Question: I have a standard 8.5 inch coil. I am planning to get a bigger 12.5 inch coil. What would be the deference?
Answer: Advantages: 1- With a bigger coil you will save some time because you are sweeping a larger area. 2- For bigger targets only , Depth would be improved by up to 20%. Disadvantages: 1- With a bigger, coil you might miss some small targets like nuggets etc. 2- Pinpointing will be more difficult. 3- If you are using a target I.D. Accuracy will be less. 4- In trashy areas, you might have several targets under the coil. This might confuse your detector.
Question: I want to get a smaller 4 to 5 inch coil for my unit. What difference would it make?
Answer: Advantages: 1- Smaller coils are good for trashy areas. 2- For smaller targets like Gold nuggets, smaller coil is better. 3- You can get into between Rocks and other 'Hard to get places'. Disadvantages:: 1- You will spend more time because your sweeping area is smaller. 2- Detection depth can decrease for bigger targets.
Question: I got a 'Hot Coil' for my detector, Mail Order Dealer claimed that I will achieve a better depth. When I put it on my detector, I did not see any difference. Why?
Answer: So Called "Hot Coils" have no secrets ( If they were better, manufacturer itself would have built them). Not only they will not go deeper than standard factory coil but also are less water resistance. Remember, nothing is as good as the manufacturers' brand coil for your detectors.
Question: I am confused with detector Comparison Charts, My Garrett CX model can be converted to Two-Box machine using a Depth-Multiplier. This is not listed there. Why?
Answer: Detector "Comparison Charts" are "paid charts" by certain dealers, manufacturers and magazines. They are full of errors and misleading information. Garrett, and Tesoro detectors have much more features than what you will find on those charts. If you are really interested in the facts , Please check the manufactureres' Comparison Charts not " the fake ones ". For Fisher and Garrett check their last page of the Catalogs.
Question: I bought my detector based on the article I read in a treasure magazine (from another dealer at full price). But now, I am very unhappy about it. How could it happen? I mean the article?
Answer: Unfortunately, some articles in treasure magazines are paid by certain Manufacturers or dealers. It is sad that you lost the money you paid for the detector and the one that you paid for the magazine as well. However, there are some magizines that are mostly based on research and articles writen by people in hobby for year, I can name "lost treasures" to be one the good ones.
Question: I heard of 'Rom Card locators' and 'Long range locators' that can detect treasure with different Antennas. Do they really work ?
Answer: They will work for the dealers to make $$ but not for you to locate treasures. After purchasing them, you will find this sentence on their warranty card; "If you open the box the warranty will expire", just because they know than nothing is inside but a few capacitors or resistors to fool the people. When you want to return it, they will say; "There is a 20% re-stocking fee". Secondly, You will never be able to locate their manufacturer, there is no address written on the warranty cards, except the dealer's address. You will not even know, if they are made in U.S.A. or China or Canada. That is how their 'business' work.
Question: What is the deference between low and high frequency in Gold detectors?
Answer: Gold nugget detectors usually operate in between 17:w Khz to 71 Khz range. Many people think that the higher frequency is better to have. But it all depends on the soil conditions. Fist of all, we can change a frequency of a gold detector from (for example) 18 Khz to 90 Khz by changing a Crystal or a Capacitor or an inductor. This can cost less than $1 worth of components. I personally like 17 to 20 Khz range detectors for Gold nuggets. Because, If we go higher than that machine would be so sensitive that will die in black sand. Dealers, usually like to sell 40- 71 Khz detectors because they show a very good air test. On my opinion, Air tests are the worst way of showing the performance of a detector especially if the detector is a gold detector, because a good gold detector is for black sand conditions (not air) to operate. If detector is in 50 or higher frequency range, Signal will bounce easily by black sand, because sensitivity is high and machine thinks of black sand as small nuggets. Here is the catch, It is easy to build a detector in any frequency we wish, but it is very hard to control the effect of minerals in higher range, unless our design has some filters or circuits that can eliminate black sand and mineral response. High freq. cannot go deep because of minerals in the soil(signal will be reflected)thefore we will miss big nuggets but in exchange we will get small nuggets just on the surface. If you are moneywise, then, you like the big nuggets, not the tiny ones. With high freq. you will loose depth in mineralized soil, and you will sweep over many nuggets without detecting them. Think of high and low freq. as 'light' and 'radio'. light is high freq. Radio waves are low freq. ( with respect to light). Light cannot pass though most objects and reach the target, but you can still listen to radio in a submarine. That is the defference.
Question: (This is a good question asked by Erwin W. L. , San Jose): Per Charles Garrett's book Modern Metal Detectors , the receiver coil sees a phase shift in the electromagnetic signals reflected off of conductive metal targets. The problem of ground imbalance caused by non-conductive iron mineral is reduced, then, if the phase shifted signal is used for detection.

My first question is: Is the amount of phase shift different for different types of metals (and salt water)? And if so, is this phase difference used for metal ID discrimination? Or, is discrimination based on the analog level of the phase shifted signal, assuming the level correlates with conductivity and that this hierarchy is known? The second question is: I sense that iron can more easily be identified than other metals. It is conductive but also has magnetic properties. Does iron present a unique signal such that it can be detected from other metals, and if so what is the principle?

Answer: Before answering this question we need some Introduction: The operation of metal detectors, in some cases, are similar to those of transformers. If we have a n:m transformer and we connect a voltage generator to primary inductor 'n', the voltage will be introduced in the secondary depending on the n to m ratio. When the secondary inductor has no load, it has a little effect on primary, but if we add any real or imaginary load to the secondary. The current will be allowed to flow and this current flow in the secondary will have an immediate influence on the primary. If we short the circuit in secondary the primary will be shorted too ( If the transformer is ideal). This is similar to the third law of Newton, for any action there is a reaction equal and opposite to it. Another example; On short-wave radio, sometimes we can observe a shift in frequency. In reality there are two type of signals received from a short-wave radio transmitter ( to the receiver), 1- the one which is reflected by ionosphere, 2- the one that is produced by ionosphere.

On the other hand a magnet, itself attracts ferrous metals like iron, but it does not do any good on copper. We can never produce magnetic field by copper unless we draw some current through it.

Metal detectors also behave in the same way. The secondary electromagnetic field generated in the target ( ref. to eddy current) effects the signal. The difference between a magnetic field and an electromagnetic field is that we have both electric and magnetic fields (in the second one) traveling perpendicular to each other. Electromagnetic waves are the same as radio waves. In metal detectors radio waves are around 20 Khz, it means that they have wave length of 15 km. Medium wave is around 200m to 1Km and short-wave around 200 m to 10 meter, VHF and FM around 1 to 3 meter and Radar Penetration systems usually around less that 30 Cm. But all are the same called Radio Waves.They are all the same electromagnetic waves but can behave differently in different environments. For example Long Wave travels in ground better than air. that is why they use them in submarines or ships they can not be reflected easily. On the contrary, very high frequencies (very short waves) are used in radar system because they can be reflected easily. (end Introduction)

Answer to the first part: The amount of phase shift is different for different metals, and for salt too. Because if salt is dry, it has very little effect. but when it is wet, Na+ ion is introduced, Na (Sodium) is a metal. All minerals behave the same way , H2O ionizes them and they become conductive and behave like ionosphere for short-wave radios. All ions + can conduct electricity to a degree.

Both phase shift and strength of the signal (analog value or amplitude) are used along with a microprocessor to identify the target. Conductivity of metal plays a bigger roll. Microprocessor in Garrett detectors uses the conductivity of the target to identify it. That is why if the metallic target is big like a soda can, it shows it as a dollar coin because conductivity is great in a bigger objects because of area and volume involved; Sigma (conductivity)= 1/Resistivity and resistivity is ro times length over area, therefore the larger the area is, less the resistivity is, and better the conductivity is.

Answer to the second part: It is not iron itself but the oxides like Fe2O3 or Fe3O4 that help the signal to boost. You have heard from magazines that if treasure is buried for long time, it can be detected easier. This statement is right and wrong, If the treasure is IRON, then it is right ,because Iron Oxides will be released and the target will look bigger for the Detector, but if Treasure is Gold , (Gold does not have any oxides) even if it is buried for a million year, the detection depth will not improve a single inch.

  • Go to Page 2
  • Go to Articles' Menu


  • Back to DetectionNet Main Page


    • Maintainer: DetectionNet, Email.
    All Rights Reserved.
    © Copyright 1996 A&S Company