Written by the TreasureGuide for the exclusive use of the Treasure Beaches Report.
 |
| Clad Eisenhower Dollar and Kennedy Half Dollar Coins Used in Tests Described Below.. |
I previously tested the metal detector response to silver and clad half dollars. I found there was very little, if any consistent discernable difference between the detector response to the 90% silver and clad half dollar coins. Now I'll look at coins of the same composition but different sizes. I'll use the 1971 clad Kennedy half and a 1972 previously dug Eisenhower dollar. Below are the specifics on both coins.
1972 D Eisenhower Dollar
Clad Composition
Mintage: 92,548,511
Minted at: Denver
Designer - Engraver: Frank Gasparro
Metal Composition: 91.67% Copper - 8.33% Nickel
Diameter: 38.1 mm
Mass / Weight: 22.68 grams
I calculated the surface area to be 1133 mm.
1971 D Kennedy Half Dollar
Clad Composition
Mintage: 302,097,424
Minted at: Denver
Designer - Engraver: Gilroy Roberts
Metal Composition: 91.67% Copper - 8.33% Nickel
Diameter: 30.6 mm
Mass / Weight: 11.34 grams
What This Coin Looks Like (Obverse, Reverse, Mint Mark Location, Special Features, etc.):
So the half has 65% of the surface area of the dollar coin, and the mass is of the Kennedy half is one half that of the dollar coin.
I used the Equinox 600 to begin with and used the factory presets again. The coins were laid flat on the sand, the same as during the previous experiment.
The Kennedy half showed up as mostly a 33 on the conductivity readout, which is consistent with what was shown by the previous test using the same half dollar coin. Depth on the half was about 9.5 or ten inches, which is less than on the previous test in the same location. I believe this is due to ambient electrical interference. More on that later.
The Eisenhower dollar, which has twice the mass and a presents a lot more surface area to the metal detector, was detected at about the same depth as the half dollar coin. So - no significant difference in depth for the two coins. That was surprising to me. Wouldn't you expect a larger heavier coin to be detected significantly deeper than a much smaller coin of the same composition? But in these field conditions, that didn't happen. Any difference in depth was very small.
I stood the half on end again, as in the last experiment. When sweeping across, or at nearly a 90 degree angle to the edge of the coin, the conductivity numbers were very similar to those produced by the same coin laying flat. Depth was significantly reduced for the standing coin though. Sweeping in the same direction as the edge of the coin, produced conductivity numbers of around 14. So when sweeping in one direction across the standing coin, one direction produced conductivity numbers centering on 33 or 34, which the other direction produced numbers centering consistently around 14. That pretty much replicates what I found during the previous experiment and shows once again the position of the coin can affect the signal in two ways: First, depth was reduced, and secondly the conductivity numbers can be very different, depending upon the postion of the coin relative to the coil during the sweep.
On to the dollar coin.
The Eisenhower dollar laying flat produced conductivity numbers of mostly 36 and 37. The difference seemed to me to be consistent enough and great enough to be useful in discriminating between the two coins in the field. I don't know why you would need to do that, but the fact the conductivity numbers were different between the two coins having the same composition shows the importance of size when it comes to determining the conductivity numbers.
I don't care what the numbers are supposed to indicate. I'm interested in empirical field results, and that is what I am getting in these tests.
I increased the sensitivity from the factory preset setting up to 25 on the Equinox. When I increased the sensitivity to 25, I got a lot of noise from electrical interference in the environment..
Sensitivity is sensitivity - both to targets and ambient electrical interference. The increased sensitivity in this case resulted in so much noise that it was very difficult to pick out the target signal.
After returning the Equinox to the factory presets, I then changed the operating frequencies on the Equinox. I'll just mention two to illustrate what I saw even though I actually looked at the entire range of available operating frequencies. Using five kz., there was a lot of audible noise. When I used 15 kz., there was no noise, but the loss of depth was very significant. Overall, I found the factory preset multi-frequency best.
I also tested the inexpensive Garrett Ace. Again, it provided much less depth than the Equinox, but clearly and flawlessly identified the half and dollar coins on the ID meter. Totally consistent and accurate.
I heard no noise when using the Ace in the test area in either the coin or all-metal modes. There are always tradeoffs. Ease of operation in a starter detector is probably a good idea, even if it means a loss of depth. The Ace was used at maximum sensitivity. From past experience, I know it will produce noise if used under powerlines though. So there are times when even the Ace is vulnerable to ambient electrical interference.
So one thing I learned today is that for the two coins of the same metallic composition but different size, the Equinox was able to provide information that would help the detectorist to discern between the dollar and half dollar coins. The conductivity numbers were not hugely different, but I think enough to make the discrimination, if you were to, for some reason, want to discriminate between a half and dollar coin. I personally don't know why you would want to do that, but it does tell something about how the metal detector works, particularly what factors influence the conductivity numbers displayed.
I was surprised by the little difference in depth on the two coins even though one was a lot bigger and heavier than the other.
I'll test other coins and other metal detectors in the future. I've only conducted a few quick tests so far, but have already been surprised by a few things and have a learned a few things.
The depths I've been seeing are probably less than would be obtained on the beach away from many sources of electrical interference. You might also expect greater depth on coins that have been buried for a while. I've discussed many of the limitations of air tests and test gardens in the past and much of that applies to what I am doing now.
---
Did you hear they were telling beach-goers in South Carolina to turn in debris that might be from the exploded Chinese baloon? Wasn't there a better way to do that?
---
 |
| Source: MagicSeaWeed.com |
Expect a bigger surf tomorrow.
Good hunting,
TreasureGuide@comcast.net