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  #61  
Old 01-08-2018, 10:10 AM
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Air tests are of value, many of the high audio gain units will air test silly deep, mine gets a silver dime at about 14" with a sniper coil, but in my soil it would be around 50% in ground with said coil.
Mild soil is where the high gain units shine on depth.

Originally Posted by George (MN) View post
Outside, people would only consider a valid test one with no EMI. But indoors, people are divided as to air tests being the highest setting that provides a beep, or is it the highest setting that gets a beep without any extra noises?

The in house noises are not likely heard at the nearest park or school.

Almost any detector will air test 10" on a dime if average or above. Some cheaper units will air test 8"-9" on a dime. Anything that does 11"+ amazing.
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  #62  
Old 01-08-2018, 11:16 AM
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Originally Posted by ohiochris View post
But that dont make him correct , and my earlier point addresses something he is not taking into consideration. With his job , he is an authority on detector design , not necessarily an authority on all things detecting. A job title does not trump the combined experience of many long time detectorists who have seen and experienced in the field the very thing he is trying to dispute. But thats ok , until you actually get the chance to see it for yourself , the doubt is not surprising.
I am willing to bet that an engineer that designs detectors knows a bit more about the physics and chemistry involved, the ground matrix, how detectors react, etc - than do most detectorists do. So, I am far more likely to take the work of a guy who has to design around the problems of mineralization, ground matrix, soil conductivity, etc.

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  #63  
Old 01-08-2018, 11:51 AM
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Mr Dankowski, who's well known in this field also leans towards the electrical grounding of the coin.
"The longer a metallic item is in the ground........... the more compacted the dirt....... in general...... around that object. This allows a much better 'electrical connect' with the ground. The metallic object is more 'grounded'. If the object leaches into the ground........... the 'electrical connect' with the ground is greater. It is not the oxides that provides a better/larger detection of the object............ rather............... it is the fact the metallic item is well grounded...... allowing better detection.

Too much emphasis is placed upon the 'halo'. More focus needs to be placed on the enhanced 'electrical connect'. "
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  #64  
Old 01-08-2018, 12:00 PM
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"Halo effect" or "Electrical Connect" call it what you like but I have personally experienced the phenomenon. It happens! The thing is it is really quite rare. I think some make it sound like it happens on every other coin when in fact it's far more infrequent. Of course the ground and age of the site are major contributors to how frequent, but it is a rare happening. At least for me.

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  #65  
Old 01-08-2018, 12:15 PM
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Originally Posted by Detector View post
"Halo effect" or "Electrical Connect" call it what you like but I have personally experienced the phenomenon. It happens! The thing is it is really quite rare. I think some make it sound like it happens on every other coin when in fact it's far more infrequent. Of course the ground and age of the site are major contributors to how frequent, but it is a rare happening. At least for me.

It may not be as rare as you think. Who knows to what extent it has helped to find things when we never really stopped to think about it or investigate it. I tend to think its a bigger part of our success than we know. Its considered sound logic and has been demonstrated many times how long buried coins can be detected better than fresh buried coins , whether thats because of a halo or because of ground conductivity ( which is essentially the same ) the effect is the same. Its something that usually gets better with time , atleast with most single frequency vlf detectors. If it ever happens at all , then it may be happening atleast in some small part , with every long buried target we have ever found. That dont mean you wouldnt have found it otherwise but that slightly larger profile is still there. It only becomes noticeable in extreme situations.

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  #66  
Old 01-08-2018, 12:34 PM
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Originally Posted by BottleCapKing View post
I am willing to bet that an engineer that designs detectors knows a bit more about the physics and chemistry involved, the ground matrix, how detectors react, etc - than do most detectorists do. So, I am far more likely to take the work of a guy who has to design around the problems of mineralization, ground matrix, soil conductivity, etc.
I agree with that , but it dont rule out the experiences and conclusions of many long time experienced detectorists. There was a time when setting a negative ground balance was considered useless and without basis by engineers and developers , but some have actually come around to understand it as useful in some situations because the experiences of many in the field told a different story. There was a time when the" experts " would not admit that there was a difference between a long buried coin and a freshy , well they are coming around to that too but they are trying their darndest to explain it as something else other than the halo effect. There was even a time when air testing was considered the best way to test a detectors performance , well that theory was blown away a long time ago.

It is what it is , we can all only rely on our own experiences no matter what anybody else says.

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  #67  
Old 01-08-2018, 12:59 PM
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I would tend to agree. Although the designer would know a lot about the "physics" of the workings of a detector, they rely on experienced field testers to determine if their concepts work or not or are good or bad. Kind of like being a car designer doesn't make you a grate driver.

Anyway, I'd put my money behind the choice of the experienced user before the designer. But hey, that's just my 2 cents.

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  #68  
Old 01-09-2018, 02:24 PM
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Originally Posted by Detector View post
"Halo effect" or "Electrical Connect" call it what you like but I have personally experienced the phenomenon. It happens! The thing is it is really quite rare. I think some make it sound like it happens on every other coin when in fact it's far more infrequent. Of course the ground and age of the site are major contributors to how frequent, but it is a rare happening. At least for me.
Yes it does Happen. I have had many a good solid hit disappear when I start digging. Out comes the AT Pointer! lol

FBS machines do a terrible job air testing but if you have a deep coin that has been buried for a few years it will hit it. You cant air test or have freshly buried targets to test a Minelab E-Trac or Minelab CTX 3030. It seems to take at least a year before you have a good idea with them.

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  #69  
Old 01-09-2018, 02:38 PM
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I've also lost my signal on coins after i've turned over the plug, some of the coins were a number of inches below the plug undisturbed, but if it still had an undisturbed halo why would i lose the signal?
I found i lost my signal more often when i disturbed the coin when removing the plug, and the coin went on edge, or too deep a plug and the coin fell back to the bottom of the hole, or the coil didn't like the air gap left after the plug was removed etc etc, just too many variables to say it was because of a halo imho.

Originally Posted by Big Boys Hobbies View post
Yes it does Happen. I have had many a good solid hit disappear when I start digging.
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  #70  
Old 01-09-2018, 02:51 PM
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FBS machines do a terrible job air testing but if you have a deep coin that has been buried for a few years it will hit it. You cant air test or have freshly buried targets to test a Minelab E-Trac or Minelab CTX 3030. It seems to take at least a year before you have a good idea with them.
You know I used to think that the FBS's were the exception simply because, as you said, the air test sure didn't reflect the in-ground results. But, I did get to fiddling with the setting on my E-Trac and was able to get very good air test depth.

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  #71  
Old 01-22-2018, 04:12 AM
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Originally Posted by ghound View post
I've also lost my signal on coins after i've turned over the plug, some of the coins were a number of inches below the plug undisturbed, but if it still had an undisturbed halo why would i lose the signal?
I found i lost my signal more often when i disturbed the coin when removing the plug, and the coin went on edge, or too deep a plug and the coin fell back to the bottom of the hole, or the coil didn't like the air gap left after the plug was removed etc etc, just too many variables to say it was because of a halo imho.
That happens because you changed the variables , the halo is still there but now something about how you changed the immediate area has caused the target to get masked by something else in the soil. The only sensible reason for you to lose your target at that point is masking , and that can happen whether the halo is there or not.

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Old 01-22-2018, 04:33 AM
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Originally Posted by ghound View post
Mr Dankowski, who's well known in this field also leans towards the electrical grounding of the coin.
"The longer a metallic item is in the ground........... the more compacted the dirt....... in general...... around that object. This allows a much better 'electrical connect' with the ground. The metallic object is more 'grounded'. If the object leaches into the ground........... the 'electrical connect' with the ground is greater. It is not the oxides that provides a better/larger detection of the object............ rather............... it is the fact the metallic item is well grounded...... allowing better detection.

Too much emphasis is placed upon the 'halo'. More focus needs to be placed on the enhanced 'electrical connect'. "

The problem with this theory is that better electrical connection to the ground is often why you actually get less depth in the soil than in an air test. Halo or not , you would likely get better depth in Styrofoam ( which is an insulator ) than in the ground in many areas......to me that means electrical connection with the ground not a factor in getting better depth on long buried coins. But let the minerals off that coin leech into the surrounding Styrofoam and see what happens..... that area surrounding the coin which was previously not conductive , is now conductive....an expanded cloak of conductivity surrounding the coin....an island of conductivity in middle of an insulator.

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  #73  
Old 01-22-2018, 09:39 AM
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I'd say NASA Tom has crunched the numbers on this one.
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  #74  
Old 01-22-2018, 02:21 PM
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Originally Posted by ohiochris View post
On more than one occasion , Ive pulled a coin from the ground and still got a good signal from the discolored impression left in the ground by the coin until further inspection destroyed the impression and scattered it , poof ! no more signal. That's the halo , and it can work even when the coin is gone. That equals bigger target profile. With all the experience you guys have , its hard to believe you never noticed this happening yourself.


The controversy continues.....
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  #75  
Old 01-22-2018, 03:43 PM
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Shorty answer, Yes! Long answer, not as often as you'd wish.

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  #76  
Old 01-22-2018, 04:13 PM
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The eddy current is what penetrates the target,then reports Back to the coil.How much it penetrates the target before reporting back is how the conductive scale is processed by the brains of your machine.The eddy current cannot penetrate a (halo) ,,it only penetrates solid masses of metal..Sorry, But I cannot agree with a halo affect for that reason,although I can see how metals could bleed out over time in the ground,the eddy signal couldn’t possibly penetrate bleeding.

Last edited by woodbutcher; 01-22-2018 at 07:42 PM.
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  #77  
Old 01-23-2018, 10:49 AM
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Originally Posted by woodbutcher View post
The eddy current is what penetrates the target,then reports Back to the coil.How much it penetrates the target before reporting back is how the conductive scale is processed by the brains of your machine.The eddy current cannot penetrate a (halo) ,,it only penetrates solid masses of metal..Sorry, But I cannot agree with a halo affect for that reason,although I can see how metals could bleed out over time in the ground,the eddy signal couldn’t possibly penetrate bleeding.

Ummmm ,....problem mineralized soil and hot rocks as well as rust pockets where a solid item " used to be " all disprove what you just said here and anything conductive enough can be induced to produce an electromagnetic field , it is that field that is processed by the detector.

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Old 01-23-2018, 11:00 AM
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Originally Posted by ohiochris View post
Ummmm ,....problem mineralized soil and hot rocks as well as rust pockets where a solid item " used to be " all disprove what you just said here and anything conductive enough can be induced to produce an electromagnetic field , it is that field that is processed by the detector.
That's not my theory,just what I've read from different scientist who study not only metal detectors,but all ground penetrating systems.Hey,you could be right,and they could be wrong,I'm just repeating what the experts say.Google ( what is Eddy current) and see for yourself

Hot rocks are a solid mass,not sure about hot dirt tho,never heard of it.
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Old 01-23-2018, 11:07 AM
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I didnt write this but its a good read......... http://www.njminerals.org/metaldetec...aloeffect.html

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Old 01-23-2018, 11:24 AM
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Originally Posted by woodbutcher View post
That's not my theory,just what I've read from different scientist who study not only metal detectors,but all ground penetrating systems.Hey,you could be right,and they could be wrong,I'm just repeating what the experts say.Google ( what is Eddy current) and see for yourself

Hot rocks are a solid mass,not sure about hot dirt tho,never heard of it.

Hot rocks are not a refined metal , many are not even completely solid but a mass of various mineral bits sticking together in a clump.....of course there is no " one " type of hot rock they could be anything , but many are not as solid as you think. I have read up on eddy currents , the role they play really dont have an effect on whether a halo can be detected or not since in some cases the halo can be read by the detector as a solid metal target in its own right. Metal detectors are in reality " mineral " detectors.....just tuned to be more effective on certain minerals or concentrations of minerals over others.

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