concentric vs DD strange findings

[dfmike]

I made further air tests with the stock concentric coil vs the 11 DD coil on all my detectors (Omega 8000, F5 and F44) and this time I was only looking for target ID's and sound just to see if both coils would react the same. I already knew that ID would be slightly different for both coils and from machine to machine because categorization is different BUT I was surprised that the DD coil/detector combo (on all mentioned detectors) had issues with recent Canadian coin ident. By recent I mean year 1990 and up. All detectors have no problems identifying recent coinage (dime, quarter, nickel, loonie, toonie) with their stock concentric coils and 9" elliptical for the F44. Put on the DD coil on each of them and it becomes interesting. No problems on copper, silver and a recent USA dime which is the only recent USA coinage that I had on hand but the detectors suddenly had serious issues identifying the recent CAD coins mentioned earlier. I set the detectors on 2 tone mode, discrimination at 14 and both would identify these coins as iron with accompanying iron grunt. Sometimes the grunt would only sound on one pass. The F5 with these settings could barely "see" the recent loonie at all. The dime was completely invisible. On the F44 I notched out iron initially and it couldn't see any of these coins ! With iron back, it would identify the coins as iron and grunt. When I set the F5 at minimum discrimination (1), it did the same.

One thing of note: 1988 and 1989 loonies and toonies from any year are exceptions. All detectors identify them correctly.

Thinking that the DD coil could be at fault, I switched to the Detech Ultimate which of course is another DD coil with same results.

I wish I could test in the ground but can't as it's frozen. Perhaps it would make a difference. I don't know. I can just imagine all the recent coins I left behind since I've been using the DD coil thinking they were iron junk.

Any thoughts on this ? Does anybody have recent Canadian coins where they could test with other detectors and the 11 DD coil ? I'm just wondering if detector frequency could have something to do with this. Maybe recent Canadian coins contain iron but then why would the stock coil identify them differently from the DD coil ?

 

[dfmike]

I remember when I bought my F5 and couldn't decide between the DD coil and the stock one. My dealer kept telling me how much he liked using the F5 with the stock coil. Maybe he already knew about this. Just a thought.

 

[jim tn]

I remember John Edmonton, who is from Canada, on the Garrett A T Pro/A TGold forum, comment on the modern era Canada coinage and their metal(s) content. I believe he hunts with the stock DD coil quite a bit with his A T. You might do a search and see what he had to say about i ding Canada coins. Just a thought, anyway, as the Loonies and Toonies metal composite is different. Not a clue myself why a concentric coil would I d them so differently using the same settings? HH jim tn

 

[dfmike]

Thanks Jim. I know you have tested and used many detectors. Have you ever experienced this issue with recent USA coins on what you have used with DD coils attached ? I know that the USA dime passes this test with flying colors. I'll try to find a quarter and nickel that I can test. This really puzzles me.

I find that even with the concentric coil, the ID of recent Canadian coins can be jumpy and audio can register in different tones as well but I don't get the iron grunt that I get with the DD coil.

I wish I had a T2/F70/F75 or a Gold Bug/G2/F19 to test as well just to see if frequency could have something to do with it. I expect not but I'd like to find out.

 

[dfmike]

I managed to find a recent US quarter and a nickel and the detectors with DD coil could easily identify them (repeatable tone, repeatable visual ID higher than iron range). Still struggling with the Canadian loonie, dime, nickel and quarter of recent years though which yield an iron grunt when air tested so iron discrimination makes them invisible. This only happens when the 11 DD coil or Detech Ultimate are used not the 10" concentric which works fine. Any clues as to what could be going on here ?

 

[Mike Hillis]

Hi DFMike,
Concentric coils provide better 'discrimination' than the DD coils. This translates over to target id. Its the nature of the coil designs. When you need very good discrimination you use a concentric coil. When you need very good target separation or increased ground coverage you use a DD coil.

HH
Mike

 

[dfmike]

Hi DFMike,
Concentric coils provide better 'discrimination' than the DD coils. This translates over to target id. Its the nature of the coil designs. When you need very good discrimination you use a concentric coil. When you need very good target separation or increased ground coverage you use a DD coil.

HH
Mike

Hi Mike and thanks. I understand this. I don't know how this could explain why the DD coil on those detectors can properly identify the modern US coins but not the modern Canadian coins mentioned above.

I'm going to have to test these findings in ground to see if I will still encounter the issue when detecting and not just in air tests.

 

[dfmike]

I think I found my answer on Treasurenet. I hope it's OK if I post the link here. Apparently Canadian coins of recent vintage contain steel which is easily shown by picking them up with a magnet. The US nickel, dime and quarter that I have can't be picked up by magnet (I checked this myself). I gather the detector "sees" the iron content of the Canadian coins. They can of course still be detected but with minimal discrimination or in all metal mode only. The toonie is as exception as the center seems non magnetic but the contour is. Whether the detector has the DD or concentric doesn't seem to matter with this coin. It sees the middle part and reports with a high tone and stable numbers.

Perhaps the discrimination properties of the concentric coil can reject the iron content of these Canadian coins and report it's identity with more precision than the DD which identifies them as low conductive iron. I don't know. Just a thought.

treasurenet discussing Canadian coins

 

[Mike Hillis]

Don't your modern coins have an iron core surrounded by a cupra-nickle ring?

HH
Mike

 

[dfmike]

Don't your modern coins have an iron core surrounded by a cupra-nickle ring?

HH
Mike

I'm not sure Mike but it's very possible. That's why I searched and found the link above at Treasurenet with the magnet advice and more info. It's funny because I never thought of trying a magnet on the coins before I read the info. On the F5 with DD coil, all of these Canadian coins (loonie, quarter, dime and nickel) have an ID of 4 or 5 and stick to a weak magnet like glue on glue. Occasionally they will jump to a higher ID and tone. With the concentric it's the other way around. Higher ID numbers with accompanying tone most of the time with the occasional iron grunt.