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Showing content with the highest reputation on 12/05/2018 in Articles

  1. 2 points
    Modern induction balance (VLF) detectors usually can operate in two basic modes. A true detect everything all metal mode or a discrimination mode. Discrimination modes use various filtering methods to help separate desired targets from the trash. The filtering takes away from overall depth and the target identification gets less reliable with depth. In nearly all cases a detector operating in a pure all metal mode will find targets deeper than a unit running in a discrimination mode. It is possible to take a detector running in discrimination mode and set it to accept all targets. You are now running with zero discrimination, and the detector now sounds off on all targets. The problem is that some detector manufacturers are labeling this zero discrimination mode as an "all metal" mode since all metals are being detected. Unfortunately, you have not really turned off the discrimination. A true all metal mode employs no filtering at all, it directly reports a target. In zero discrimination the target is still being filtered, but you are telling the machine to report all filtered targets as good targets. The bad news is you still are losing depth and sensitivity compared to the true all metal modes. Most metal detectors are made for coin detecting, and so most only run in a discrimination mode. You can set them to accept all targets, to run zero discrimination, but these units simply do not have a true all metal mode. All metal detectors designed with serious prospecting in mind have a true all metal mode. The reason is simple. True all metal nearly always hits hard to find targets, either very deep items or very small, better than detectors running in a discrimination mode, even when set to zero discrimination. This is so important to me that I will rarely ever consider purchasing a detector that does not have a true all metal mode. Be careful when buying a new detector that if you want a true all metal mode you do not end up with a detector that really is offering only a zero discrimination mode. One clue is that a detector with a true all metal mode will also have a threshold control to set the audio in the all metal mode to a barely perceptible sound level. Zero discrimination modes are usually what is referred to as "silent search" modes without a threshold sound and therefore no threshold control. It is possible for a detector to run in all metal and discrimination modes at the same time. This is referred to as mixed mode Very cool! I am not sure who first came up with this feature but Nautilus has for a long time offered units that put the all metal signal in one ear of your headphones and the discrimination signal in the other ear. More common are detectors that put the all metal output through the speaker and the discrimination signal on the meter. The White's MXT has the Relic Mode, which is a mixed mode. I wonder how many people use Relic Mode but really do not understand it. Good targets give a high pitched chirp. Junk targets honk depending on where the discrimination knob is set. But there is a third, more subtle audio that indicates a target is there but the detector cannot identify it because it is too deep. This is the all metal signal. The meter will be blank but there will be an audio signal. When nugget detecting, you want to hear these, and dig down until the target id kicks in. I think many people focus so much on the other two audio responses that they ignore the fainter deep all metal signal. It is easy to fall into a habit of just digging only those high pitch targets. Not good. White's V3i Mixed Mode program option The various Fisher F75 and new Gold Bug models have a basic single tone in all metal, but the meter is still active in discrimination mode. So you get the signal, then check the meter. If within range, you will see a target id. If deep, the meter will be blank. It is very similar to the old Compass Gold Scanner Pro, which had a target id meter that functioned while in all metal. The White's V3i has a very powerful programmable stereo mixed mode setting. The DFX also offers mixed mode. The new Garrett AT Gold has a true audio all metal mode while the meter is still working in the discriminate mode. The same thing can be achieved with many detectors by running in all metal mode and then, after a target is acquired, switching over to discriminate mode to check the target. The obvious downside is that this requires lots of switching back and forth, and a mixed mode detector eliminates the switching. The key to mixed mode is simple. Those targets in a good location that are so deep you get no indication on the disc channel are the ones you really want to think about. If the area has produced good finds but is now near to being worked out, these deep signals are the ones anyone running in a normal discrimination mode is going to totally miss. Sure, it could be trash. But really deep targets are often the best, and so digging some of these on occasion can produce some really good finds. I have found from my personal experience that detectors often run smoother and targets are easier to hear in all metal mode. I tend to prefer a detector that has an audio all metal mode coupled with a metered discrimination mode. I just listen for the target, and once I hear it I stop and analyze it with the meter. When in doubt, dig it. Some people prefer to dig only targets that read as probable good targets as they do not like digging junk. I tend to dig anything unless it is almost sure to be junk. In other words, I dig the iffy targets. That means I dig more trash but it also means I make finds others miss. It does depend on how patient I am feeling though, and some days I will just dig those really good targets. Those are getting harder to find these days. The only place mixed mode does not work well is in very trashy locations, especially the units that generate multiple tones. It just gets real noisy. But for many experienced detectorists mixed mode is a sort of secret weapon. Now you know why! ~ Steve Herschbach Copyright © 2010 Herschbach Enterprises
  2. 1 point
    I thought I'd point out a link to the Minelab GP 3500 review I wrote for the September issue of Lost Treasure magazine. They have it on their website (edit Dec 2018 - Lost Treasure magazine is out of business and link is gone) for those of you that may have missed it. One thing I made a point of doing in the article is trying to get people to consider the Minelab GP 3500 as much more than just a "nugget detector". The fact is that it is one of the most powerful metal detectors available today, and can hit coins, jewelry, relics, and yes, nuggets, deeper than most metal detectors. Since it is a pulse induction (PI) detector, it has a relatively limited ability to discriminate targets. That said, by learning the tones the machine puts out and using the iron discrimination circuit you get more ability to read targets than is the case with most PI detectors. I've been experimenting with my GP 3500 as a coin and jewelry detector. The short story is it easily hits targets deeper than the best VLF detectors. Yes, you dig more junk, but the biggest limiting factor may be that the unit is TOO powerful. You can only dig holes so deep in public places, and so many parks and other groomed areas are in effect off-limits to the GP 3500 as digging holes over a foot deep in not an option in many parks. But for beach use and relic or coin detecting in areas where digging extra deep is allowable, the GP 3500 is certain to pull up finds people with VLF machines are leaving behind. The GP 3500 control box is protected with a Coiltek neoprene cover. I have a half-size Minelab battery tied to the side of the unit in its own Minelab battery belt pouch. Another option are the new Pocket Rocket Lithium Ion batteries. The battery is connected to the control box with a Coiltek short power cable, the one Coiltek sells for use as a charging cable instead of using the 3 foot Minelab cable. 6.8 pennyweight gold nugget found with Minelab GP 3500 This setup allows me to set the detector down and dig without being attached to the machine by a normal backpack mounted battery and cable setup. The half-size battery is fine for more hours of coin detecting than I'd normally ever undertake in a day. And the whole setup is not so heavy that I cannot handle it for long hours. I plan to use it for nugget detecting in brushy areas next summer or for some "dig and detect" sessions where the machine spends more time on the ground than on my arm. I'm using the Coiltek 14" mono coil which seems to work well for the coin detecting. The stock 11" coil is ok but is a bit too sensitive to tiny surface trash the larger coil tends to ignore. Being a mono coil the 14" has terrific depth for its size, but I have given up the ability to use the GP iron discrimination circuit. I'm going by the tones only (the review describes this in detail), but I'm looking at a mid-sized DD coil for this use to get back that extra discrimination ability. This would help eliminate a few of the iron targets I'm currently digging. The headphones are the DetectorPro Uniprobe combination headphone/PI pinpointer setup that is a must for this type of detecting. The Uniprobe pinpointers are easily the most powerful I have used, in that they are a full-fledged pulse induction metal detector with a probe attached instead of a coil. In fact, there is an optional 11" coil and handle assembly available to convert the Uniprobe into a great little PI detector. Normally with a GP 3500 you just dig a huge hole while nugget detecting. But for coin and jewelry detecting better pinpointing skills must be developed, and the use of a good pinpointer is a real requirement. I highly recommend the Uniprobe pinpointers. The headphone model is mounted in a set of Gray Ghost headphones, which works great for me as I am a headphone addict. DetectorPro makes a Pocket Uniprobe that has a speaker but I cannot hear it very well with headphones on. Plus, it is just another gadget to carry. I tried the Pocket Uniprobe and decided having it all in one unit works better for me. Minelab GP 3500 rigged up to hunt without using harness and bungee setup The final item in the picture is my digging pick. I do not like the short handles that are standard on most picks. I got a 36" hickory sledge hammer handle and replaced the stock handle, although I can switch it back as both handles mount with a single bolt to the head. I like these long-handle picks as I use them as a walking stick (great for side-hilling at Moore Creek!), and I have to bend over less when I dig. There is, of course, a super magnet attached to the head of the pick for sucking up small iron trash. The only other items I am using that are not in the picture are my nylon belt and large trash/treasure pouch and plastic scoop. The scoop is great for getting deeper into the bottom of the holes I dig, and for locating some small items as would be done in nugget detecting. All trash goes in the pouch for later disposal. I know these detectors are expensive, but if you have a serious need to get some REAL extra depth, you need to look hard at the Minelab GP 3500. These things would be awesome for hunting Civil War relics in a "worked out" location. Goose lake, Alaska plus gold nugget and old coins found with GP 3500 Two last hints. Carry a VLF detector along, and check the targets the GP 3500 finds for you. In some cases the target will be shallow enough you can save a little digging. But better yet, if you get no signal at all from your VLF unit, you'll know you have a deep target. You will be surprised how many of these there are that a VLF unit just will not hit. I afraid once you experience this for awhile you will tend to lose a certain amount of faith in your VLF detector. Yes, you are missing targets. LOTS of them. But the second hint is the best. Take the GP 3500 to a once good place, but one that has been hunted so much that there are no targets left using a VLF detector. I am sure that you will end up like me, simply amazed at how all of the sudden the place seems like it has never had a detector over it, there are so many targets. Better yet, all the shallow stuff should be gone, with only the deepest finds, and therefore some of the best, remaining for you! ~ Steve Herschbach Copyright © 2005 Herschbach Enterprises
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