Iron masking/Silent Masking. Credit: Thomas Dankowski

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Oxgirl
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Easylife wrote: Mon Dec 06, 2021 10:20 pm Watch out, it looks like Bruce has his divining rods out! :o :lol: :thumbsup:
He does have some :D
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Oxgirl
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Blackadder43 wrote: Mon Dec 06, 2021 10:11 pm Thats assuming an iron object 'close by'

Dankowski experiment was 'directly over'
Reactivity wont make any difference in dankowski scenario

also as the machine sees the staple irrispective of whether its discrimed out, notched or any other form of hiding iron, and the iron whatever it might be is directly over the good find
The machine still see's it, usually first and its presence affects the signal going down and the same signal returning to your machine
Therein lays the issue he is pointing out

Technology has not made a solution for this scenario as yet :thumbdown:
And I doubt it will. It’s similar to items on a table in front of us. If one is above the other and the top one is bigger we won’t see the smaller hidden one.

I know cause it happens to me regularly with stuff thrown on top of my phone or car keys :lol:
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DaveP
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Oxgirl wrote: Mon Dec 06, 2021 10:48 pm And I doubt it will. It’s similar to items on a table in front of us. If one is above the other and the top one is bigger we won’t see the smaller hidden one.

I know cause it happens to me regularly with stuff thrown on top of my phone or car keys :lol:
It's the other way around. Dankowski is showing a smaller item on top of a bigger one will stop you seeing the bigger one. And, even if you can't see the smaller one it still hides the bigger one.
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Charles Abbeyville
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I would really like Gary to do a vid on this eh? :thumbsup:
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Oxgirl
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DaveP wrote: Tue Dec 07, 2021 11:44 am It's the other way around. Dankowski is showing a smaller item on top of a bigger one will stop you seeing the bigger one. And, even if you can't see the smaller one it still hides the bigger one.
I was making a joke ;)
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keyfits
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When you are after a permission and the Farmer states "it's been done loads of times" as an excuse not to give you a yes, you can show them this article and all will be fine because we have proof now that a field is never done.
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TheFenTiger
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Having just done a very unscientific quick air test I am calling this out. I took an Edward groat, put a standard paper staple on top of it and both the Deus and Nox gave massive clear signals. In fact, neither could see the staple at all on its own. Now it may be because the groat has a larger mass than the staple but the report infers this shouldn't matter. Now I didn't have time to put the staple higher than the groat but it will be interesting to see if this makes a difference. I was also going to try to put a screw on top but again I had to get back to work.
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Blackadder43
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Just for a bit of background info on Thomas Dankowski
He is obsessional with his experiements and the logging of data

His test garden is perfect in its construction and is old and settled too

Plus he is not just a detectorist, he did actually work for Fisher in the research and development of many Fisher machines, the most famous one which commands good money still is the CZ-3D machine
If the serial number matches the database of machines caliberated by Dankowski then they can command twice if not more their value when selling
Plus he also worked for Nasa too

Sorry to be a geek :ugeek: , but air tests prove nothing really and this test was done in situ on his test garden
But it was also 20 years ago now and technology has moved on a little bit

I suppose its impossible to replicate his experiment in its true form, but i posted it to remind people that some of our finds are masked by iron in the ground and we are actually missing stuff with current technology we have

You often see posts made by people who say "very iffy signal and i very nearly didnt dig it", but end up with a decent find and iron present in the same hole

I suppose it comes down to how many times we have a signal that has a piece of iron directly above it in situ
Most times the iron will be off set from the target and thats where your machines reactivity and recovery comes into play

As i said though for a hobbyist detectorist then its a good read, but can be largely ignored
Its only with obsessional geeks like myself who try to swing all the odds into my favour when detecting
I still find mostly rubbish, but i do try :lol:
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Charles Abbeyville
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I'm no boffin but I'm pretty sure the staple would have to be inches ABOVE your groat, not on it. The signal must hit the staple first and then scatter/disperse the signal before it reaches the groat or whatever target and then as the disturbed signal bounces back it has to go through that staple 'sound barrier' once more so by the time you hear the response it's 'garbled'.
That's how I interpreted the info, not tried it though.
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DaveP
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Got some new earbuds yesterday so thought, why not try the buds and the iron masking at the same time!

I'll review the buds once I've given them a good field test but I checked everything with the buds and just with the Nox speaker.

First checked I could detect a single staple - did that with an air test. Difficult but it did register about an inch from the coil but it wasn't consistent.
I've got a bunch of silver sixpences on the desk so just chose one of them - 1920 which has a decent silver content. Quick air test showed a solid 2 way signal at ~9". So far so good.

Into the garden to find a quiet spot. Doh! Loads of digable targets, loads of iron signals - kids eh! I eventually found a reasonably quiet area but there was still some iron background. I even did a factory reset and used the standard programmes to make sure I hadn't mucked up anything with twiddling.

Dig a hole aprox 8" deep, sixpence in, clod on - nada - not a squeak.
Take the clod out so effectively an air test - nada.
Take the sixpence out, repeat air test - easily 9"
Back in the hole (no clod) - increase recovery speed - nada.
Add a small amount of earth - iffy signal with iron tones - might be dug on a bad and desperate day!
Take sixpence out, add some earth to reduce depth, coin in - iffy signal.
Add the whole clod - nada.
Clod out, check the clod for signals, some iron but not focussed.
I tried everything on MF and single frequencies and all pre-set programmes including beach!
Tried with and without GB
Didn't bother with adding the staple to the test.

So what did I learn - I need more alcohol :thumbsup:
1. The air test out of the hole and in the hole are not the same - forget air tests!
2. Adding the clod hid the coin - possibly due to iron
3. Sometime in the future somebody else will find a sixpence as I couldn't be bothered to dig it up again.
4. I really haven't a clue what's going on :lol:
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Easylife
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I just tried this in the house in air so not ideal conditions but good enough to draw a conclusion. I used a 1" rusty nail directly above a button then a silver sixpence and a florin. When the non-ferrous item is about 2" or so from the iron it then becomes completely masked and cannot be heard. The closer the iron is to the coil the greater the masking is by far.
Conclusion: I wish that I didn't know about this! :cry: :cry: :cry: :lol:

Note to self: Dig anything with the slightest squeak! :pulling hair out:
D2 - 13"x11" coil - audio only.
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Easylife
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Easylife wrote: Wed Dec 08, 2021 7:46 pm
Note to self: Dig anything with the slightest squeak! :pulling hair out:
I actually often do if I'm in the mood, an iron tone with just a very broken higher tone, and the target is not very often iron. I guess that's the SMF difference though? :thumbsup:
D2 - 13"x11" coil - audio only.
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