GPZ Low-high Signals And High Yield Vs General

[Norvic]

True, recall back a in 14, I`d got a reverse booming signal in a shallow ck, bedrock showing in places, just on dark, I`d just spent a few hours on digging up plenty of ferrous but no gold, so I left that signal. That night thinking about it, went back first thing in morning straight to signal and it was a 27gram solid 6" down in clay, so that got me out of pessimistic mood and got up on the ridge scoring a nice tight patch. Never learn, I`ve done that over the years too often should have known better.

 

Imagine we all have such experiences, and no doubt I`ll do it again and again. Very difficult to stay positive all the time I guess, positiveness is probably more important than persistence. Probably should pack up, tune into some good C&W, a beer, feed and have a spell at such times. Defragment the grey matter.

[jasong]

I guess I'm missing something, it sounds to me like Lunk is saying exactly what I have been saying, and that is that he found another large nugget that went high-low in Normal. We've already established they tend to reverse in Difficult.

The oddity is that everyone the US seems to be getting normal signals on everything above 1/4 oz or so, yet all the Aussies in this thread are reporting the opposite.

Maybe it means nothing, true. But I've just gone back and retested all 13 of the nuggets I've found this trip over 1/4 oz and every one of them goes high-low, even if I balance the detector to a big chunk of magnetite or to sand, I can't force them to reverse. 7 to 39 grams, 13 nuggets. Bit more than a statistical oddity.

Anyways, who knows. I found it interesting and worth paying attention to myself. What I do know is that the GPZ definitely is sensitive to different geometries and physical distributions of gold just from the types of nuggets it screams on and the GPX is silent on alone.

*Also, the warbly response occurs regardless of ground balance too so the tones must be in at least some way related to the actual target itself.

[Steve Herschbach]

It is an accidental artifact of the ground balance system in combination with the other settings and where the gold in question falls in relation to those settings. The ground balance only has a certain amount of range and will only tip a small number of nuggets back and forth as they must be right in the zone where that tipping occurs. Most nuggets will read one way or the other, and that is that. The reference I posted above about TDI relic settings is enlightening regarding this. Reg posted a great chart that tries to graphically show this for the TDI at Link deleted since Findmall Forum update broke all old links The TDI uses a simplistic subtractive methodology for ground balancing plus has a manual ground balance and so makes an easy case study. Minelab units are employing more sophisticated methods so the resulting tones are more complicated but allowing for that mirror what I have experienced with the TDI, Infinium, and ATX plus SD, GP, and GPX detectors.

The fun part is no matter what you do, any particular ground rejection method causes gold that reads just like that ground or hot rock to be lost (or masked). The GPZ is succeeding to some extent simply by being different and therefore exposing gold masked with other ground balance methods. You ever wonder why certain hot rocks can't be tuned out? They can be, but to do so would also eliminate an unacceptably wide range of possible nugget sizes.

[robby_h]

Simple pulse induction ground balance is achieved by subtracting a late amplified ground sample from an early sample, ie, if the second sample is adjusted to equal the first sample then we have GB, but for most small bread & butter gold the nugget's signal in the early sample will be much higher than it's signal in the late sample so the audio goes high in tone. As the nugget size increases, we eventually get to the point where the nugget's signal in the late sample is greater than in the early sample and the audio then goes low.
Size isn't the only determining factor though. In one case a solid smooth 12 grammer might give a low signal but a larger lump might give a high signal if it is made up of smaller bits all joined together or smaller bits joined to a larger mass or if it's a specimen. This is because the small bits increase the amplitude of the early signal relative to the late signal. It should be obvious by this that purity doesn't necessarily determine the tone.

The ZED isn't a conventional PI and has to deal with an additional ground signal but the outcome is much the same.

This is the basis for the TDI's time constant discrimination but it only works when used to ID solid man made objects such as coins and rings, mainly because irregular shaped nuggets and specimens can easily give the same signal as iron junk. If anyone is interested, Bruce Candy explains it well in a 1996 patent.
 

[Steve Herschbach]

Ah Robby, you are the man!

Now, as I understand it with the SD 2100 we have two ground balance "channels". Flip a switch and ground balance channel one. Then flip a switch and ground balance channel two. Then switch to both.

With the TDI we have one channel, and a nugget that falls exactly where the ground balance is set is tuned out also.

With the SD there is the second channel that is offset so the ground balance point is in a different location than in the other channel. The detector looks at both channels, and reports the channel that has the best target response. A nugget missed in channel one gets reported by channel two, or vice versa. Thus Multi Period Sensing (MPS). Later Minelabs hide all this and make it more automatic but it is still there on all MPS based models.

The ground balance point and therefore the tones should shift slightly depending on the channel doing the reporting. You can purposefully run in one channel or the other and can purposefully misadjust the ground balance setting. With the TDI you can create three classes of targets. Those that are always low tone, those that are always high tone, and those that flip back and forth depending where you set the ground balance. It does form the basis of a discrimination system no matter how crude. I always thought it would be neat to have a detector test somehow via MPS make that comparison automatically and report the three target classes via three tones instead of two.

I have sort of wanted to get a SD2100 to play around with this kind of stuff but at the end of the day it takes time I can use to just go find gold.

[Norvic]

This ties in with what I have experienced, especially the smooth solids over the more broken pieces, a recent 58 gram solid gave the reverse signal all the way through the dig even when exposed. (Z was in auto GB throughout) That particular piece is just a slightly oblong "marble", only slightly higher than its width and length. Wish I`d kept the 2100, got bugger all for it year or so back, would be interesting to adjust the GB channels to alter the signal.

 

Maybe of interest, I braved our heat and went out for a couple of days last week, one reverse quiet signal dug down about a foot through the slate, thought had to be gold but was a 1.5" square old time nail. Naturally it gave the reverse signal all through dig and on surface. I have never understood why some prospectors consider they can tell by the tones, never have been able to, just thought it was my feeble hearing.

[jasong]

Then we have another Aussie nugget going reverse and another US nugget going high-low... Just an odd pattern. I'm still curious if anyone in the US has a 1/4 oz + nugget that went reverse the whole dig in Normal?

I agree with what you guys are saying regarding PI ground balance, I'm not so quick to apply SD/GP/GPX ground balancing characteristics to the GPZ myself though. Unless someone has some info about the GPZ that I haven't read yet?

What I do know is that the GPZ uses an entirely new coil to accommodate it's different ground balancing algorithm - the DOD. It also looks at an additional ground component which the GPX did not. We also have the ferrite and the spaghetti dance. So the GB procedure is also different too, not just the balancing algorithm.

Anyways, just to be clear here, I did not suggest to use tones to discriminate - so there is a kind of tangent discussion occuring simultaneously to my original subject. I suggested there is an odd pattern with the tones, which may potentially indicate, among other things, that the GPZ may have some discrim ability that we could possibly see in a future update. I'm not suggesting to anyone to go out and discrim iron with it right now or to do so with their old GPX's. My main intention is to investigate the tone pattern peculiarity.

I'm not sure if I'm misunderstanding and people are telling me there is no such peculiarity, or if the topic of the thread has changed and people were not replying to me but talking about something different to each other and I was interpreting their responses to be directed at me?

[Norvic]

Jasong, Last thing I`m trying to say is there is no peculiarity, there certainly is, I don`t believe it is a variation because of some difference in ground conditions. I`m am simply reporting my experiences. The thread has probably expanded a bit from where you started but that is, I feel because it is very topical. I think Lunk may have hit on something I`m going to test. I run in difficult most of the time and the next reverse signal I`ll switch back to normal, before dig. This is a very interesting thread and with the subsequent  posts  there appears to be a technical explanation to our experiences.

[jasong]

Oh ok, I thought you were running in Normal. Yeah, probably half or more of my 1/4 oz+ nuggets reverse in Difficult too.

I can't even force one to reverse in Normal though. So when I read reports about other people with different machines saying most theirs reverse in Normal, something is odd and worth investigating further IMO.

I'm assuming we all have equally functioning machines so the difference is either in the nugget, the ground, or the machine algorithms iteself. And I can eliminate the ground in experiments easily enough by keeping it constant and testing different nuggets in the exact same spot with the same settings.

[Steve Herschbach]

You asked about the tones Jason so I told you what I think they are about. I personally think the GPZ can be made to discriminate but that the tone observations have nothing to do with that possibility. For the record, I am the one that is suggesting that knowledge of the tones can be applied to discriminate targets but in a manner totally different than what I eventually expect from the GPZ. For me it is two separate subjects.