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Metal Detector

Metal Detector FAQ - Frequently Asked Questions - Metal Detecting and Metal Detector Questions and Answers? 

FAQ - Metal Detecting and Metal Detector Questions and Answers?

Jack Gifford, founder and owner of Tesoro Electronics Answers some common questions about metal detectors and metal detecting. Please feel free to print out this document for your metal detecting library!


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How deep can a good metal detector be expected to find coins?

This question is much easier to answer today, due to the fact that virtually all of the detectors made today are of the "motion" or VLF Discriminator type. Most of them come with a searchcoil of around 8 inches diameter, since this size has been determined by most everyone to be optimal for coin hunting in areas with moderate amounts of trash. Using the proper sweep speeds for the detector type will also affect depth, but the following figures are achievable for a properly used detector.

Target size: Depth:
Dime to Nickel: 4 to 8 inches
Quarter to half dollar: 6 to 12 inches
Dollar to fruit jar lid: 8 to 16 inches
Other conditions affect how deep your detector goes, but those same conditions will also affect all other detector's depth. Becoming familiar with your detector and using it at the proper sweep speed are the two most important things for you to do.


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Can any one metal detector really "do it all"?

Some of the better "all-purpose" detectors do a pretty good job at most hunting chores, but there are some specialized types of hunting where they generally are not as effective as models designed for that particular purpose. Waterproof detectors and nugget machines are two types that are specialized, and pretty much not compatible with all-purpose detectors. Diving and wading takes a detector which can handle being wet, and nugget hunting, for all practical purposes, means using a VLF All Metal detector with extreme electronic gain.

All of the manufacturers make several different types of detectors to cover all hunting applications. Their literature will clarify which type of hunting each of their metal detectors were designed for. If it doesn't say, it should be a "general purpose" type.


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Are detectors with a lot of knobs better than those with just a few knobs?

Regardless of a metal detector's purpose, it will all fall into one of two
different classifications,
a) "turn-on-and-go," or b) "do-it yourself." Turn-on-and-go detectors have either a factory preset ground adjust or automatic ground adjust, and do not require any adjustments by the operator for mineral conditions. The electronic circuitry takes care of eliminating any mineral effects.

The do-it-yourself types generally have a multi-turn Ground Adjust control, which must be properly set by the operator. This type is generally capable of just a little more depth than the turn-on-and-go types if it is set properly, but can yield much worse results if it isn't adjusted properly. Both types can be very effective detectors.


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What kind of detector should be used for gold, relic or coin hunting?

Gold, or nugget hunting, is best done with a special nugget detector. Since there is an awful lot more tiny pieces of gold than big ones, most nugget machines have an extreme amount of electronic gain to find the really tiny pieces close to the coil. This extra gain doesn't translate into much added depth at all for coin sized objects, however. Most nugget detectors don't have any Discriminate modes of operation, since to find gold almost requires you to search in the All Metal mode. Nugget hunting is possible with a good all-purpose detector, but you won't find the little tiny pieces that a nugget detector will find.

An all-purpose detector is all that is re required for Relic or Coin hunting, although larger coils may be desirable for Relic hunting. For Coins, there are other features which may be desired, such as Discrimination, Notch Discrimination, Target ID, Coin Depth, etc. Obviously, for Coin hunting, Motion Discriminate mode is necessary since you don't want to dig all of the iron bits you are likely to find. All of the other option are simply "at your discretion."


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Why are there so many types of searchcoils?

The two most popular styles of coils today are the Concentric and the Wide Scan. The Concentric is a much better discriminating coil than a Wide Scan, but is much more affected by the ground you are hunting on. It generates a much more uniform field than a Wide Scan and is the type generally used on most detectors built today.

The Wide Scan coil, though, since it is less affected by the ground, can be a much superior coil in areas of high mineral concentrations. While it lacks a little bit in finding the absolutely tiniest bits of gold, Tesoro uses this style as standard on its Lobo and Diablo II nugget hunters.

Both coil configurations are built by Tesoro in round versions for its all-purpose detectors and in elliptical versions for its nugget hunters. Each shape (round and elliptical) uses a different connector, as they are not interchangeable with each other.


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Which coil size is best?

Most nugget hunters use either the 10 inch Wide Scan (standard) coil or the optional 7 inch Concentric coil. We make a 15 inch elliptical coil size in either Wide Scan or Concentric for finding coin size targets a little deeper.

For the all-purpose detectors, the standard coil that the detector comes equipped with is usually the optimum size for most hunting. In extremely trashy areas, a smaller coil (4" or 7") usually will bring better results. The reason for this is that even though the smaller coil has less depth for coin sized targets, good targets will not be masked out by bad targets lying next to or over them.

And if you get into a relatively clean or trash-free area, a larger coil (10 1/2", 11" or 15") will usually yield better depth and a wider area of coverage when trash masking of good targets isn't likely to be a problem.


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How much discrimination should I use?

If you are serious about finding gold rings and gold coins, use as little discrimination as possible. I recommend setting the discrimination level to be just below nickels. All gold items are lost at about the pull-tab level of discrimination, so by eliminating pull-tabs, you are also losing all of these gold targets. Even if you use a Notch Discriminator to eliminate pull-tabs, you will lose all of the gold targets which have the same phase response as the pull-tabs.

A truly serious hunter, and one who has been successful over the years, will have dug many, many pull-tabs. But that is why he has also found most of his gold targets. I know of several excellent hunters who still hunt in All Metal mode. While they're digging a lot of trash, they are also finding some incredible targets. With today's motion machines, it is pretty easy to get rid of most of the iron objects, but those iron objects could be hiding good targets below them.


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What is the purpose of Notch Discrimination?

Notch Discrimination can be used to either reject a narrow band of targets (notch reject) or to respond only to a narrow band of targets (notch accept). It is usually used to reject pull-tabs while still finding nickels and the gold rings which do not have the same phase response as pull-tabs. The Notch Level control generates a "window signal," whose width is set by a small control on the PC board. This "notch window" can be moved up and down the discriminate range, until it properly covers the desired range of target response.

If the detector is being used to eliminate the response to pull-tabs, you need to remember that any good target with phase response which fall within the window will also be eliminated. Such targets consist mainly of gold items and rings.

The notch accept feature can be used to tune the detector to a particular type of item, such as a known type of ring. The detector then will only find items which fall within the narrow notch window.


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Does using Notch Discrimination cause a loss of depth?

Yes, it can cause a small loss of depth due to two reasons. The first reason is that the notch discriminator adds a slight amount of capacitance to the normal discriminator circuit, which slows the response somewhat. This effect can make sweep speeds more critical when it comes to finding deep targets, but if the detector is used properly, it will not cause much loss of depth at all. The other reason depth is lost, is that as a target approaches the response cutoff of the filters used, its signal strength becomes greatly diminished. Setting the bottom edge of the notch window too close to the nickel will cause some loss of depth on the nickel, and setting the top edge too close to the penny will cause some loss of depth on the penny. A properly adjusted notch window will not cause a great deal of depth loss however.


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How do I adjust my Sensitivity control to get maximum depth?

The Sensitivity control of your detector can affect just the All Metal mode, just the Discriminate mode, or both modes. Its purpose is to decrease the electronic gain of the stage it affects enough to make the detector more usable. If you are uncertain which modes of your detector are affected by the Sensitivity control, just tune the detector according to your operator's manual, and wave a good target over the coil. If you can detect it farther away with the Sensitivity control at maximum than you can at minimum, the control affects that mode.

Regardless of which mode you are using, the Sensitivity control should be as high as possible without causing many false signals or sputtering noises while searching . When these signals are present, it makes hearing the weak responses of good deep targets difficult.


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What is Target ID and how does it work?

If you have any kind of discriminating metal detector, you have a "do it yourself ID" available. By increasing the discriminate level control until the target just disappears, you can tell what the target is. A Target ID detector does all of this automatically and very rapidly as you swing the coil over each target. Basically, the electronics circuitry measures the phase angle of the target as the signal happens. It generally takes only one pass over the target to get accurate ID, although the earliest types took several swings, which is why they were known as "pump up" ID detectors.

Target ID is a very accurate measure of the target's phase response, but unfortunately many targets have identical, or nearly so, target responses. That is why you will lose a lot of good gold rings if you believe your ID is correct each time it tells you the target is a pull-tab. The ID is just another form of information that you, the operator, must interpret before deciding whether you will dig the target.


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Is manual ground adjust better than "automatic" or "preset"?

Typically, you can get just a little bit more depth from your detector by properly adjusting the Ground Control of a manual type detector than you could expect from a factory set or "automatic" type of turn-on-and-go detector. The preset machines will always get good performance no matter what type soil you are hunting in. Adjusting the manual machine may increase the detection depth a small bit, if it is done properly, but if it is not done properly, the results may be horrendous. I feel that for the average detector user, a preset or automatic detectors performance is superior to the results which may be obtained with an improperly set manual machine.


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Are battery test readings accurate?

Only if the battery test is done while the batteries are delivering the proper amount of current to a load. Some "drug store" battery testers, as well as a good volt meter may yield completely erroneous results due to the fact the batteries are not delivering current during the test. An audio battery test is probably the best, since the audio circuitry loads the battery to the detectors maximum amount of power delivered while the test takes place. Also since batteries can tend to rejuvenate some of their performance after a long rest, it is best to test the batteries after they have been used for at least ten minutes.


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How can I judge whether I should buy NiCads or Alkaline batteries for my metal detector?

Carbon Zinc and Alkaline batteries are the two types most readily available, and their cost should be a lot closer today than several years ago. To judge for yourself how much they cost, use a set of each type, keeping track of the number of hours of use you get from each type. Divide the cost of the set of batteries by the number of hours of use they provided. This will tell you which offers the best performance in your detector.

NiCads are available in almost all battery styles today, and offer a much better price/ performance ratio if you use at least one or two sets of batteries per month. Using less than one or two sets means that you will not recover your initial investment as rapidly.

NiCads can be very noisy in some detectors, and also have a "memory" characteristic if they are not fully discharged each time they are used. I prefer Alkalines, since they don't exhibit any of these characteristics.


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What is the best way to pinpoint a target?

Instruction manuals usually show you how to pinpoint by "X-ing" the target. This can be done by using a side-to-side sweep and a front-to-back sweep or approaching the target from several angles. As each sweep is completed, note the spot where the signal is strongest, where the imaginary lines cross, and dig.


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How much will using headphones increase battery life?

The current necessary to drive a set of headphones is considerably smaller than that required to drive the low impedance speaker. The speakers in most metal detectors are of 8 or 16 ohms impedance, while most detectors use a resistor of approximately 100 to 200 ohms to limit the sound output in the headphones. Using the numbers quoted, a set of headphones should result in an increase of approximately 2 to 3 times the operating life. Since the electronics circuitry is always operating, even though the detector may not be making noise, the savings is not as big as the numbers would indicate.


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Are there any good places left to hunt?

There are an awful lot of areas that seemingly have been "hunted to death," but if a person is patient, there still are probably some nice targets left almost everywhere. Spending some time doing a bit of research can turn up places which may never have been touched. Beaches are well worth trying, especially after a storm churns them over.

There are a number of good books written by various authors about finding the un-worked spots. Your metal detector dealer probably sells at least one of them.

One thing worth remembering is that nobody gets it all. Just because an area has been hunted several times doesn't mean that there is nothing left.


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What is the difference between 2-filter and 4-filter metal detectors?

The first Motion based discriminators were of the so-called 4-filter type. These detectors had to be swung almost as fast as a golf club to get maximum depth. The newer so-called 2-filter types do not need to be swung nearly as fast for maximum depth.

The names of these detectors are a misnomer, since they both generally have the same number of filters. Basically, the more modern slow sweep units generally use a filter consisting of a 2-pole configuration. The older types used a configuration more in line with a 4-pole filter. Since the average detectorist doesn't understand the difference between 2 poles or 4 poles, the name was changed to 2-filter and 4-filter. I don't know why, because the average detectorist still doesn't know the difference between 2 filters or 4 filters, does he?

At any rate, the 4-pole filter will have a much sharper cutoff rate between signals that get through and signals that don't. But the cutoff rate isn't really that important, and since 2-pole filters are easier to build, they seem to have won out.


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My VLF metal detector sometimes detects rocks and tree roots.
Is this normal?

A lot of this kind of performance may be normal, but some of it may not. Basically, the detection of rocks can be either due to your detector's Ground Adjust not being set correctly for the detector to ignore the typical "hot rock," or due to the fact that the rock you just found is truly a positive reading mineral sample. Hot rocks are iron ores or magnetites, which are "negative" with respect to normal ground signals. Their intensities can vary considerably, which makes setting a detector to get rid of all of them a little tricky.

The discrimination circuitry of a motion detector uses two channels of filtered signals to come up with a composite discrimination signal. The normal Discriminate signal is filtered to get rid of ground effects, but the resultant signal has lost its DC reference, and is now an AC signal. The only way to tell if it is good or bad is to filter the All Metal signal in identical circuits and compare its result to that of the discriminator. If both signals are the same, the discriminate target must be good, because an All Metal signal is "inherently good." If they are different, the Discriminate signal must be "bad."

Earlier motion detectors (the 4-filter type), usually beeped at hot rocks, but switching to All Metal yielded a "null" response. Since the hot rock was negative in All Metal, and also negative in Discriminate, both signals were the same, and the detector said "good target," even though it was really bad. Now, most manufacturers set the ground adjust of the detector so that the filtered All Metal signal responds in a positive fashion to hot rocks. Therefore, the signals are different in the composite, so the detector doesn't beep at a negative hot rock.

Minerals come in many different forms and some of them are detectable. Tree roots can also absorb various chemicals and end up being electrically conductive.Sometimes, all you can do is grin and bear it.


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VLF metal detectors are very sensitive to Iron. Can Iron he rejected while gold nuggets are still found?

Iron can be rejected by a VLF discriminator, while still having the ability to detect gold, if the discriminate level is set very low. Doing this, however, means that the tiny pieces of gold may be lost due to the fact that the signals they cause are below the reference level of the electronic detection circuitry of the detector. The best way to hunt for gold is still in the All Metal mode, preferably with a detector designed with the extremely high gain necessary to detect the little bitty pieces.


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How should the Sensitivity control he set to get maximum depth?

As high as possible while still being able to discern the feeble "deep target" signals from the noise or sputtering signals.


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Will metered detectors find coins deeper than non-metered ones?

Adding a meter to any metal detector will generally not enhance its ability to find targets deeper than before. It takes some kind of circuitry to drive the meter, and if that circuitry has more gain than that which drives the speaker, it may be possible to detect deeper with the meter, but virtually all manufacturers realize that if they can get deeper performance, they will also add the extra gain to the audio stage as well.


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My friend uses an old TR discriminator and something he calls "reverse discrimination, " and he usually finds more targets than I do. What is he doing?

While it may be very difficult to find a target using an older TR discriminator in the Discriminate mode, it is very easy to find any target while using the All Metal mode. Reverse discrimination means that you search in All Metal mode until you find a target. Then, since you know where the target is, you place the searchcoil directly over it and switch the detector to the Discriminate mode. Then moving the coil off of the target by sliding it about one or two inches in any direction and listening for the sound change will tell you the type of target, good or bad. The word reverse is used, because if the target is good, the detector will go silent or "null" as it is moved away from the target. If the target is a bad one, the detector will beep as the coil is moved away from the target. This technique can work very effectively for someone who is very patient, but with the technology we have today, it seems to me to be a waste of time.


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How can I overcome interference from other detectors when I am at a treasure hunt?

Interference is caused by two detectors of the same search frequency operating very near each other. The nearer the two frequencies are to each other, the farther away the detectors will "crosstalk." Crystal controlled detectors can be very bad for this interference problem, since the crystals are very accurate. Unless you can get a "frequency shifter box" for your detector, you ,can only get further away from the offending machine. Many metal detectors are manufactured today by various companies using essentially the same frequencies. Tesoro doesn't use the same frequencies as other companies and doesn't use crystals for this very reason.


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Are "audio enhancers" really any good?

They operate by amplifying weak signals and attenuating strong signals. Therefore, they tend to make all signals sound alike. They can be very helpful when your hunting mode is TR Discriminate, All Metal, or if your detector has an "audio threshold." On "Silent Search" detectors, they're not quite as effective. Although one thing they do on silent detectors is limit the sound output in your headphones when you hit a piece of surface trash. This can add to your comfort if you hunt for extended periods of time.


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Explain "Ground Canceling" so that I can understand what it is, and how to adjust my detector to the right point.

Think of Ground Canceling as being exactly the same thing as Discrimination. If your Ground Control is set too low (CCW), the detector will "reject" the ground by going silent as the coil approaches the ground. If the Ground Control is set too high (CW), the detector will "find" the ground by beeping as the coil approaches the ground. What you want to do is to set the Ground Control so that the detector remains neutral to the ground or doesn't see the ground at all. By setting the detector's operating point where it doesn't see the ground, it will detect as deep in the ground as it will in air.

This is accomplished by tuning the- detector to threshold while holding the coil in the air. Then lower the coil to the ground and pay attention to what the threshold does as the coil approaches the ground. If the threshold goes away, the Ground Control needs to be turned in the clockwise direction. If it gets very loud, the Ground Control needs to be turned in the counterclockwise direction. After adjusting the Ground Control, you raise the coil, retune to threshold, and do the same thing over again. When you get it right, the sound will change very little as you lower the coil.


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My detector detects large deep nails and rusty items, even when set to reject pulltabs. Is this normal for my detector type?

Unfortunately, most motion detectors can be fooled by large rusty items, especially if those items are circular. Large rusty iron washers are tough for a motion detector to reject, as well as steel bottle caps. Sweeping the detector faster will help a lot on the steel bottle caps and will help some on the large iron washers. Fortunately, large iron pieces seem to be much "broader" sounding targets in the All Metal mode than good targets which are not magnetic.


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Does the audio tone (frequency) affect the depth of detection? I seem to find deeper objects with a detector with a lower tone. 

The frequency or audio "tone" doesn't have anything to do with the depth capability of your detector, but your ear may be much more capable of hearing the lower tones. A lower tone may be more audible than a higher tone with several times the amplitude. The reverse could also be true.


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How much affect does the moisture of the soil have to do with
detection depth?

For a lot of metallic targets, lying in moist soil causes corrosion, whereby some of the metal will leach out into the soil, causing the target to appear much larger than it really is. When the soil dries out, the corrosion may not affect the detector, which makes the target look like its normal size. Gold doesn't corrode in the ground, and silver doesn't corrode nearly as much as copper brass and bronze. Iron and steel, of course, rust in moist ground, and can cause some really horrendous false signals.


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When building a Target ID detector, is depth sacrificed for accurate Target ID?

Virtually all of the Target ID detectors made can find targets much deeper than they can identify them. Discrimination only requires one reference signal, which yields a positive signal for good targets and a negative one for bad targets. To identify the target requires some very special and complex electronic circuitry, which doesn't have the ability to reach the same depth as a simple discriminator. If manufacturers limited the depth of their ID machines to the depth of the indentifier circuit, they would sell a lot fewer of them.


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Are the "super" or "hot" coils that are advertised any good? Why don't the detector manufacturers make them?

If you look at the ads for those "super coils," you will see that they are usually one inch greater diameter than the standard coil offered with the detector that they fit. Being one inch larger means that they will have marginally better depth for the typical targets. All manufacturers make extra size coils for their detectors. If your detector, for example, came with an 8-inch coil, why buy a 9-inch "super coil," if you can get a 10-inch from the detector's manufacturer? The manufacturer of the detector knows a lot more about making coils for his detectors than the guys who build the "super coils" and they generally sell them for less money.


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When hunting rings, would I find more of them and dig less trash by using the "notch accept" of my detector?

Using the "notch accept" feature would probably mean digging a lot less trash, but you would more than likely also dig a lot fewer rings. Rings cover an extremely wide range of discriminate levels, and if you know the proper level for a PARTICULAR ring you want to find, this can be a good thing. If you just want to dig ANY rings, you are best to not use any notch feature, since many rings are found right in the same discriminate level window as most common pull-tabs.


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How should I adjust my detector's discrimination level to get
maximum depth?

To get maximum depth from your detector, the discriminate level should be set as low as possible. As a target approaches the set discriminate level, its response drops off rapidly until it becomes negative or rejected. The closer the disc level signal gets to the cutoff or rejection point of the target, the smaller the signal received from the target. To get the absolute best depth from your detector if you want to reject pull-tabs, set the disc level control to the point where you get a broken signal from the tabs, rather than no signal at all. This will give you some additional signal on all of the good targets that are left.


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Is a crystal controlled detector more stable and better than one which is not crystal controlled?

It may be more stable, all right, at least from the standpoint that its frequency will not shift. But since a crystal is much more accurate than LC networks, you have a much greater chance of crosstalk with other machines of the same brand or model. An LC network, since there are greater errors in frequency, will have a lot less tendency to crosstalk. And since changing the frequency by 10% doesn't yield any difference at all to the rest of the circuit, it seems like an LC network unit would be more beneficial. Tesoro builds its detectors using four different frequencies and utilizes LC networks to help you avoid crosstalk with other Tesoro detectors.


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How much better is a $1,000 detector versus a $250 detector and
in what ways ?

Typically the $250 detector will have the same depth capability as the $1000 detector, but it will not have all of the features of its more expensive sibling. It probably won't have a meter, nor depth measuring ability, notch capability, or target ID.

It probably won't have surface blanking, multiple discriminate levels, or any of the other assorted bells and whistles that can raise the cost of the basic metal detector. But unless you want those features, and understand that you will consume a lot more batteries by powering them, why pay for them? Some manufacturers may put less gain in their cheaper models, but for the most part, you should expect only less features in the cheaper units.


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What operating frequency is best for finding gold?

The frequency of the older style TR detectors that were "state of the art" about ten or fifteen years ago was in the neighborhood of 100 kHz. The first new VLF detectors operated at about 2 kHz, and while they penetrated deeper, it was more because of how they operated than their frequency. Typically, most VLF detectors made today are operating in the range of 5 to 15 kHz, while gold detectors typically operate at about 20 kHz. The increase in frequency gives a minutely greater response to little tiny bits of gold, but again their increased response to small targets is because they typically have about ten times as much gain as general purpose detectors. Increasing the frequency much above 20 kHz gives a tiny bit more response in air testing, but the detector will lose that increase as soon as a target is laid on the ground.


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Are multi-frequency detectors better than single frequency types?

I have not played with one of the newer multi-frequency types, but I hear they have extremely good depth in some instances. But they have problems in many other instances, such as not being able to discriminate out iron trash at great depths and failure to get good depth while working around electric power lines. Plus, they consume much more battery power. They may be worth the extra cost for some people, but I am not sure yet that simply having more frequencies automatically increases depth.