By Dan Fox
I believe there is not much more they can squeeze out of VLF technology, even multiple frequency has it's limits and is really only 2 frequencies.
Are manufactures better off concentrating on coil design rather than just tweaking an existing design adding a letter or two to the name?
After market coils quite often improve a detectors performance, so shouldn't manufactures be looking in this area rather than using the same coil designed years ago?
Would like your thoughts
By Steve Herschbach
I do what I can to foster competition that develops alternatives to the all too common VLF detector. There are plenty of options out there, but in my opinion they all weigh too much or cost too much. Usually both. I envision people out there with a popular VLF metal detector for beach, relic, or gold detecting. These machines all sell for around $700 and weigh 2.5 - 3.9 lbs. Perhaps they would like to add a ground balancing PI (GBPI) to what they have. I think that for "normal people" with normal budgets a machine under $2K and under four pounds just makes sense. It would be more than twice what they spent for their VLF, and in this day and age there is no reason why a decent PI should weigh over 4 lbs. To clarify what I am talking about here, I should say that for many people a $700 VLF detector is a great place to start and in many cases is all a person ever needs. However, there are places where extreme ground mineralization and mineralized rocks (hot rocks) severely impede the performance and use of VLF detectors. Alternative technology to deal with these conditions has been developed, by far the most familiar being the Minelab ground balancing PI (GBPI) detectors. These differ from common PI detectors by having the ability to ground balance. Other brands have offered the Garrett Infinium (discontinued) plus Garrett ATX and the White's TDI models. These detectors are used not just for gold prospecting but also by relic hunters, beach detectorists, and others who face challenges regarding ground mineralization and VLF detectors. Frankly, in my opinion GBPI technology is largely maxed out. The main room for improvement comes now in better ergonomics at lower prices. This challenge therefore limits detectors to those that weigh under 4 pounds with battery included, and which sell brand new with warranty after discounts for under US$2000. Detectors need not be ground balancing PI models, but must offer similar ability to ignore mineralized ground and hot rocks that trouble VLF detectors. I am going to rate detectors as to their relative performance using what I call the "Minelab Rating Scale. Details here.
1. Minelab SD 2000 - crude first version, very poor on small gold, excellent on large deep gold
2. Minelab SD 2100 - vastly refined version of SD 2000
3. Minelab SD 2200 (all versions) - adds crude iron disc, ground tracking
4. Minelab GP Extreme - adds greatly improved sensitivity to small gold, overall performance boost.
5. Minelab GP 3000 - Refined GP Extreme
6. Minelab GP 3500 - Greatly refined GP 3000, last and best of analog models
7. Minelab GPX 4000 - First digital interface, rock solid threshold
8. Minelab GPX 4500 - Refined GPX 4000, solid performer
9. Minelab GPX 4800 - Released at same time as GPX 5000 as watered down version
10. Minelab GPX 5000 - Culmination of the series, current pinnacle of GBPI prospecting machine technology.
All Minelab models leverage an existing base of over 100 coil options from tiny to huge.
I am a very practical person when it comes to detecting. I know all the existing models and options by all brands very well, perhaps better than almost anyone. This is the way I look at it is this. If I personally were to spend a lot of money to go gold prospecting for one month, and needed a GBPI detector, considering machines past and present, what would I get and in what order of choice? Put aside concerns of age, warranty, etc. just assume functioning detectors.
Here is the issue in a nutshell. On the Minelab scale of one to ten as listed above, I would be generous in rating the White's TDI SL as a 2. Same with the Garrett Infinium which I will mention in passing as it is no longer being made. If I was going to spend a month of my time and a lot of money going on a prospecting trip, I would choose a TDI in any version over the SD 2000. I might go with a TDI Pro over a SD 2100 but I would have to think real hard about that, and when push comes to shove I would go SD 2100 were it not for the realities of age I said to ignore. A newer TDI Pro might be a better bet than a very old SD 2100 from a reliability standpoint, but again, this would be a tough choice. The TDI SL not really. In my opinion I would be shooting myself in the foot to go on this hypothetical trip with a TDI SL instead of a SD 2100.
You see the problem now?
The Garrett ATX fares better. I would rate it a 3, roughly analogous to the SD 2200 variants. Still an agonizing choice really and the ATX being new versus SD 2200 being old might again be the tipping point, but from a pure prospecting options perspective the case can be made that the SD 2200 might be the better way to go. The problem for this challenge is the ATX weighs way over 4 lbs and sells for slightly over $2000. The price is close enough really but the 7 lb weight is way off.
That's it folks. That is reality. The best of the best that the competition can offer can only go solidly up against models Minelab has not made in years. I am not saying that to be mean or as some kind of Minelab toadie, that is my pure unvarnished opinion as a guy who is pretty well versed on the subject.
Let's bring it all home. This person with the $700 machine really, really wants that under 4 lb, under $2K GBPI machine, but if they do their homework they discover that truthfully, they would be better off shopping for a used Minelab than what the competition offers new. With the TDI SL rated as a 2 the ATX in a much lighter box at under $2K is a solid win as a 3. A well designed ATX with standard dry land coils would look very enticing as compared to the GP series Minelabs. But Garrett refuses to budge!
White's can certainly do something, anything to improve the TDI SL. A battery that lasts all day would be a good start. In the end they are limited by the basic single channel design of the machine. The SD 2000 dual channel design was literally the answer to and the improvement on the single channel technology used in the TDI, the basics of which predate the SD 2000. Still, White's currently owns the under 4 lb under $2K GBPI category so they have the first out of the starting gate advantage. Anything they do would at the very least just show they have not given up.
The Minelab MPS patent that formed the basis of the SD series has expired. Not sure about DVT, which formed the basis of the GP series. Where is the competition? What the heck is going on here? Much gnashing of teeth and pulling of hair is going on here, that's what!!!
That is my challenge to the manufacturers. Under 4 lbs, under $2K, on the 1-10 scale I am offering, what is the best you can do?
The TDI SL as a 2? Really? Yes, really, that is currently the best of the best in the brand new ground balancing PI, full warranty, under 4 lb, under $2k category. You can pick up a 3.5 lb TDI SL right now brand new for $1049. The White's TDI SL takes the crown.
Hopefully we will see more competition in this wide open category soon. I have been beating this drum for years to no avail, but I do have reason to believe we are finally going to see more alternatives soon. I hope.
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.
By Steve Herschbach
High Frequency Gold Nugget Detector Roundup
Our cup runneth over!
Just a few years ago the market for "over 30 kHz nugget detectors" was quite limited. For a long time there were only a few options:
Fisher Gold Bug 2 (71 kHz) $764 with one coil
Minelab Eureka Gold (6.4, 20, & 60 kHz) Discontinued $1049 when new with one coil
White's GMZ (50 kHz) Discontinued $499 when new with one coil
White's GMT (48 khz) $729 with one coil
Things were that way for over a decade. Then in 2015 Makro introduced the Gold Racer (56 kHz) $599 with one coil. Sister company Nokta released the AU Gold Finder (56 kHz) $799 with two coils
Then in 2017 we see the Minelab Gold Monster 1000 (45 khz) at $799 with two coils. And although not a dedicated nugget detector, the Deus high frequency coil options (up to 80 kHz) were also released, $1520 for complete detector with one HF coil.
Now in 2018 we get another general purpose machine, the Equinox 800, that can hit 40 khz, $899 with one coil. And just announced...
the Makro Gold Kruzer (61 kHz) $749 with two coils and
the White's Goldmaster 24K (48 khz) $729 with one coil
These last two announcements have made barely a ripple in the prospecting world, or at least going by other forums that seems to be the case. There are various reason for that (forums not being prospecting oriented or being Minelab centric) but still the lack of buzz is interesting. I do believe people are both burned out by all the new introductions and that the market is saturated with high frequency models. Leaving out the general purpose machines to sum up the current options it looks like the current "sweet spot" for pricing is a high frequency model at $749 with two coils. The Gold Bug 2 saw a price reduction to $699.
Makro Gold Racer 56 kHz - $599 one coil
Fisher Gold Bug 2 71 kHz - $699 one coil
White's Goldmaster 24K 48 kHz - $729 one coil
White's GMT 48 khz - $729 one coil
Makro Gold Kruzer 61 kHz - $749 two coils
Minelab Gold Monster 1000 45 kHz - $799 two coils
Nokta AU Gold Finder 56 kHz - $799 two coils
Added 1/2019 XP ORX up to 81 kHz - $899 one coil
High frequency nugget detectors compared
White's Goldmaster 24K, Minelab Equinox 800, Gold Monster 1000, Makro Gold Kruzer
Minelab Gold Monster, Fisher Gold Bug 2, Makro Gold Racer, Nokta Impact
I hooked up a sensor coil to pick up the transmit frequencies from my 800. Connected to an audio spectrum analyzer I could see what was being transmitted in all the modes. Surprise, Park 1 uses only a single frequency ~ 15KHz. The amplitudes shown are relative.