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  • Steve Herschbach changed the title to Fisher Impulse And The " No Holes " Claim

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I have seen it said a few times now that the new Fisher Impulse AQ has "no holes". This started as a very specific mention on the part of the designer, and now has been expanded into a range of assump

The traditional subtraction GB design subtracts the outputs of 2 channels to eliminate ground. That is, ground cannot be heard, ideally at all. That also creates a hard notch in the target conductivit

So if I adjust a TDI so the ground balance is mid-range, we have a hole. But if I adjust it to either extreme, I’m just rejecting the top end or the low end. It no longer a hole, but a cut off!  S

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First time I've understood the 'holes'  Thanks Steve.  It went some way into explaining the bias and null on the QED too.  Great article.

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The traditional subtraction GB design subtracts the outputs of 2 channels to eliminate ground. That is, ground cannot be heard, ideally at all. That also creates a hard notch in the target conductivity range, whereby there is a hard notch where a particular target (or small range of targets) cannot be heard. Traditionally, targets on the low side of the GB point produce a high tone, and on the high side they produce a low tone. But right at the GB point particular targets produce no response at all.

Hole.jpg.28bea57ec7fca35f750b32e7b2c10508.jpg

In the AQ the GB subtraction is modified to no longer produce a hard notch. Therefore it can no longer provide a true GB function, but it also doesn't hard-notch targets, either.

NoHole.jpg.180a2dab7854c08ba23b9253d5d89291.jpg

In Tone mode as target conductivity approaches the transition point from the low side, targets respond with a high tone, then progressively you start hearing some low tone mixed in. Right at the transition a target produces equal amounts of high-low tone. Higher conductors eventually produce a low tone. But nowhere should any conductivity produce a hard notch in the audio response. That is what "no target hole" means.

Now, you can switch to Mute mode and any low tone responses are eliminated. This means that, around the transition point, targets produce a broken high tone audio. Targets above the transition produce no audio at all, and you can certainly call this a massive target hole but that's not within the spirit and normal definition of what is meant by a target hole. In Tone mode, the AQ lets you hear all targets and you can decide whether or not to dig them. With a target-hole detector, particular targets are simply not detected.

On the salt issue, there is no salt rejection mode other than pulse delay. At 7us you can definitely hear salt but even then I found it reasonably manageable, at least in wet salt sand. In active surf I think I had to back off to 8us, and in deeper water it may need to be higher still. There are limitations to what the AQ can detect at the very lowest conductivities, but that again is not in the spirit and normal definition of what is meant by a target hole. Much like it cannot detect a ring at 3 feet; that's not a target hole, it's a fundamental limitation.

 

 

 

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Hello,

Regarding a metal detector model for finding gold nuggets, I would not comment today.

Regarding the IMPULSE AQ, there is no problem in the conductivity scale of the low conductors.

Let us take an example, on the conductivity scale of a White XLT Spectrum, the non-ferrous going from 0 to +94 and the ferrous 0 to -95.
The AQ pulse detects all targets with a VDI ranging from 0 to 58 as being valid targets.
And the IMPULSE AQ will minimize the loss of depth on the highest VDIs. (almost 55)

VIDEO HERE (Sorry for the rude English)

JW.jpg

2.thumb.jpg.0c5ce483796eea85aef3dc5ee1f6d6d5.jpg

 

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50 minutes ago, Geotech said:

On the salt issue, there is no salt rejection mode other than pulse delay. At 7us you can definitely hear salt but even then I found it reasonably manageable, at least in wet salt sand. In active surf I think I had to back off to 8us, and in deeper water it may need to be higher still. There are limitations to what the AQ can detect at the very lowest conductivities, but that again is not in the spirit and normal definition of what is meant by a target hole. Much like it cannot detect a ring at 3 feet; that's not a target hole, it's a fundamental limitation.

Perhaps I misunderstood. When I inquired previously of Alexandre about being able to get full use of the 7 Us in all metal mode, he explained that the AQ was specifically designed to reject small foil items, and that thin gold chains, ear rings, and other micro jewelry targets would also be lost due to this intention to reject short time constant/low conductive targets. The Gold model were said to eliminate this low end limitation. Again ,perhaps something lost in translation. If all metal mode is a pure PI mode nobody will be happier than I.

Not to sure about the spirit stuff. :smile: I fully admit there are different ways at looking at the subject, and none are "wrong" per se. Or maybe I am flat out wrong... I can live with that if good info comes of it. It is semantics on one side, and what the machine does or does not do on the other. No matter what.... I'm all ears for sure on the great responses. Nothing like a challenge to bring good info to light! 😉

When it settles out and when/if I am proven in gross error, I will edit my post to suit.

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I'm the one who approved the "no target hole" claim, based on my understanding of what "target hole" means. It has been discussed extensively with the TDI to mean any target conductivities that fall into the GB notch and are therefore not detected. I assumed that the same definition has applied to Minelab models, though admittedly I have not been engaged in many Minelab discussions. If I'm mistaken, then we can certainly change the claim to better match accepted terminology. Like you, I'm really opposed to introducing bogus redefinitions of widely-accepted terms just for marketing purposes.

 

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Well I fully admit to shaking the tree here to see what falls out. I’m not aware of Minelab explicitly addressing the issue anywhere beyond the original SD2000 explanation provided by Candy in an old magazine article I have on hand. They’ve always kind of implied and let people assume there are no holes, when in fact every machine they make has some. I’m not aware of any official definition of holes anywhere, just loose talk tossed around mostly among people like Reg Sniff or Eric Foster or you or me or whoever. But nothing really in-depth definitive anywhere I have seen. Any really always mostly around the idea of a ground balance point taking good targets with it. Back to my assertion... the ground balance here is relabeled a disc control, and moved to a certain location to take explicit advantage of the “hole”. Was the goal to eliminate most U.S. coins also, or was that an unintended side effect? If I was marketing I would say a guy like Steve does not want to waste time digging coins at the beach, he wants to dig gold. That is 100% accurate. So for me it is a benefit and could have been designed that way for me by intent.

Or it is an unintended and unavoidable side effect of eliminating the ferrous? Ok, that’s life. But there really are many beach hunters who like the coins. Lots of complaints now about coins drying up due to closures. This inability to find coins while discriminating ferrous would be a big deal to them.

I’m not trying to make a legal case and certainly not trying to step on toes. My main goal is.... what does the detector detect, what does it discriminate, and what gets lost as a result?

I’m really interested in what others think here. It’s not a fight... let’s figure out what a hole is, what it is not. Is a no holes claim valid... what do you all think? Am I being a picky jerk? Do I owe Carl an apology... I’m all in and will be more than happy. But let’s talk about it some more. Great subject.

I will say again... I like the chosen AQ target range and focus, and am very happy to pass on coins! I’m just being pedantic and argumentative this morning. :smile:

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I repeat :
Let us take an example, on the conductivity scale of a White's Spectrum XLT, the non-ferrous going from 0 to +94 and the ferrous 0 to -95.
The IMPULSE AQ detects all targets with a VDI ranging from 0 to 58 as being valid targets.
And the IMPULSE AQ will minimize the loss of depth on the highest VDIs. (almost 55)

It will therefore detect between 59 and  94 the targets as invalid

If your coin is at 75 it will not detect it.

An 18K gold signet ring of 20grs is only 45 therefore detected !

Can be that a signet ring of 45 grs 18k will have a VDI of 70 (I don't know I have never seen one) then it will not be detected in MUTE mode and it will make a low tone in TONE mode. (But there will not be the double beep which shows more than 95% the presence of a ferrous)

 

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I thought that holes in detection were only evident in single channel pi detectors and when they went to multi channel pi detectors that hole was closed up mostly???

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5 minutes ago, Mxt Sniper said:

I thought that holes in detection were only evident in single channel pi detectors and when they went to multi channel pi detectors that hole was closed up mostly???

Mostly is the key word.  Name one timing on the GPX that misses no nuggets that can be found with some other timing. How does the GPZ find gold the GPX misses? There is also some gold the GPX does better on then the GPZ.

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