. This is a critical setting that will vary with the distance between the re-ceiver and the transmitter. It is up to you to make the necessary fine ad-justments to maintain this audio sig-nal. Do not allow it to become too loud or too wide.
Continue following the circle pat-tern around the contact point until you hear a noticeable increase in the audio signal and the meter needle rises. This indicates you are in close proximity to the hidden pipe. To zero-in on the exact position, try lowering the sensitivity level until you receive a sharp, narrow signal.
Once you have located the pipe you can trace its position by moving
further out along the same line of di-rection. As the distance from the ex-posed contact point increases, you will probably note a decrease in sig-nal intensity. To restore the audio re-sponse, increase the amount of sensi-tivity. Moving closer to the contact point will cause a louder, broader signal, so you will have to decrease the sensitivity in order to maintain that sharp, narrow audio response.
I realize that this may sound rather complicated, but it really is not that difficult to learn. And it is a great way to gain confidence in the Gemini IIs ability to locate and trace pipes.
After attaining a feel for the instru-ment while employing the conduc-tive mode, I recommend you now try to find the same pipe using the narrow-scan inductive search tech-nique explained in the instruction manual. This time you will need to fasten the transmitter and the re-ceiver to the aluminum handle.
Directions for completing the as-sembly are outlined in the instruction manual, together with explanations on how to adjust both the transmitter and the receiver. The manual also ex-plains how to set up and adjust the Gemini II for narrow-scan searching, wide-scan searching (which is a two-person operation) and for tracing a pipe using the inductive process. The explanations are fairly clear, but they do not point out some of the difficul-ties you are likely to encounter as you put them to use. Rather than re-peating the same step-by-step direc-tions outlined in the book, lets con-sider some of the problems.
A noticeable difference between the Gemini II and your ordinary metal detector is found in the place-ment of the transmitting and receiv-ing coils. In a conventional detector, both coils are located within the loop. In the Gemini II, the antennas are in the form of metal rims posi-tioned on separate boxes.
When the Gemini II is rigged for inductive searching, which is the proper procedure for treasure search-ing, the transmitter and the receiver are separated by the 4-foot-long alu-minum carrying handle. This means you are not able to pinpoint a target directly under a loop.
Instead, you must find the object by performing a two-directional walk process and make marks on the ground according to signal intensity. The object you are seeking will be centered between these two points. It is a rather tricky operation that takes some getting used to.
Another problem lies in the man-ner in which the instrument tends to sound off if it is not held level as you walk along while searching. The phenomenon reminds me of the au-dio response you-get when you lift or lower the loop of a standard metal detector when searching in the TR mode. The noise can be confusing, but it is something you must learn to accept.
If I were only interested in locating or tracing water pipes Id stick with the conductive trace method, be-cause it is a lot easier. However, bur-ied pipes were not what the folks had in mind when they asked me for in-formation about a deep-seeking search device. So it is imperative that you learn how to master the induc-tive search techniques if you hope to find hidden treasure chests. Unfortu-nately, objects of this nature do not come with exposed contact points on which you can attach a battery clip.
Not having a treasure chest to use as a target during my field-testing en-deavors,, I tried to make do by a sim-ulation process. Using a post-hole digger, I spun a 4-foot-deep hollow in the back yard. I then filld an empty 1.5-litre wine jug with Memo-rial pennies, tied a rope on the han-dle, then lowered it into the excava-tion. The results were not all that promising. I could not get a reading on my cache much beyond a 12-inch depth.
Ill be the first to admit that my jug-in-an-open hole test may not have been too meaningful. After all, a bottle of coins suspended in a verti-cal direction is a much smaller target than a chestful of riches. Checks conducted on a much larger 350-gallon fuel tank buried several feet deep did produce the proper signals.
Factors which influence the Gem-ini Its ability to locate buried objects are pretty much the same as those which determine the performance of a standard metal detector. Ground mineralization, the size and shape of the object, the length of time it has
been buried and the skill of the indi-vidual operator must all be reckoned with. None of these should be ig-nored or taken lightly. The instru-ment is not a miracle machine and if you hope to bring out its maximum capabilities you must learn how to use it.
Does Gemini II belong in your ar-senal of search tools and weapons? If you require such a deep-seeking in-strument for tracing pipes, cables or other industrial usages, the unit will do the job and you can probably write off the $459.95 cost as a busi-
ness expense on your income tax re-port. Should your sights be set mUch higher and you are looking for an ore vein or some form of buried treasurewell, you may need all the assistance you can get. In such situa-tions, the Fisher-built two-box may help lead you to those riches.
Should you be fortunate enough to hit the big one, that price tag reading will be a minor matter. Youll have far more important things to work out with the Bureau of Internal Revenue. Ah, to be so lucky! 0