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Great video, though I am not sure Alan's technical explanation is correct. I believe the SDC employs multi period pulse technology. However, Minelab specifically chooses to use timings that ignore mineralization that troubles many prospectors when they designed the SDC 2300, making it immune to most hot rocks. As Alan explains, gold that reads near to where the hot rocks read will have detection issues.

Since the ATX in the video is set to detect those hot rocks it will also detect that gold. The advantage being that in those areas where the hot rocks are lacking the ATX can better detect the gold. In areas where the hot rocks exist and the ATX is tuned to ignore them it will also exhibit weakness in the same gold.

The ATX of course has its own "hole" in that it is unable to detect small gold in highly mineralized ground that the SDC finds with ease. As the video notes, all detectors have their weaknesses. I do believe the ATX has an edge on larger gold, especially in low mineral situations where the ATX can be run after a fresh boot up with minimal ground balance engaged. Put the 15" x 20" mono on the ATX and there is of course no comparison.

Alan Mash is a Garrett dealer who specializes in videos that put Garrett detectors in a good light versus Minelab detectors. He goes by Bearkat on this and most other forums.

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I like this video because it raises an important technical issue that many people are unaware of. I am not a technical wizard, and so what follows is as simple as I can explain it in laymans terms. Reg is better equipped to go into details so hopefully he will show up.

Most PI detectors do not ground balance but because of the way they work they ignore milder ground and salt mineralization, making them a natural for salt water beach detecting. However, if you try and use a beach PI for prospecting you usually discover ground and/or hot rocks that it will have problems with, especially hot rocks.

Eric Foster developed a method of ground balancing for PI detectors that simply subtracts the ground signal from that returned to the operator. Ground balancing can be looked at as just another type of metal detector discrimination. A certain target type is set to be ignored. In this case, the ground signal.

The problem is that gold nuggets vary wildly in size and composition, and for any particular ground reading there are actually gold nuggets that read the same. Because of the wide variety of gold shapes and composition it is almost impossible to say it is a particular size or weight of gold at any particular ground balance setting. All you can know is that at any particular ground balance setting some types of gold may be tuned out along with the ground. That particular type of gold may not even exist where you are detecting, but the fun part is you will not know because you can't detect it!

Bruce Candy saw this early on and developed a PI detector that uses two ground balance channels. This is easily seen on early Minelab models. You take a Minelab SD 2100 and it has a Channel switch. You switch to Channel One and ground balance, then set for Channel Two and ground balance, then set the switch to Both Channels and go detecting. Bruce called this Multi Period Sensing, or MPS technology.

The two ground balance channels are specifically chosen to be offset, so that nuggets ignored in one channel will be picked up in the other. Both channels are looked at and compared, and the strongest signal from either channel is reported to the operator.

The Eric Foster design could be called a Single Channel design, and the Minelabs a Dual Channel design. The White's TDI variants are based on Eric's circuits, and the so-called "hole" can be demonstrated and manipulated with the ground balance control. Targets that fall in at the exact setting as the ground balance can be totally eliminated, and targets very near the ground balance setting will have very poor signals and therefore depth. The TDI at normal ground balance settings has very poor depth on and can possibly eliminate nuggets around the 1/4 oz mark, but as I explained before the size is extremely hard to predict. But it is large and an eye-popper seen in person. In theory in milder ground and knowing what kind of gold to expect the ground balance can be manipulated to help alleviate the issue, but it requires a kind of omniscience most of us lack. The best you can do is manipulate the control to enhance the signal on smaller gold or on larger gold.

There were some early Minelab tricks that involved running on one channel or the other instead of both and you could again purposefully offset the ground balance settings, and again, this is way beyond the skills of most people to get right, and will usually make things worse if you do not know what you are doing. Minelab ended up eliminating the ability to manipulate channels directly and eventually incorporated automatic ground balance methods.

The early Minelab models did better than Eric's design but still had issues in certain ground types and with certain rocks. Minelab experimented with different pulse trains and ground balance settings to come up with a series of "Timings" that could deal with different scenarios. New models added new timings until you get to the GPX 5000 with a rather bewildering number of possible timings to choose from. In general, as the ground mineralization or hot rocks get worse, there is a timing you can chose to help with that situation.

The thing is, as the timings get more aggressive, more possible sizes and types of gold are eliminated along with the ground and/or hot rock that the timing is designed to eliminate. If you chose a timing that is more aggressive than the situation calls for, it can miss nuggets that a more appropriate timing would discover. There is an issue with people running aggressive timings, like the Fine Gold timing, almost all the time because it works well. And it will because it is very aggressive, but it also eliminates certain sizes and types of gold due to that aggressiveness. Running in Fine Gold if you do not need it to deal with the actual ground conditions is not a good idea. In general use the least aggressive timing that will work.

A problem related to that is Minelabs choice of names for the timings, which developed haphazardly over time and is misleading. People think Fine Gold is the best setting for fine (small) gold. Makes sense, right? Well, it is the best for small gold in extremely mineralized ground. In mild ground, Sensitive Extra is superior on small gold.

By developing this range of preset ground methods Minelab ends up making you have to choose which one to use. And using the wrong ones can have consequences. If you have a hot rock that signals and you eliminate that rock, you know you might miss gold also that reads like that rock, and that is an acceptable trade off. But if you use that setting to eliminate a rock, and the rock is not where you are detecting, then eliminating that rock is no longer an acceptable trade off.

The problem is that it is really almost impossible to predict just what gold sizes will be eliminated at any particular setting due to the huge variation in gold sizes, composition, and shape.

The SDC 2300 was designed to be extremely simple to operate and so I believe it uses a variation of the Fine Gold timings, which are intended to extract small gold from extremely mineralized ground. This does mean however that in mild ground the settings may be overly aggressive and eliminate or reduce the signal on certain sizes of gold. It has been said since day one that larger gold is not the design goal or strength of the SDC 2300, although it does quite well on most larger gold.

It appears Garrett has looked at this situation and determined to build a multi channel detector that, rather than use preset timings, attempts to ground balance just to the specific situation at hand. The goal being to only eliminate exactly that ground or hot rocks that need to be eliminated, therefore lessening the risk of choosing an inappropriate setting and possibly missing gold. In low mineral gound in particular I am willing to bet various tests can be contrived to show certain Minelab timings to be exhibiting these weak spots. Again, this is done by choosing a timing that is more aggressive than is called for. In the case of the SDC 2300 however, you get only the choice already hard wired into the detector.

A big issue exists with both the ATX and the SDC 2300 in that they retain the last settings used. That means that is you are in a bad location and ground balance the ATX to a hot rock, turn the detector off, and move to another location, when you turn the detector back on you now have a setting too aggressive for the location and will miss nuggets you should not miss. This also can be easily demonstrated, and it is a good idea to do a system reboot of the ATX when turning on at a new location. This puts the detector in what is basically the most powerful setting possible with minimal ground balance engaged. Then go from there. I have asked if the SDC 2300 has a fresh boot ability but to the best of my current knowledge it does not. Presumably doing a fast ground balance clears and resets the ground balance settings but I do not know exactly the situation there. I will experiment with all this when I get the chance.

The implication is that these "holes" are design flaws when they are in fact artifacts of chosen ground elimination methods. The take away here should be that you should never use more discrimination or more aggressive ground balancing than you need for a particular situation. I have to note that after many campfire discussions on the subject myself and others decided that all detectors miss certain targets. Therefore what is important to focus on is not so much what you are missing, but what you get at the end of the day.

For the Garrett ATX versus SDC 2300 this can come down to this. If the area you are detecting is extremely mineralized and loaded with smaller gold, using the SDC will more easily put that gold in your pocket than using the ATX but you may miss certain classes of larger nuggets, especially those very large nuggets at great depth that a GPX 5000 would easily hit. Conversely, in certain lower mineralization situations that Garrett ATX can be run with almost no ground balance at all and when set like that it is very powerful with impressive capability on a range of sizes. However, if the ground mineralization is low enough a good VLF in all metal mode will exceed the performance of the ATX. So you need enough mineralization to impede the performance of the VLF but not enough to cause the ATX to require more aggressive found balancing. Otherwise you may as well use a VLF.

To sum up when I look at detectors I see a range of performance options that grade almost imperceptibly from one into the other and with a great deal of overlap. Every time I grab a detector I have to decide what I want to trade off in the way of performance. Do I want big nuggets deep, or do I want best performance of the smallest gold? No one detector yet does both perfectly at once. The case can be made I think that the Garrett ATX for the money has a terrific cross board performance on a wide range of nugget sizes. It loses out a bit on the smallest gold compared to the Minelab SDC 2300, and it loses out a bit to the Minelab GPX 5000 on the largest gold at depth. But the Garrett ATX does extremely well on the vast majority of stuff in the middle. I will continue to hope for a Garrett ATX designed specifically for dry country prospectors with standardized coils as it is one of the better prospecting circuits currently available.

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Wow,

I have been reading and "studying up on" PI detectors for more than 7 years now. I carefully read Reg Sniff's short technical paper on how PI's work and "meditated" on it till I understood it. I have owned and used 4 PI detectors by 3 different manufacturers. I have read TONS of stuff on every model of PI detector Minelab has ever produced, studied the extremely confusing timing charts on ML's webpage, written dozens of posts myself on various forums - asking questions - giving my (often ill conceived) opinions.....

Now I read a page or page and a half by Steve and there it all is, wrapped up in a pink bow.

Wow - well done.

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Ha, ha, Rick, thanks! I laugh because I am in a good mood out finding gold, and I just thought "I guess I will go out with my SDC 2300 and miss some middling size gold". Do I worry about the gold I might miss, or be happy about the great specimen gold I have found the last two days? I think I will go with happy!

Have a good one yourself.

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You know the "hole" in PI detectors sounds like an interesting magazine article to me............

 

No fair… Steve already wrote it for you.  :D

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On 10/24/2014 at 5:41 AM, Steve Herschbach said:

Great video, though I am not sure Alan's technical explanation is correct. I believe the SDC employs multi period pulse technology. 

Alan Mash is a Garrett dealer who specializes in videos that put Garrett detectors in a good light versus Minelab detectors. 

Alan mentions the "Hole" in his Part 6 video tests from the 5.35 min mark through to 5.48 min mark and the SDC2300 is a "Single Channel Single Pulse" detector regardless of what Minelab tells you as that is what it is.. 

When I first heard Alan say that I expected that is what Garret had checked and tested the SDC to be.

So who is right and who is wrong, Steve or Alan ? 

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