ARE MINELAB PI'S SUPERIOR?


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Hi Inhere,

When I field tested the SD 2200, I did quite a bit of testing to try to see just what depth difference I could see between the VLF's I was using and the SD. I normally used an 1800 and the SD for comparison during those tests. Now, most of the gold I have found here in the US is 1/4 oz or less, so I concentrated on those sizes of gold when I was doing the testing. At the time I wasn't aware of the "hole" problem with ML's, so that could have influenced the depth capabilities on the particular 1/4 oz nugget I used.

Anyway, I never really did see that much of a depth difference between the two detectors on the size of nuggets I used for testing.

Later, I ran similar tests using my dad's 2100 and had very similar results.

Now, I could easily influence the VLF depth of detection on different nuggets but not the PI's. I could get pretty sloppy and toss most anything at the PI test and still get decent depth. I even found something found in the field that would or could enhance the depth a little on the PI. This helped me to believe one might do better or get better depth under certain conditions. I always meant to follow up on that particular testing but never did. I did pass the concept past a couple of the design experts and they indicated that it was quite possible. If I remember correctly, one of them indicated they had determined the same thing.

Personally, I never saw anything that approached a depth difference of 30% or more.

Reg

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Hi Rob,

Sorry if you took my statement "You are right, why should a VLF owner or one who owns a different PI come back when he finds little help or deals with smart ass remarks." personally. It was not aimed at you. In fact, going back over previous posts, you do a fair job of trying to direct people to what might fit their budget and needs.

The point I think George was trying to make and what I was agreeing to is if a VLF owner or one who can only afford or prefers a VLF asks a question on this forum or most of the other gold prospecting forums, will they get a constructive answer pertaining to the particular detector they have asked about, or will they most likely get responses that tell them to buy a PI rather than focus on trying to point out more about the VLF's in his price range?

Now, over the last few years, I have seen so many of the posts try to steer people to the PI's that I just avoid the posts all together. I think that is what George has seen also, but I can't speak for him.

Again, I apologize if you took the statement personally. It was not meant to be directed at you.

Reg

I have to totally agree with Reg above. My post was simply not directed at you. The above issues are real as I correspond with a lot of other people on other forums.

In fact you and Bill have always been gracious hosts when I posted information about my minority detector on your forums. I don't subscribe to the viewpoint that Minelab dealers opinions should be looked at with suspicion as a wealth of knowledge and information can be gleaned from their experience. If I have issues it is with brand loyalists.

Happy Hunting

George

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Hi John,

Sorry I missed your first post about your purchase of the Hammerhead. I would build the thru the hole unit first. It will take less soldering skill to build. Trying to hand solder SMT devices can be a real challenge. Now, I do recommend you make the mods necessary so you can use DD coils.

Now, in answer to your question about Eric and how he makes his detectors, I am not sure just what all is involved. I suspect he does most of the work and final assembly.

As for the interference problems, Eric's design is clearly superior. Most low frequency noise is canceled so noises such as signals from power lines and even wind generated low frequency noise is canceled. So, his design will run quiet in areas that give the ML's fits.

BTW, the HH you are about to build uses a similar design so you will be able to use it under power lines also.

I would like to help you with your question about the Eureka, the Lobo and the GB 2. I have used and still own the LST (Lobo Supertrac), the original Lobo, the GB 2, but do not own nor have I tried the Eureka. I do still own an 18000 which is the basic unit built before the Eureka. Now, to the best of my knowledge, there really isn't that much difference between the Eureka and the older 18000. As for comparing all three of the VLF's I own, I would hate to say which one is the best. Each has its place.

As for placing one in the hands of an inexperienced person, I would be inclined to give them the 18000 first, then the LST.

BTW, the LST has about the best discrimination of small iron of the three and does so in the all metal mode. The trick is knowing how to set it up and what to do.

Reg

Hi Reg, no problem and thanks for the opinion on the VLF models I mentioned. Building the SMT PCB on the HH is no big deal Reg, that is what I work with at my job. I work with instrumentation used to detect and measure radiation(Geiger Counters and such). Ok I will be watching this thread. God Bless ya Reg and many thanks!

John Tomlinson,CET

John's Detectors

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"Reno Chris - you wouldn't beat me cause I dig all targets. If that meant working that area for weeks I would do it. If I find a spot that seems to be productive I will dig all likely targets".

Ah, that may well be, but also it might be why one would lose with limited time, since the PI does require that all targets be dug.

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Reg:

It sounds like your friend needs to either get his detector fixed or learn how to use it

Now if I were Doug I’d be quite indignant about your insults to my friend, but it suffices to say that he has pounds of gold which he has recovered with his GBII, so for you to just write his experience off assuming he is some kind of newbie with a broken detector is just silly. If you ignore all data that disagrees with you, its possible to prove anything!

Personally, I think all prospectors ought to listen closely to your comments and not waste the money to buy a PI. Heck, if they don’t detect any deeper than PI’s in all types of soil, then why waste the money to buy a PI? Personally I think all new prospectors ought to buy only VLFs and all prospectors who own a PI ought to sell it and buy a VLF. There is a competitive element to detecting, and I would prefer it if all my competition were handicapped!

I’ll leave it with this – If soil mineralization does not affect depth of detection, apparently you know something that White’s Electronics does not, because the following quote is taken directly from their web pages in the discussion of factors affecting the depth of detection for their VLFs:

“The higher the soil mineralization, i.e. the presence of magnetic and/or conductive properties, the more difficult it is for a metal detector to cancel the interference these soils produce. Detection depth is reduced in severe grounds. Depth may increase or decrease with subtle changes in the soil conditions, more noticeably with the entry level models. Soil mineralization varies widely around the country & around the world.â€

Doug:

You are right that one could set up conditions with a tiny nugget, High iron content soil and a long pulse where the current where the current eddy in the nugget would disappear before the magnetic response of the soil did. This is because the tiny nugget reaches saturation quickly where as the total iron in the soil surface under the coil is much larger and continues to absorb energy for most if not all of the pulse period.

The point however, remains that when the timing of the pulse and pause period are well planned, the pause period of the PI allows a large portion of the iron response in the soil to decay away. This is why PI detectors are less sensitive to soil mineralzation that VLFs as a rule. Its not that PIs never have problems with soil iron or hot rocks – they are not perfect, but the PI technology is inherently able to ignore the soil mineralization better than VLFs. Even if both the nugget and soil iron are responding during the first sampling period, you still have a better S/N ratio than you would if there were no time of pausing for the PI.

Rex:

I like Robs comments:

"Reno Chris - you wouldn't beat me cause I dig all targets. If that meant working that area for weeks I would do it. If I find a spot that seems to be productive I will dig all likely targets".

I can only say there is plenty of detectable gold in Lynx Creek and its tributaries. Hows come you see so few Minelab detectors working there? Not for lack of gold, but for excess of trash. There are plenty of similar places in the Mother lode. Rob - tell us about Gaines Creek and how come no one like to use a Minelab PIs up there? After all there is deep gold and you have room to swing a large coil there. Hows come no one likes to "dig it all" there? The answer is that digging deep trash hole after hole just sucks. I know, I own a minelab PI. Believe me, I use my minelab PI much more than my VLF for prospecting, but both have strengths and weaknesses and each does have its place.

Chris

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Hi All,

I noticed that the ProspectinginOz forum has mentioned this thread and, hopefully, may draw a few responses. So, I am hoping, some of the guys over there can fill in some blanks about a test that occurred over there quite some time back. It was a test run by Finders, I believe.

If I am not mistaken, it was those tests that caused Finders to get into trouble with ML. From what I can remember and I hope anyone from OZ who notices what I say to be wrong will jump in and correct it, I remember something about a comparison of one of the latest models of ML (at that time) and how it compared to the previous model and also how it compared to some VLF's. The targets, were buried lead objects, I believe. Now I don't remember all the details, but I do remember that one of the VLF's actually did better than the latest ML in detecting several of the lead targets. I think, overall, one VLF, a Whites I believe, actually did better and could detect more lead objects deeper than the the latest ML version at that time, and that caused quite a stir.

I believe this test was posted on Fnders for some time. Anybody else remember this test and have more details?

Now, lead or a lead alloy objects have been used for years as a substitute for gold when testing different detectors. A quick test with a lead slug such as a 38 slug and a similar size piece of gold will not show that much difference in depth of detection. There may be more of a difference once we get down to pieces maybe 1/2 the size of a 22 cal bullet or smaller because of the lower conductivity of the lead, but overall, lead does work well to test a detector.

Now, the reason I brought up this particular test is tests have been run in many places around the word and many of those tests do not show a really dramatic difference in depth of detection between a VLF and a PI. What will determine the differences are the actual ground conditions and the type of target being used as a test target.

Reg

G'day Reg,

I have a copy of that test you speak of which I could scan and post here on this forum if you wish ?

GaryQ

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Hi Chris,

Jeez, you are trying to sweet talk me aren't you????

Now, I stated the following "Personally, I doubt that he even passed his coil over that nugget even though he went through the area." Once again, that is what I feel happened. That is not insulting your friend in my opinion. I am sorry you took it that way.

If he is a good hunter as you say, than that is what happened. If you chose to ignore that part of my statement, then you are the one missing the point. If he did pass over the nugget and did not hear it, then his detector is either defective or he did have it adjusted improperly for the conditions at that time. His detector should have detected that nugget.

Now, once again I will say it is very easy to have a VLF adjusted so the depth of detection can be hampered severely.

Now, as to your statement "I’ll leave it with this – If soil mineralization does not affect depth of detection, apparently you know something that White’s Electronics does not, because the following quote is taken directly from their web pages in the discussion of factors affecting the depth of detection for their VLFs:"

Now, Chris, where in the world did you get the idea that I said mineralization didn't affect a VLF? Where did I say it didn't affect the depth of detection? If you take time to read my posts again you will find I never said that.

I have repeatably stated the depth of detection is easily influenced on a VLF by certain ground conditions. The trick is to know how to minimize those problems, and yes, it can be done. No, it will not eliminate them, but it will help dramatically.

Lets see what I have said in the previous posts;

"Now, I could easily influence the VLF depth of detection on different nuggets"

"Now, it is much easier to influence the VLF detection depths and just how that happens is the point I am trying to get across. If improperly adjusted, a VLF can display serious depth loss in certain cases and under certain conditions"

"Hotrocks are killers on VLF's. Under these two conditions, the PI really excels and can detect gold that can easily be missed by a VLF. In such areas, the PI can easily beat the VLF for depth"

"Now, what I have seen in the past, is people have a much more difficult time adjusting the VLF and end up with a less than desirable setup. Under such conditions the PI will display a clear advantage."

Then I alluded to what is happening and how I can display what happens. Here is an example of what I stated.

"BTW, I have given several demonstrations over the years and one fun trick is to show just how easy it is to miss a large nugget with a VLF. It really is easy if you know how to do it. I used to show how a 1/4 oz nugget could easily be ignored."

On this test, I would take a 1/4 oz nugget and first pass the coil over the nugget while raising the coil to show how easily the detector can detect the gold. Normally, I can raise the coil 8" to 10" easily and still get a decent signal.

Then I will take a specific rock which is generally in the diameter of a quarter to 50 cent piece and pass the coil over the rock at various distances and let people hear the lack of signal.

Then I will set the same 1/4 oz nugget on the rock and pass the coil over the rock and nugget combination maybe 3" to 5" above. Now, during this part of the test the nugget will be sitting on top of the rock in clear view and facing the coil and the VLF detector will simply ignore the nugget.

Finally, I would adjust the detector again and show how I could once again detect the nugget and rock combination at the distance or very near the distance I could detect the nugget by itself. If I really wanted to cheat, I could actually detect the combination just a little farther, but not much.

This little demonstration is what I use to show how an improper adjustment of a VLF can severely hamper the depth or even the detection of gold objects.

So, Chris, I am sorry you fail to read my posts as they are intended to be read and appear to be taking my statements personally. That is not the issue. What is the issue is the fact that people, regardless of how long they have been detecting or how much gold they have found, have a tendency to adjust the detector such that gold is easily missed. In most cases, they do not know why? That is the point I am trying to make.

The problem is not something that stands out and kicks people in the knees. In fact, it is very elusive if you are not looking for it.

Years ago, I had a guy approach me with a Tesoro and ask if his detector was a good one for gold hunting. I told him it would do a very good job if adjusted properly and that was the trick. I then showed him how easily it was to miss a large metal object by taking my detector, searching around a few feet until I found the right granite rock and then placed a large lead slug (maybe a 38 slug) next to the rock and asked him to pass his detector over it. When he did, he didn't get a signal. He panicked since he could clearly see the piece of lead.

Now this little demo happened on Rich Hill where granite boulders are very common. No, not all of the rocks will cause this problem, but many will and it did happen on every VLF I have ever used. The influence may be more pronounced on some than others.

The point being with a simple adjustment I could change the depth of detection of a metal object several inches on the same object. So, the bad ground would still allow me to detect nuggets deep if I had the detector set correctly. If I didn't, I could easily miss even the shallow targets under the right conditions.

Was the problem bad ground? Nope, bad rocks. Now, when such rocks are common, then it can easily appear to be bad ground. Compensate for them and the detector gets a little noisier but the depth of detection will increase.

As for the statement by Whites, I can certainly understand why it was written the way it was. I have tried to beat around the bush as to why VLF's can easily lose depth and the most I have done is apparently upset people. If Whites had tried to explain just what was happening, most people would panic and quit detecting.

Reg

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Hi Gary,

It has been a very long time since I last saw the test run by Finders. Did the test display what I remember or is my memory fading? I would appreciate seeing a copy of it again, so if you could scan it and post it, I would appreciate it. I would like to look at it again to see if I remember it correctly.

Thanks,

Reg

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Reg:

Doug:

"You are right that one could set up conditions with a tiny nugget, High iron content soil and a long pulse where the current where the current eddy in the nugget would disappear before the magnetic response of the soil did. This is because the tiny nugget reaches saturation quickly where as the total iron in the soil surface under the coil is much larger and continues to absorb energy for most if not all of the pulse period.

The point however, remains that when the timing of the pulse and pause period are well planned, the pause period of the PI allows a large portion of the iron response in the soil to decay away. This is why PI detectors are less sensitive to soil mineralzation that VLFs as a rule. Its not that PIs never have problems with soil iron or hot rocks – they are not perfect, but the PI technology is inherently able to ignore the soil mineralization better than VLFs. Even if both the nugget and soil iron are responding during the first sampling period, you still have a better S/N ratio than you would if there were no time of pausing for the PI. "

But Chris what about the situation where the Tc of the target is longer than the pulse length? At least at very early times after pulse termination (where you must sample to detect small nuggets) there will always be ground signal present and it may be of very high amplitude. In the case of ML the longer pulse is about 260 usecs so in ground with large amounts of ferro/ferri magnetic minerals particularly those containing super paramagnetic sized grains the ground signal or magnetic lag may persist for at least this pulse length as grains return at variable rates to their ground state orientation. The ground signal may also persist for longer if the ground contains conductive minerals. So as far as Pi goes its how the well detector removes the ground signal component in the early time sampling window(without significantly reducing the target signal component) over particular types of ground that really determines the depth and sensitivity and is also critically dependent on the S/N which is really perhaps the ultimate determinant of target sensitivity and depth.

But you are correct in saying that the one key difference between VLF and Pi is the ability to null out the ground signal components. VLF machine’s tend to be adversely effected by both magnetite and maghemite, Pi machine's are largely unaffected by the former but are affected by the latter and hence the need for a GB circuit. Reg has also mentioned how in VLF machines the depth of detection is very significantly affected by how the vlf is set up. Now here is a trick from oz just to show how true Regs statement is. In the early Garret days we had some ground in Oz where it was almost impossible to detect unless you raised the coil say 5" above the ground.the depth of detection was very poor. But what we did was to tape some hot rocks or the soils that were causing the problems to our coils! This reduced the ground noise a lot and enabled us to get our coils much closer to the ground and perhaps nearly double our depth! Another very interesting question concerning transmit field strength is ground magnetic hysteresis. Candy claim's that he uses DVT in the ML gp to prevent saturation magnetization of ground ferrites (or induced polarization?) presumably because he has evidence that the long Tx pulse at full coil current will cause magnetic staturation. Assuming this is correct ( many other people have not shown this effect) then does it apply to VLF machines as well if we assume that their transmit field stengths are less than for Pi machines? If not then VLf machines may by virtue of not inducing magnetic saturation have some advantages over Pi machines?

The other thing that has not been mentioned is transmit field strength of Pi's vs VLF. I suspect that the transmit field strength of a Pi is larger than a VLF when you consider that the back emf from pulse termination in a Pi can be greater than 100 volts and peak coil currents may reach several amps. The depth of detection is certainly a function of coil magnetic moment = Coil area x coil current x number turns of wire in the coil. So an increased coil current in a Pi at pulse termination will with a coil of the same size and number of turns etc as a VLF gives a higher magnetic moment or field strength. However the effect is as Reg has pointed out is not dramatic; to get a 10% increase in depth you will need to double the coil current and to get a 100% increase in depth you would need to increase the coil current about 40 fold!

Hence Regs skepticism about ML machines going 3-4 fold deeper than VLF machines.

I have the same opinion when someone tests the 4000 and says that it goes 18% deeper than its predecessors or some of the other extraordinary depth claims being made (like on a new oz forum 12 grams at 27†in oz soils!!!)

The other matter that many folk fail to understand is the implication of the laws of EM. A magnetic field falls off by the cube of the distance. This means that a nugget recieve signal at 20†will be 1/64 as strong (2x2x2 for transmit x 2x2x2 for receive =1/64) as a nugget signal at 10†and 1/4096 strong at 40â€!

There is no doubt that Pi machines go deeper than VLF machines in magnetic and mineralized soils ( due to their ability to null out the ground signal and hence have a better S/N), but do they go up to 400% deeper, I doubt it! I don’t know how much deeper Pi’s go compared to VLF’s over a range of soil types but I would very surprised if it was much more that 20% at best which can of course make all the difference between detecting a nugget and not detecting it. I think VLF technology still has along way to go and future developments may surprise us.

Doug

http://groups.yahoo.com/group/ProspectinginOz/

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Hi everyone, I was thinking about auto ground tracking. I have heard that a lot of the proffessional nugget hunters prefer the SD2100 over the other machines with auto ground tracking so that they have more control over the machine. If this is true it leads me to wonder how good is auto ground tracking? Is it really very reliable? Also does the auto ground tracking on PI's perform much better than VLF detectors? It seems to me that getting a detector ground balanced is the easy part, but getting it to keep up with the constant changes in the soils is another story. Just wondering. Thanks.

John Tomlinson,CET

John's Detectors

By the way I had a short email exchange with Bruce Candy and he said the next 10 years hold many wonderful things for metal detector technology.

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Getting Gold nuggets with a detector, is 90% operator, 10% detector. My opion. I have gotten just as much if not more in a certain area, where PI's were being used, I was using a VLF. But! And thats the Big factor. I knew my detector and used it like it was part of me. Now I have PI's and do the same thing. I still think its the operator. Grubstake

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Hello All,

Reg Sniff should know by now, if I egg him on enough about the PI's he will post very informative information about detectors. :D

However, I have one question .... "If my Minelab PI would find a small nugget at 4 inches deep and a VLF could only hear the same nugget at 2 inches, wouldn't that be 2 times the depth? :huh:

Minelab did make the claims that the PI's were getting 2-3 times the depth over conventional VLF detectors. They also stated the GP Extreme was getting 55% better depth on small nuggets and 18% better depth on larger nuggets over the SD series.

I would agree in mineralized ground that the Minelab PI's are getting twice the depth.

Talk with you later,

Rob Allison

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To me running a detector is like a blind man making love to a woman that he has just got in bed for the first time, you have to feel it, run your hands over it, try different setting, what works well for one person may not work well for you, find you own hot zone. I have seen many times, guys I hunt with, miss nuggets, because they go too fast, too slow or just don't hear them, As Shep has proven, he found a 1/2 oz nugget in an area that has at least 6 different people go over, He just had the right settings and took his time and found that missed nugget. Was it a different coil? No not really I had used the same coil on the area, was it his new 4000, maybe. but the nugget was only inches deep, one that big would have gone off on a radioshack detector. There are many things that can make you miss a nugget, or find one. I don't think it comes down to just the detector, its only a tool. What do you all think? Grubstake

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Hi everyone, I was thinking about auto ground tracking. I have heard that a lot of the proffessional nugget hunters prefer the SD2100 over the other machines with auto ground tracking so that they have more control over the machine. If this is true it leads me to wonder how good is auto ground tracking? Is it really very reliable? Also does the auto ground tracking on PI's perform much better than VLF detectors? It seems to me that getting a detector ground balanced is the easy part, but getting it to keep up with the constant changes in the soils is another story. Just wondering. Thanks.

John Tomlinson,CET

John's Detectors

By the way I had a short email exchange with Bruce Candy and he said the next 10 years hold many wonderful things for metal detector technology.

G'day Wirechief,

All the Minelab PI auto ground balance detectors have no trouble ground balancing in the gold fields, in my view.

Of couse the later GP's are better. But they all do a great job. The only VLF's i've tried are the ML17000 and the ML18000, In my view, they are not even nearly as good at auto ground balance.

The best guy I know uses a SD2100, great machine. <_<

My score: Minelab PI's 95%

Sundry VLF's 5% :lol::lol::lol:

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Hello everyone, 29prospector here. I have been following this thread with much interest. I've hardrocked most of my life at least up to 1999, moved to dry placer and in 2006 started working with metal detectors. I use a GB2 and have had the chance to use a GP Extreme. Most of the tech. stuff I understand somewhat, but I have to agree with Grubstake, operator is 90-95% of the finding. I have an area that I have gone over 5 maybe 6 times and each time I find nuggets. Are they big? Well I weigh in DWT and they all fall from 1/4dwt to 1.8dwt. I have seen PI's used in the same area and one 1 nugget found. As I watch people, because I think the best way to learn is to watch and listen, I have found that many with VLF's and PI's move fast like they have to cover X amount of ground in a day. I personally think maybe slowing down and taking your time to listen to what your machine is tell you is the first key to seccuess. Yet I'm very new at this, but so far this is what I've learned.

O'29 in 29

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Hello Doug,

When the Minelab GP Extreme first came out it was on the brochures and in the magazines. The ad stated the Extreme was getting 55% better depth on smaller nuggets and 18% on larger nuggets at depth. I believe I still have a copy of the ad somewhere, might be on my old PC though.

Hope this helps a bit,

Rob Allison

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I remember Jack Lange saying the 18% extra depth, related to detecting on salt lakes, Guess they just forgot to put that in the adds. :lol::lol:

I'd go close to believing the 55% on the small bits, but. I well remember going down to Wedderburn to buy the Extreme, wandering around on the outskirts of Queens gully and other places and picking up bits while I was trying the thing out.

I went back 12 months later and the bits were as rare as rocking horse crap. The Extreme's had sure cleaned up the most of the small gold around there..

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Hello All,

Well, it is about time to summarize some of the items I have mentioned in previous posts in this thread. Hopefully, those interested will pick up a few tips. If you do not believe what I have to say, my recommendation is to just pass on this post.

Now, to begin with, much of what I will write is not my "self taught" knowledge but information I obtained from some of the more noted people involved in the design of VLF's When I had my technical column at Lost Treasure, if I was presented a question I had no answer for, I was very fortunate to be able to pick up the phone and call people like George Payne. He was alway willing to put forth a technical response that made sense and answered the question. I also relied on information from Jack Gifford, especially when Tesoro's were involved. I was even fortunate enough to have a few conversations with John Earl, who, at the time was with Compass. All were more than cooperative in assisting with answers.

I always figured those who designed the detectors would know best.

I would always follow up with a series of tests to see or verify what would happen and how I could minimize a problem.

Ok, one of the questions I mentioned earlier had to do with a statement about ground balancing and which was better, ground balancing to the ground or with a positive setting. I also mentioned that both answers are correct. What determines which is correct is the number of hotrocks in the area or the general ground makeup. If the area is basically open clay type ground with very few "negative" responding hotrocks, then the best setting generally is to ground balance to the ground. This allows one to hear the faintest signals much easier. This is what most autmatic ground balances units will try to do.

Now, get into an area where there are rocks that generate even a slight negative response and one really should adjust the ground balance such that these rocks are nulled or respond with just a slightly positive response. This will make the ground a little noisier but will also assure few nuggets are missed.

The reason for this is because the signal strength of ferrite is, according to Candy, is significantly greater than the signal from a non ferrous object. I believe the figure used was 40 times stronger, but I can't be absolutely sure. I have it written down somewhere but at this time, I don't remember where. Regardless, whether the difference is 40 times, 30 times, or even 50 times, the ferrite signal is much much stronger than the metal signal, so even the slightest negative response can easily cause a metal object to be ignored.

Now, we generally think of black sand or magnetite rocks when we think of ferrite signals found in the field, but this same stuff can be found in many of the granite boulders and the quantity is such it can easily mask a large nugget. To be honest, it doesn't take a rock of any size to be a big problem. In fact, when you get into areas with a lot of gravel, one has to be very careful and adjust the detector accordingly since even small gravel containing magnetite can severely reduce the depth of detection and in the case of small nuggets, can cause them to be ignored. In other words, the depth of detection in areas where magnetite in rock form is signficant and it is easy to reduce the depth capabilities to almost nothing and not even know it.

Solid concentrations of black sand are bad by themselves because they will make it almost impossible to be agle to keep the threshold constant. About the only way to deal with that stuff is to simply raise the coil a few inches..

For those of you who have followed this thread, you know I mentioned taking a 38 slug placing next to a granite rock and could pass the coil over the slug with a few inches between the coil and the slug and not get a peep from the piece of lead. The reason was because the granite rock had enough magnetite in its composition that the rock would generate a negative response, and this response was stronger than the response from the slug.

Before going much farther, I probably should explain what I mean by a negative response. Most VLF's designed for gold hunting have a relatively fast autotune circuit. One can also adjust the threshold for a slight audio response. Well, if we ground balance to the general ground and then pass over a rock having sufficient magnetite, the threshold will reduce and generally go silent which will then be followed by a positive "boing" once the coil has passed the rock. If this type of signal is happening, it is a negative response, and such responses will easily mask a nugget signal hidden under the rock or even right up against the rock. Instead, you will simply hear the detector go silent and the usual boing.

This ability to ignore gold is easy to do because the signal from gold is no where as strong as from iron or ferrite of similar size. Now, to test for this is an easy test to do. All it takes is a nugget or lead if you do not have a nugget to use and a hotrock of sorts. A piece of magnetite is the best, but even many of the granite boulders found around Rich Hill and other places will work just as well. Now, if you do not have ready access to any of those items, you can use a ferrite antenna from an old radio. As a last resort, you can even use a cheap ceramic magnet you can buy at Radio Shack. If you want to know if the material you have will work, first ground balance to the normal ground and then pass the suspected item under the coil. If the signal goes quiet followed by the usual "boing" it should work. Now, some objects do work better than others. Once you have the right combination, simply ground balance to the general ground and then place the nugget next to the rock and pass the coil over the combination. What should happen is the strong negative response from the rock will cause the nugget to be ignored.

Now, I have done this test on most of the VLF's built before about 94 and they all respond the same way. Because of the nature of the design, newer ones should have the same limitations.

Now, before I forget, I am going to jump to a different topic for a second. LST owners cannot turn off the ground balance, but can discriminate out many small pieces of iron such as shoe tacks and small wire by simply using the Alkali mode. This mode is actually the best mode to use all the time when gold hunting, especially since you can't turn off the ground balance. The wider adjustment range will provide a faster and better ground balance which helps reduce the above mentioned problem.

Now, as for discriminating out much of the small metal, all you have to do when you get a target response is to simply make multiple passes over the object. If this signal reduces to nothing or even reduces sufficiently that one can tell the difference, the object is iron. I never had gold reduce at all, regardless of size.

On other detectors having a form of auto ground balance (GB), it is a good idea to test the GB to see if it will try to null weak gold signals. Some designs do that. I know my ML's did as did my Discovery Goldtrax. Personally, I would adjust the ground balance for the conditions as determined above and then lock the GB to that setting in most cases. However, this is something a person should determine works best for them. Just remember, if the unit ground balances to the general ground and you start getting the negative signals, followed by the "boings", it will be much easier to miss gold nuggets.

Now, the bottom line is a VLF is much more demanding when it comes to adjusting for maximum depth. Adjust it improperly and your depth capabilities will drop significantly. The key is to practice, practice, practice. Try different things and see just what happens. Don't take my word for it. Also, don't rely on a test of one. When you look at the signal from gold on a scope and then look at the signal from ferrite, one can see just how easily the rock can overcome the gold signal.

If a nugget is buried deep, then the signal is even smaller. This makes it easier for even a pea size piece of magnetite to easily cause a 1/4 oz nugget buried a few inches below it to be missed. Remove the magnetite pebble and the same nugget would easily be detected. Adjust the detector to ignore the magnetite and again the nugget will respond properly and be heard.

Now, one major advantage of a PI is the simple fact, magnetite does not cause nuggets to be missed. In fact, on the ML, such magnetite rocks will have a tendency to generate a response which can cause people to suspect a nugget signal. If there happens to be a nugget below the magnetite rock, the nugget signal will come through loud and clear. In fact, the magnetite may just enhance the nugget signal.

I did mention something about this condition earlier. It appears that magnetite in rock or black sand form can, under certain conditions, cause a stronger response from a buried nugget on a PI. This can help account as to why we may find nuggets deeper can be demonstrated later.

So, what wreaks havoc on a VLF can actually help a PI. About the only way to use the magnetite like the PI's do is to ground balance such that hotrocks such as magnetite do not cause a negative response, but always cause a very slight positive one. If this is done, then much less gold will be missed. Unfortunately, it will make the threshold noisier also. This will generally require the autotune be sped up or the gain to be turned down some to make it tolerable.

Reg

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Hi Inhere,

Your statement "I have seen many demo’s and yes they may be flawed." reminded me of a promo they used to do with the XT17000, I believe to show how great the auto ground balance was. What they would do was to take a nice size nugget, maybe a 1/3 oz or so and place it under a piece of magnetite. Then they would pass over the rock and nugget combination and note how the nugget was ignored. Then they would pass over the rock again making a few passes and suddenly, the auto ground balance would adjust to the magnetite and the nugget would be heard.

They were careful to place the rock and nugget where the ground would not influence the test, like on a wooden table.

That used to amaze people. When I saw it, I thought to myself, how many people are going to take time to make a bunch of passes over each rock they encounter. One would have to do that since once the coil passed the rock, it would readjust to the ground again and the procedure would have to be repeated.

Now, the test did display how well the GB worked on the XT's. It seemed to work very well. On the down side, I found the GB would also try to null out weak gold signals also.

Anyway, the demo worked quite well to display how a rock can cause a large piece of gold to be ignored and what needed to be done to mnimize the problem. This little demo really needs to be done for new owners so they can see what can happen and how to avoid it and noted as such, rather than simply try to display the ground balance feature.

As simple as the demo was, it clearly displayed how one can easily change the depth of detection by adjusting one feature.

BTW, anyone else remember this sales promo technique?

Reg

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Hi Reg,

I have found your writings a lot more interesting then you may imagine.

I have been looking for a VLF for my wife. She's only small, so I can't get anything too heavy.

The 17000 and 18000 don't impress me much, I hate the cheap plastic boxes they use too.

I would have liked to buy the GB2 because I could have used it myself on a lot of dredge dumps.

At the moment I like the Xterra 70, but whereas you guys can buy them for less then $700.00 with the DD coil thrown in. Over here they want $1150.00 for the detector and another $195.00 for the DD coil.

If I had the time, I would be better off buying it over there and getting it sent here. <_<

I'll have more to say about those tests I mentioned, after Gary posts the Finders test.

I haven't seen the Finders test myself but I know about some funny things that happened around that time.

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Hi Rob,

You said " Reg Sniff should know by now, if I egg him on enough about the PI's he will post very informative information about detectors. :D "

Yep, you know I will take the bait if it looks like a good topic.

Now, you also said

-------------

"However, I have one question .... "If my Minelab PI would find a small nugget at 4 inches deep and a VLF could only hear the same nugget at 2 inches, wouldn't that be 2 times the depth? :huh:

Minelab did make the claims that the PI's were getting 2-3 times the depth over conventional VLF detectors. They also stated the GP Extreme was getting 55% better depth on small nuggets and 18% better depth on larger nuggets over the SD series.

I would agree in mineralized ground that the Minelab PI's are getting twice the depth. "

------------

Now Rob, to use your definition, when I tested the SD 2100 using the 1/4 oz nugget, I could only get a depth of about 3" but that particular nugget was found with a VLF at almost 9". So, by your definition, the VLF will go 3 times deeper than the ML PI. Right?????

It gets better, you know I have a couple of John Blennert's "invisible nuggets" I use for testing. You also know that no ML PI can detect these particular nuggets.

However, you also know my little PI will detect them and they were found with a VLF, so in this case by applying your logic, VLF's and low powered PI"s go 100% deeper than ML PI's. Right?????

(gotcha)

Cheers,

Reg

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Hi Inhere,

In response to your quest for a VLF, I personally liked the XT18000 better than the XT17000 because the sound was much smoother. Now, I liked them both for ease of use.

In fact, I still have one of my XT 18000's I keep around because it is so easy to use. I can show the most inexperienced user how to use it once and they will generally know what to do from that point on. Now, I don't like the weight ratio when the control box is mounted up on the S handle by your hand. I prefer to mount it under the forearm for balance. This setup works great for females because it makes the unit to appear lighter. Now, I also Velcro it in place also because it will fall off quite easily.

The GB 2 is also a great detector. It is a little harder for a novice to use because of the manual ground balance. Now, I really do like the discrimination feature on this unit. I have always cautioned people about using any form of discrimination when gold hunting simply because it is real tough to find a design that works well. However, the GB 2 discrimination mode does work well.

Generally speaking most discriminators really suffer when magnetite rocks are anywhere close. You can compensate for them in the all metal mode, but not easily when using the discrimination mode. There are a couple of tricks that do help though. So, the strong response from Ferrite will cause a nugget to be rejected much like it is in the all metal mode when the ground balance isn't correct. As for the GB 2, this unit is much more forgiving and the magnetite rocks do not influence the discrimination mode nearly as bad on it as they do on other VLF's I have tested.

To be honest, I was only interested in one new VLF and that one was to be the new version of the Teknetics Mark 1. Some time back George Payne indicated he was interested in designing a new updated version of his original design. Unfortunately, the last time I talked to George, he indicated the project may never be completed. That is too bad because the original Mark 1 was years ahead of any of its competitors. Now, what made this new unit really appealing was the fact that George said there was a whole lot of room to improve the depth plus a few other features. Now, I am not much into coin hunting any more, but some of the techniques he was going to use would make this new version a real killer on gold also. It is too bad it may never exist.

Now, I have not used the Xterra so I will refrain from offering an opinion.

I do wish you the best with your decision.

Getting back to using the discrimination feature on detectors such as the Tesoro Lobo, the LST, the GB 2 or one of the other true discrimination units, most will suffer because of the magnetite problem. Now, the trick I used to use was when I came across a signal that was near a rock, I would scan the area a certain way.

In most cases, a nugget will snuggle up against a rock because it is a convenient place to stop. Now, if you scan from dirt to rock or visa versa, you will almost always have problems getting the discrimination mode to work correctly. However, if you scan the rock's perimeter and try to keep the center of the coil right at the edge of the rock, you will have much less problem because of the magnetite in the rock. The trick is to try to keep the rock under half of the coil at all times. By doing so, you reduce the sudden signal "step" the filters in the detector see if your were to go from dirt to rock. This allows for the gold signal to have a much stronger signal ratio. The trick isn't foolproof but it does help.

Reg

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