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Goldscan Depth Question

S

steve herschbach

New member
Hi,

I've read a few posts that indicate that the Goldscan 5 can get more depth in the regular PI mode as opposed to the ground balance mode. I assume this is in a low mineral situation, as it would make no sense to use ground balancing if it resulted in less depth in mineralized ground.

So first question is... is this true? And if so, why? If you are in clean quartz sand with zero mineralization, what amount of depth loss can be expected going from regular PI mode to ground balance mode? At what point can it be expected that the ground balance mode would offer superior depth? Is it pretty much just a "bury target and compare" situation?

Does the ground balance circuit aid at all in a salt situation, like you might get in Florida, where there is no iron mineralization, just wet white sand?

One thing I like about the Goldscan is the ability to switch the ground balance mode on or off, and so I'm trying to better understand the benefits. I am assuming it is different than running an SD Minelab in a single channel, like channel one, as each Minelab channel does still ground balance. The reason Minelab runs two channels is to get gold in one channel the other would miss. Does the Goldscan handle this issue somehow, or is there a "hole" in range of targets that can be detected with the Goldscan?

Thanks in advance for any help with all the questions!

Steve Herschbach
 
Hi Steve
I can't speak for other GS5 users and I certainly can't answer all your questions. I imagine what I am doing is different from most- I don't know really as communication is lacking.

My 2 cents
Yes you are correct. You have a loss of depth when you switch from PI mode to discriminate mode. Actually the more you increase the ground balance clockwise the less sensitive the GS5. The depth loss will be several inches for a nickel.

However, why am I using the GS5? Iron ID is the priority which is different from GP users. My ground is not highly mineralized so I run it in PI mode with a DD coil (monos work too). As you know I run a mag at the same time as my GS5. A non hit with the mag and I stop and check the target in the ground mode. I use the ground balance mode as a metal ID function. The GS5 is actually better at iron ID than the mag but it is faster with my setup.

Got to go- my relief is here
Hope this helps
 
Any time you swirch in elctronic filtering you are going to have more noise and reduced sensitivity with processing than straight signal without modification. You don't lose alot with ground balance, but there will be a difference. Don
 
I have a Gs5b and have reported about it on my forum. In GC mode it loses up to 30% of its depth compared to straight Pi mode. In some places in the USA you would be able to run it in straight Pi mode with a DD coil providing you increase the sample delay. Why does it lose so much depth in GC mode? Well in my view it is a fundamental flaw in the GC mode that nulls out or reduces the sensitivity to targets that have time constants near or similar to ground Tc's and a incorrect Tc's for the integrators.
I may be off the mark but this is my opinion.All Gc circuits cause a depth loss but this should not be more than say 5% as you will see if you test a Ml machine. Check my forum soon as I will have some big news on the Goldscan etc.
Doug
 
Hi Doug,

"say 5% as you will see if you test a Ml machine".

Test a Minelab how?

A 30% depth loss is huge. It begs again the question of how bad the mineralization would have to be before engaging the ground canceling ends up being an advantage rather than a penalty.

Obviously targets that respond close to the ground signal would see a reduction of depth or outright loss. Again, this is why Minelab uses two channels. But for targets that differ markedly from the ground signal there should be no great loss.

Steve Herschbach
 
Hi George,

We have similar interests in that regard. I think I was one of the first people to order a Goldscan, but then backed out as I had too many toys on order. But I'm still interested in the unit. I sold my Infinium awhile back and so am looking at the various "not Minelab" units out there. Looks like this will be the year of the PI unit what with all the rumors flying. Thanks for your reply.

Steve Herschbach
 
Doug I think the ground not as bad in general in USA as OZ, would not have that much reduction, but would suspect about half that amount. Don
 
You can test a ML in tracking mode by moving a target above a coil resting on the ground after Gb'ing. Then repeat in fixed mode. You can also test as we do at the test site at Dunolly in fixed and tracking. You can also do air tests using "standard" targets like coins of different conductivities. If you do this with my GS5b you lose up to 30% in "depth" when in GB compared to straight Pi mode. It is somewhat dependent on the position of the GB and the sample delay and Tx pulse length.But it also worth noting that the ML uses an approx exponential coil current which rises continuously until Pulse termination (which is why you need low impedance coils). The Gs5b uses a totally different approach,as i understand it the coil current in the Gs5B rises quickly to a maximum value and is held there until pulse termination and of course does not use multiple pulse lengths as a ML. All these things effect depth and sensitivity and losses on using the Gb circuit. The Gs5b in my view needs a complete rework of the GB and integrating circuits. If this was done then it would not lose as much depth in Gb mode,give a quicker sharper signal and come much closer to a ML in depth and sensitivity.
Doug
 
On my Gs5b I lose 20% of "depth" just in air tests when I compare sraight Pi mode with Gb mode on a variety of conductive targets, including nuggets.
Doug
 
If yours has a lose of that, you have problems with your unit.

Have it taken care of. Give it to your dealer, and have him check it over. There is most certainly a problem with your unit if that's happening.

Heads up nugget for nugget, size for size, they are some changes, and loss's that happen. On the smallest of targets they are some changes,but that's on a per target bases.
 
Mine is not a std gs5b as it has 2x the receive gain of std units. But what I have observed has been found by others with Gs5B's. Compared to a ML machine with a mono coil of the same size the Gs5b in Gb mode and at 10-12u secs sample delay and 100 usecs Tx is 25%-30% behind my Gp 3000 for depth on nuggets from 1gram to 19 ozs. And there is no authorized dealer here in Australia and I am not going to pay to have the Gs5b sent to the USA or back to Eric Foster to be checked over or serviced.
Doug
 
Doug,

I have been using the GS5 longer than most everyone besides Eric. I am/was a Minelab dealer. I had all their units to compare with, and what your posting just doesn't fit into the picture from what I know. Having that much of a loss, accepting that it isn't caused by the operator, then I stand by my pre. statement, you have something wrong with your unit.

You have a dealer near you, John M. could handle it for you.

If that's not an acceptable way to do it, you also could mail it to Eric using the mail system for a not so strong price. Just send the control box less the battery, and the coil. It will not be a heavy package, and the cost shouldn't be bad ???
 
Hi Steve,

Yes, the Goldscan 5 was designed so that the GB circuit could be switched out, for low and non-mineralised situations. This enables it to double as an effective beach machine, where rings and coins sink to considerable depths in sand. You do get a
 
Eric we need to speak on the telephone,I have a few things that you need to know. JM will give you my telephone number.If not e- mail me and I will give it to you.
Doug
 
Eric my GS5B cannot detect a 1oz nugget at 12" at the Dunolly test site with ANY coil at any sample delay or TX pulse length,nor can it detect any of out larger "standard" nuggets at 18" or 24". My 3000 will detect all of these nuggets with my 18" DD coil and a lot deeper with an 18" mono coil in GB (tracking mode). For me there is no point in using my Gs5B for serious gold prospecting because it is so far behind a ML for both depth and sensitivity. And at the higher gain settings on my machine it does suffer from em noise and ground noise over very high mineralization. I don't mind some ground noise or having to GB several times per hour if I get the depth, but on my GS5b I do not get the depth of my 3000.The tonal ID also is not reliable in my opinion on native nuggets as they can give both wee and whoo signals depending on shape,composition and depth and some iron targets also give both responses from my experience.
Doug
 
Hi Eric,

Thank you very much for your explanations - they are very helpful.

I understand the Goldscan is not intended to compete with the Minelabs per se. But it does because it fills "a demand for a unit that was largely immune to electromagnetic interference, ignored most hotrocks, could be worked in the strongest and noisiest of ground conditions using a mono coil, and was fully weatherproof, and that the supplied coil could be submerged for beach work at the waterline".

I am an avid Minelab owner, but I am one of those people who want the features you described. I most firmly believe no one machine can do it all. I believe there are circumstances where the Goldscan can find gold nuggets that a Minelab might have difficulty finding. I would not sell my Minelab and replace it with a Goldscan, but I sure think a Goldscan would make a great second unit. At the least, it would provide for backup should the Minelab box fail, as all the coils are compatible.

As you may recall, I am one of the few people who really appreciated the Garrett Infinium for many of these very reasons. But that machine has very limited adjustability and a more limited coil selection than the Goldscan 5. And from what I gather so far the Goldscan is far better at handling electrical interference. The main reason I finally sold the Infinium was that although it worked well, it is a very noisy unit in areas of electrical interference and some saltwater environs. It is however totally submersible, which has its obvious advantages.

I am most wanting to have the ability to adjust the pulse delay and have a manual ground balance I can turn on or off. I deal with many nuggets that exceed an ounce in weight, and so I may be able to use more delay than most people and get the quiet operation I want by ignoring rocks that my Minelab hits. Truly, it is the fact that this unit has totally different operating characteristics than a Minelab that excites me. I believe in having detectors with widely differing characteristics, as any one can prove to have a huge advantage under given circumstances. If a Goldscan were too much like a Minelab, I'd not be interested.

In my case in Alaska I have a mine with very pesky hotrocks that the Minelab units do pick up, and some areas with extreme trash. I also have to deal with days of pouring rain and thick brush. Having a unit that can be hipmounted and is water resistant is a real boon under those circumstances. And I would not be afraid to use it near salt water!

Steve Herschbach
Moore Creek Mining LLC
 
Hi Doug,

You are confusing ground balancing versus straight PI mode with tracking versus fixed.

As far as I know, a Minelab always ground balances. There is no straight PI mode. I also know about auto ground balance versus fixed ground balance on a Minelab and the benefits of each setting.

With the Goldscan you are actually turning the ground balancing off. Not the same thing as a fixed ground balance setting on a Minelab. So you are comparing apples to oranges.

Steve Herschbach
 
I do not know of any mfger here that pays postage round trip. If you find gold what's the deal LOL, it would seem better to have it checked before saying the unit doesn't work good in my opinion. Don
 
Eric on a VLF unit gold rings air test about one third of their maximum distance when presented perpendicular to the coil in an air test. I have dug gold bands in one scoop that sounded way deep while wading so I assume that this depth loss applies to in ground rings as well. In your opinion would a PI have any depth advantage over a VLF on this type target?

Also, would there be any advantage depthwise ovler a VLF hunting in fresh water in low mineral quartz sand as Steve asked? Some of the higher gain VLF's are noisy over the ripples in the sand bottom in these conditions even the "silent search machines".

Thanks
Tom
 
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