LawrencetheMDer
Bronze Member
- Joined
- Feb 22, 2014
- Messages
- 1,142
- Reaction score
- 2,979
- Golden Thread
- 0
- Location
- Ohio and Florida
- Detector(s) used
- Minelab Manticore w M8, M11 and M15 coils, , Minelab CTX3030 w 11" and 17" DD coils,
Minelab Excalibur II w 10" coil, Equinox 800 (4) w 11" and 15" coils,
Pointers; Garrett Carrot, Pro Find 35,
- Primary Interest:
- Beach & Shallow Water Hunting
I just finished Moreland’s book Inside the Metal Detector (highly recommended) and it got me thinking of the challenge of detecting small chains. In general, one take-away is if you’re searching for small targets you should use small coils. So I compared with air test the M8 (8”x5.5”), M11 (10.25”x11”) and M15 (15”x12”) Manticore coils on 3 different 14K gold*/ chains. Also looked at the Fisher AQ and threw in a hollow 14k gold band (2.31g) for comparison (hollow bands often are harder to detect).
The setting for the Manticore remained the same for all coils (Sensitivity 24, Beach General, Recovery 4, All Metal) and I only noise canceled between coils. [Why Beach General? On dry sand I have found more targets and more chains with Beach General than Beach Low Conductor! But another story.] For the Fisher AQ, the settings were Delay 7, Sensitivity 8, Threshold 4, ATS 3 and Reject 1 in order to max target detection. I also tried the recommended AQ default settings as noted on each dial, with little difference noted. With the Fisher AQ I listened for any “whispers” of a target to reach threshold. I simply swung the chain back-and-forth in front of the coil along a paper tape measure. A test-retest of each chain and each coil showed a rough estimate of measurement error of 0.5”.
Results are shown in the two Tables below. The top table shows maximum depth while I held the chain claw clasp outside the detection area (size of claw clasp noted in parenthesis, below Table) so that only the chain was detected. The bottom table shows when the chain was folded and allowed the clasp to also be detected.
It should be noted that the Manticore M15 (15”x12”) coil is roughly equivalent in size to the 12.5” Fisher AQ coil based on Moreland’s equation: Effective Size=SQRT((2xW2xL2)/(W2+L2)): The M15 is equivalent to a 13.3” circular coil and the Fisher AQ is 12.5”. With or without the clasp, the M15 coil is about 2” deeper than the M11 coil and basically matches the Fisher AQ coil for the heaviest chain and gold band.
Of course, there are limitations to air testing since it excludes ground, salt and mineralization effects. But these data do make me feel better about using the M15 for most of my beach hunting. Most likely, I am not missing gold chains because of the use of the large M15 coil for better coverage and detection of deeper targets. One caveat here is that all the Manticore coils were run at a Sensitivity of 24, my usual dry beach setting using the M15. In general smaller coils can be run hotter, with higher Sensitivity, than larger coils because larger coils are affected more by ground/mineralization effects as well as salt. So some of the depth differences could be reduced somewhat by running the smaller coils at a higher Sensitivity at least in low mineralized ground.
In general, the M8 coil performed almost as well as the M11 for all chain sizes.
Regarding the Fisher AQ Limited with 12.5” coil, I was quite surprised that the Fisher AQ did not “see” the smaller chains at either the standard settings with background just above threshold as well as settings believed to maximize detection (All Metal, minimal Delay, minimal ATS, minimal Rejection) including listening for any whisper of a target near threshold. One issue that may have affected the AQ is that the chains were swung at a certain rate and it is possible that the chains may have been swung too fast. PI detectors should be swung at a slower rate than VLF detectors. However, during testing of each chain with clasp I varied swing speed and also clumped the chain w/o much notable effect on distance.
To conclude, the Manticore M15 coil does not appear to be less sensitive than smaller Manticore coils to small gold chains in terms of detection depth; indeed, the M15 outperformed the smaller coils. The M15 appears roughly equivalent to the Fisher AQ Limited in terms of depth for gold rings and heavier gold chains and appears superior for detecting small gold chains...Off I go with my M15.
Happy Hunting
The setting for the Manticore remained the same for all coils (Sensitivity 24, Beach General, Recovery 4, All Metal) and I only noise canceled between coils. [Why Beach General? On dry sand I have found more targets and more chains with Beach General than Beach Low Conductor! But another story.] For the Fisher AQ, the settings were Delay 7, Sensitivity 8, Threshold 4, ATS 3 and Reject 1 in order to max target detection. I also tried the recommended AQ default settings as noted on each dial, with little difference noted. With the Fisher AQ I listened for any “whispers” of a target to reach threshold. I simply swung the chain back-and-forth in front of the coil along a paper tape measure. A test-retest of each chain and each coil showed a rough estimate of measurement error of 0.5”.
Results are shown in the two Tables below. The top table shows maximum depth while I held the chain claw clasp outside the detection area (size of claw clasp noted in parenthesis, below Table) so that only the chain was detected. The bottom table shows when the chain was folded and allowed the clasp to also be detected.
It should be noted that the Manticore M15 (15”x12”) coil is roughly equivalent in size to the 12.5” Fisher AQ coil based on Moreland’s equation: Effective Size=SQRT((2xW2xL2)/(W2+L2)): The M15 is equivalent to a 13.3” circular coil and the Fisher AQ is 12.5”. With or without the clasp, the M15 coil is about 2” deeper than the M11 coil and basically matches the Fisher AQ coil for the heaviest chain and gold band.
Of course, there are limitations to air testing since it excludes ground, salt and mineralization effects. But these data do make me feel better about using the M15 for most of my beach hunting. Most likely, I am not missing gold chains because of the use of the large M15 coil for better coverage and detection of deeper targets. One caveat here is that all the Manticore coils were run at a Sensitivity of 24, my usual dry beach setting using the M15. In general smaller coils can be run hotter, with higher Sensitivity, than larger coils because larger coils are affected more by ground/mineralization effects as well as salt. So some of the depth differences could be reduced somewhat by running the smaller coils at a higher Sensitivity at least in low mineralized ground.
In general, the M8 coil performed almost as well as the M11 for all chain sizes.
Regarding the Fisher AQ Limited with 12.5” coil, I was quite surprised that the Fisher AQ did not “see” the smaller chains at either the standard settings with background just above threshold as well as settings believed to maximize detection (All Metal, minimal Delay, minimal ATS, minimal Rejection) including listening for any whisper of a target near threshold. One issue that may have affected the AQ is that the chains were swung at a certain rate and it is possible that the chains may have been swung too fast. PI detectors should be swung at a slower rate than VLF detectors. However, during testing of each chain with clasp I varied swing speed and also clumped the chain w/o much notable effect on distance.
To conclude, the Manticore M15 coil does not appear to be less sensitive than smaller Manticore coils to small gold chains in terms of detection depth; indeed, the M15 outperformed the smaller coils. The M15 appears roughly equivalent to the Fisher AQ Limited in terms of depth for gold rings and heavier gold chains and appears superior for detecting small gold chains...Off I go with my M15.
Happy Hunting
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I have 4 Pi's -Whites , never bought an AQ , in closing I will say , I like the 9 , but I would compare depth tests , stability in Salt before I would toss the stock M-8 aside, happy hunting. PS For a 1 inch coil size difference & 300 clams without a lower rod , that choice Digger is yours's only to make 
