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Varying Height And Azimuth?

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While experimenting with my Gold Racer, I think I saw more stable VIDs by raising the coil and scanning perpendicular to magnetic north. There seemed to be a height that was most stable, and scanning perpendicular to magnetic north tended to eliminate oscillation between very low and very high values.  It wasn't perfect, but it was suggestive.  I'm wondering if anyone else has anything to offer about this.

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Minelab pulse induction detectors in particular are susceptible to directional swing issues but it is not something normally encountered with a VLF. There is a scientific basis for what you are experiencing however.

Metal Detector Basics & Theory by Bruce Candy

See pages 12 and 13 and in particular the section on atmospheric sources of interference.

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    • By Steve Herschbach
      I consider myself to be extremely fortunate due to the fact that the entire age of modern metal detecting has taken place over the course of my lifetime. I was too young in the 60's to be one of the many famous names that were there first on the ground with these new toys that go beep. That's good though for me as most of them are gone now and I'm still here. I got my first detector at the true dawn of the modern detecting age when I got my White's Coinmaster 4 in 1972. It was one of the first of the new "TR" machines that were the starting point for what most of us use today. Mine was as basic as a detector gets, no ground balance existed yet or discrimination. Just a couple inches depth and a beep, dig it up. So I have been involved in detecting now for 47 years. I started my business while in high school in 1976, and have been involved in metal detecting pretty much daily ever since.
      Anyone who followed my online presence starting in 1998 may see a pattern. I have been involved in some top end machines, some VLF, but basically almost every ground balancing PI made has been in my hands at some point. I had a vision in my mind based on my background in computers that told me what was possible and where we were headed.
      I was particularly incensed when an upstart company from Australia showed up the industry leaders at the time with the world's most powerful gold detecting PI machines. All the more so when I heard White's had a shot at it and passed. I made it my mission to jump on and foster anything that came along that might compete, and so I was involved with the Garrett Infinium, the first U.S. ground balancing PI. I had a lot to do with White's finally producing the TDI.
      Yet the fact is nobody ever seriously took Minelab on, and finally they won me over because they delivered when the rest just milked us. Minelab has been the sole company at the forefront of this technology since the SD2000 was introduced.
      All this time I have wanted two things. A vision in my mind of what a VLF could be. And a similar vision regarding a PI. Both those visions basically revolved around something a normal person could use both as regards ergonomics and price, two areas we kept getting bent over on for 20 years.
      Long story short I am grateful to Minelab for allowing me to be involved in the machine that delivered on my first vision. The Minelab Equinox is the first machine ever that really can do any VLF metal detecting task and do it well. In any one area it may not be "the best" but no one machine delivers across the board like the Equinox. My VLF quest is over. I will use an Equinox as my primary unit until a detector comes along, probably a Minelab, that does what it does but better. No more VLF buy and try for me. Yay!
      In 2017 I laid out my vision for the PI I wanted. The price was kind of a set the bar high (with a low price) thing so there is a little wiggle room there. But not a lot... the machine price should be something most people can stomach. As far as I am concerned the GPX 4500 sets the standard at $2699 both for performance and price. The TDI wins on ergonomics but loses too much in performance for me. All I really wanted was a GPX performance in an ergonomic package, and we all know it can be done. That is what is so frustrating. It's one thing to introduce new tech but all I want is proven tech packaged right. Garrett has really been a disappointment not putting the ATX in a light box. They can do it but so far have refused. I would have been satisfied with that.
      Right now I am calling the Australian made QED as being the default winner of my challenge. The rough edges have been smoothed out, and it's got the ergonomics, coil selection, and price all right. I am not going to argue with anyone over performance. Based on what I know it's good enough for me to go find gold and easily beats the TDI and is competitive with GPX. Good enough for me and good job boys. The only niggle is no FCC approval for U.S. sales, no U.S. dealers or service. But by end of 2020 if there is nothing better I will have one anyway.
      But we have the Fisher Impulse AQ on the verge and a dry land prospecting version promised. I would be crazy not to wait and see what develops there. I sold my GPZ for many reasons, mostly because I was not going to be detecting much this year, but I resolved when I sold it I would wait until my vision appeared. I knew it was close. I decided I can have fun enough with Equinox until that happens.
      Put as simply as possible I want a reasonably powerful PI packaged like a good VLF that most of us can afford. Something that can get in and out of a small backpack with an hour of labor being involved.
      So I am tossing down the gauntlet. I have my magic VLF and am looking for a mate for it. Right now QED and Impulse are in the running. And it's up to Minelab, Nokta/Makro, and sure, let's toss Garrett and White's in there also. It's time to deliver as by the end of 2020 I am getting one. I prefer in the spring but if something is one the radar I may wait. By 2021 I will be using something that finally fulfills what this high school kid from Alaska has known would happen someday. And I got to be there and see it all from start to finish. As I said... a very fortunate soul! 

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    • By Steve Herschbach
      From Wikipedia:
      "A long-range locator is a class of fraudulent devices purported to be a type of metal detector, supposedly able to detect a variety of substances, including gold, drugs and explosives; most are said to operate on a principle of resonance with the material being detected."
      There is more at the link, but "a class of fraudulent devices" says it all as far as I am concerned. I just wanted to post this so people can find it in the search results in case they are looking.
      For me these devices have always failed the most basic test... the experience of hundreds of thousands of prospectors and treasure hunters around the world. Treasure hunters and gold prospectors will give anything a try that might work, no matter how crazy it seems. If it works, the use soon spreads to other prospectors. You can Google genuine successful results for regular metal detectors all day long. The internet is full of successful people using normal metal detectors to make great finds. Except for a few obvious promotionals, the success stories of people using LRL devices are glaringly absent. All excuses for why this is so flies in the face of the simple common sense answer - they don't work. In almost 50 years of metal detecting and prospecting I have met a lot of successful people, and none of them got that way by relying on a long range locator.
      Part two of the common sense test is if they did work, there would be at least a few users of these devices that would be fabulously rich. The few I have met are anything but... just the opposite. Again, excuses made about why these rich LRL users are invisible fly in the face of common sense. As if we are not a country that brags about every tiny thing we can think of! The only people getting rich are the people selling these devices. I personally refuse to purchase anything from a company selling long range locators. It says something about the management of the company that makes me prefer to do business elsewhere.
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    • By Steve Herschbach
      VLF metal detector discrimination works well on isolated targets in an air test. The problem is in the field what is reported by the detector is the sum of everything the coil "sees". This means the ground mineralization, the gold nugget (or any other item you are trying to find), other metal under the coil at the same time, and even electrical interference. Sweep speed matters also as does the angle of the item in the ground and the direction from which the coil approaches it. Add it all up, and it is a miracle discrimination works at all, and the reality is it is wrong very often.

      Almost any ground with iron mineralization will cause non-ferrous items to read as ferrous. Usually it is something that happens right on the edge of detection depth. However, the more iron mineralization, the less depth it takes for the item to flip over to ferrous. It does not matter how large the item is either. Small non-ferrous items are more prone to reading ferrous but even very large items will flip in very bad ground. Bury a two ounce nugget deep enough in bad ground, and it will read ferrous. The ground mineralization pulls the VDI numbers down, and the deeper the item is buried, the lower the VDI number gets until it passes into the ferrous range.
      This happens with coins when coin detecting. A person using discrimination is looking for items that read in a certain number range. The problem is that mineralization pulls those numbers lower and then the items reads instead as a trash item, and is left behind.

      The simplified explanation is the detector is seeing a little bit of non-ferrous signal and a lot of ferrous ground signal. The White's GMT is a rare machine that tries to show you this graphically. It will say a target has a 40% chance of being non-ferrous. Most machines have to call it one way or the other and in this example just go ahead and call it ferrous. Which is it? Ferrous? Or 60% chance of being ferrous? Would you dig something if you knew it had a 40% chance of being a nugget?

      A picture says it all. See the one below. This is such a well known thing that White's has for a long time shown it on their simplified VDI (Visual Discrimination Indicator) scale. On most White's 1 through 95 indicates non-ferrous, and the negative numbers -1 through -95 indicate ferrous numbers. Notice how ferrous readings as low as -20 could indicate gold. Yet nearly everyone using any discrimination at all will tune out this range to eliminate finding small ferrous trash.

      This happens on all VLF metal detectors that employ discrimination.



      Good old Ganes Creek, Alaska is a VLF test bed on a massive scale. Tons of ferrous trash is buried intermingled with gold nuggets in tailing piles. The ground is not all that mineralized and VLF detectors work well there. Because the hunting was pay-to-mine competition style a VLF made more sense than digging hundreds of ferrous targets with a PI while your buddy was cherry picking nuggets around you with a VLF.

      The reputation of the White's MXT as a nugget finder was largely built at Ganes Creek, but many other VLF detectors did well. I saw a couple things over and over at Ganes Creek.

      First, we ran detectors in either of two modes. Dual tones with low tone ferrous, high tone non-ferrous was the most popular. Or there were some who ran in all metal mode then analyzed the target VDI once located. I did both.

      In either case you could get two results very often. In my case running a F75 in all metal I would get a target. I would then sweep it and watch the meter VDI numbers. What I learned is if there were five sweeps that said ferrous and just one that read non-ferrous, then dig it.

      Most people are looking for reasons not to dig. Getting five readings ferrous and one non-ferrous, most people would take that to mean a ferrous target. What I found more often than not is that if I could just get the target to read non-ferrous even once, it was worth digging. These were usually items reading borderline anyway. The only stuff relatively safe to walk away from is items that give strong ferrous readings repeatedly.

      With dual tones the same thing applies. If you get five low tones but then get it to bounce high tone even once, better dig it.

      The real proof was the simple kick test. You go along, get a ferrous indication, and kick a couple inches off the surface and bingo! the ferrous item turns non-ferrous. Pretty amazing stuff. Keep in mind folks, this is relatively mild ground!

      What not to do. If you take any detector and tune it to completely ignore ferrous targets, you are in big trouble. The Gold Bug 2 for instance. If you flip to Iron Disc mode iron targets are ignored as if they are not there. Yes, some will click or pop but most simply get ignored. Any detector with a simple knob, like a Tesoro Lobo in disc mode, you can turn up until a small nail will be ignored. Hunting directly set up to reject ferrous is very problematic.

      Now you can find gold doing this. I have and many people have. The problem is as you go along you only get one chance at the target. If you hunt in all metal, you will always get the target, and then you can analyze at your leisure, or just dig it up. In dual tone you will always be alerted to the target, so you can check it again.

      But if you set to reject, and the detector makes a bad call on the first sweep, you pass over the target and never know it was there at all.

      Part of the problem is in targets that you only get partly over on the first pass. For the discrimination to have its best shot, you need to be centered on the target as much as possible to get the strongest signal. An on edge pass will usually be wrong, but if you are alerted you can make multiple sweeps to get centered on target for the best reading.

      Any detector running in disc mode will have a search field that is more limited in extant than that you experience with the detector in true all metal mode. In disc mode you need to be well centered. In all metal, the coil reaches wider and deeper to gather signals. The reason I usually run in all metal is it gives me the best chance of capturing the target, then I can decide what to do with it. Running directly in disc gives you more chance of missing the target entirely.

      Keep in mind these issues vary wildly with the amount and type of iron mineralization in the ground. I saw some ground in Alaska recently that you would not think was very mineralized. No intense red colors, not much in the way of hot rocks. And yet there was something about the iron in the ground that made fairly large nuggets and even .22 shell casings read as ferrous when sitting directly on the ground in plain sight! Very, very scary stuff.

      Now having said all that, there are times I will crank up the disc and eliminate the signals. Sometimes they are overwhelming in number and it is the only way to deal with it. Maybe I am just tired and not in the mood to analyze every target. Maybe time is very limited and I need to do a quick cherry pick run of the ground. There are no absolutes in metal detecting. The main thing is to have the knowledge required to make the best choices you can, to get the best odds for the situation. Hopefully this little article will help. Here is another.
      For more technical detail see Metal Detector Basics and Theory by Bruce Candy / Minelab. An excerpt:
      “In goldfields, discrimination is required only against ferrous targets, without any time constant discrimination, as gold nugget time constants include all values from very long to short.  Unfortunately, X discrimination in goldfields has several major problems:
      Most productive goldfields are extremely mineralised, and thus the soil X signal is extremely large. As was stated earlier, it is only possible to assess the target X signal if this is comparable to, or greater than, the soil signal after filtering. In such extremely mineralised soil, this will only occur when the target signal is also very large which means the target must be close to the metal detector coil. Hence, discrimination in highly mineralised goldfields is only effective for targets buried at shallow depths.
      The discriminator action must be very conservative so that gold nuggets are not falsely discriminated as ferrous targets. Thus, the metal target signal must not only be comparable or merely greater than the soil X signal after filtering, but significantly greater so that there is no doubt whether the metal target is ferrous or not. This further reduces the depths at which targets may be discriminated.”
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    • By Steve Herschbach
      Which metal detectors have the most reliable target ID numbers?
      Target ID is a function of depth - the deeper the target, the more difficult it is to get a clean target ID as the ground signal interferes. Other items directly adjacent to the desired target can also cause inaccurate numbers. The more conductive the item, the higher the resulting ID number, but also the larger the item the higher the number. Silver is more conductive than gold, so a gold item will give a lower number than the same size silver item. But a very large gold item can give a higher number than a small silver item, so numbers do not identify types of metal. Gold and aluminum read the same and vary in size so to dig one you dig the other. Only mass produced items like coins produce numbers that are more or less the same over the years but a zinc penny will read lower than a copper penny due to the change in composition.
      In general iron or ferrous targets produce negative numbers or low numbers. Aluminum, gold, and US nickels produce mid-range numbers. And most other US coins produce high numbers. Other countries coins, like Canadian coins with ferrous content, can read all over the place.
      The scale applied varies according to manufacturer so the number produced by each detector will vary according to the scale used. The 0-100 range for non-ferrous targets is most common but there are others. Minelab employs a dual number system on a 2D scale with thousands of possible numbers, but they are now normalizing the results produced to conform more closely to the linear scale used by other manufacturers.

      Increasing ground mineralization has a huge effect on the ability to get a good target ID. Ground mineralization is nearly always from iron mineralization, and this tends to make weak targets, whether very small targets or very deep targets, misidentify. The target numbers get dragged lower, and many non-ferrous targets will eventually be identified as iron if buried deep enough. Small non-ferrous readings and iron readings actually overlap. That is why any discrimination at all is particularly risky for gold nugget hunters.
      If you want target ID numbers to settle down, lower sensitivity and practice consistent coil control. The target number will often vary depending on how well the target is centered and how fast the coil moves.
      Higher sensitivity settings lead to jumpier numbers as the detectors become less stable at higher levels. The interference from the ground signal increases and interference from outside electrical sources also increases, leading to less stable numbers.
      Higher frequency detectors are inherently more sensitive and are jumpier. So lean lower frequency for more solid results. Multi frequency detectors act like low frequency detectors and tend to have more solid target numbers due to the ability to analyze a target with different frequencies.
      Another issue is the number of target categories, or ID segments, or VDIs, or notches, or bins (all names for the same thing) that a detector offers.
      For instance here are the number of possible target id categories or segments each detector below offers:
      Fisher CZ-3D = 7
      Garrett Ace 250 = 12
      Minelab X-Terra 305 = 12
      Minelab X-Terra 505 = 19
      Minelab X-Terra 705 = 28
      Minelab Equinox = 50
      Fisher F75 (and many other models) = 99
      White's MXT (and many other models) = 190
      Minelab CTX 3030 = 1750
      Fewer target categories means more possible items get lumped together under a single reading, but that the reading is more stable. Many detectors will tell you the difference between a dime and a quarter. The Fisher CZ assumes you want to dig both so puts them under one segment along with most other coins.
      People who use detectors with many target numbers usually just watch the numbers jump around and mentally average the results. Some high end detectors can actually do this averaging for you! But I think there is something to be said for owning a detector that simplifies things and offers less possible numbers to start with. The old Fisher CZ method still appeals to me, especially for coin detecting. So do detectors like the Garrett Ace 250 or Minelab X-Terra 505 for the same reason.
      The problem is that as people strive to dig deeper targets or smaller targets the numbers will always get less reliable. But if you want to have a quiet performing metal detecting with solid, reliable target numbers look more for coin type detectors running at lower frequencies under 10 kHz or at multiple frequencies and possibly consider getting a detector with fewer possible target segments. And with any detector no matter what just back that sensitivity setting off and you will get more reliable target numbers.
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      Detectors often use tones to identify targets and often use far fewer tones than indicated by the possible visual target id numbers. The X-Terra 705 for instance can use 28 tones, one for each segment. However, most people find this too busy, and so simple tone schemes of two, three, or four tones may be selected. I think it is instructive that many people often end up ignoring screen readings and hunting by ear, using just a few tones. This ends up just being an ultra basic target id system much like the simpler units offer. Reality is that most people do not need or care about huge numbers of target numbers. For many just three ranges suffice, low tone for iron, mid tone for most gold items, and high tone for most US coins. The meter could do the same thing, but for marketing purposes more is better and so we get sold on detectors with hundreds of possible target ID numbers. Perhaps this is a digital representation of an old analog meter with its nearly infinite range of response but the reality is we do not need that level of differentiation to make a simple dig or no dig decision.
      Finally, a picture often says it all. Below we have a shot of the White's M6 meter. I like it because the decal below illustrates a lot. You see the possible numerical range of -95 to 95 laid out in the middle. Over it is the simplified iron/gold/silver range. Note the slants where they overlap to indicate the readings really do overlap. Then you get the probable target icons. -95 is noted as "hot rock" because many do read there.

      The M6 can generate 7 tones depending on the target category. I have added red lines to the image to show where these tones sit in relation to the scale. It breaks down as follows:
      -95 = 57 Hz (Very Low) Hot Rock
      -94 to -6 = 128 Hz (Low) Iron Junk
      -5 to 7 = 145 Hz (Med Low) Gold Earrings, Chains - Foil
      8 to 26 = 182 Hz (Medium) Women's Gold Rings/Nickel - Small Pull Tabs
      27 to 49 = 259 Hz (Med Hi) Men's Gold Rings - Large Pull Tabs
      50 to 70 = 411 Hz (High) Zinc Penny/Indian Head Penny - Screw Caps
      71 to 95 = 900 Hz (Very High) Copper Penny/Dime/Quarter/Dollar
      Note that the screen reading of +14 is noted as being a nickel or ring but it can also be the "beaver tail" part of an aluminum pull tab or the aluminum ring that holds an eraser on a pencil, among other things.
      The best book ever written on the subject of discrimination is "Taking A Closer Look At Metal Detector Discrimination" by Robert C. Brockett. It is out of print but if you find a copy grab it, assuming the topic interests you.
      Always remember - when in doubt, dig it out! Your eyes are the best target ID method available.


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