Written by the TreaureGuide for the exclusive use of treasurebeachesreport.blogspot.com.
A few days ago (/10/17) I talked about the cone of sensitivity for different metal detector coils. I showed that for some coils, the area of sensitivity is more cone shaped. For a cone-shaped coil, the maximum depth is obtained when a target is under the center of the coil. You get less depth when a target is out near the edge of the coil.
The illustration above shows the theoretical cone of sensitivity for two different types of coils - a concentric coil and a DD coil. According to what you will typically read or hear, the area of sensitivity under a DD coil will not be as sharply cone-shaped as it will be for a concentric coil. When looking at the area of sensitivity from the side you can see that it is more blunt from a side view. The area of sensitivity is supposed to be narrow for a DD coil when viewed from the front or back.
The depth you will get with a DD coil for a target under the center of the coil will be similar to the depth that you get when the target is near the edge of the coil. The importance of that is that you will be getting greater depth under a wider span of the coil, making overlapping of sweeps less important because you are getting good depth under the entire area of the coil (front to back). When using a concentric coil, failure to overlap sweeps would mean missing more deeper targets that fall closer to the front or back edge of the coil where you get less depth.
I am not one to go by theory or what everybody says or even by what the manual says. I test things out.
In my 6/10 post, I encouraged you to use a test object to map out the area of sensitivity for your coil and detector. Doing an air test, pass a test object under the center of the coil and see how deep the object can be detected. (That is how most air tests are conducted.) Then pass the object out towards the edge of the coil and see how deep the object is detected, and then do the same thing with the object farther out near the edge of the coil. You will get a good idea of how much depth you will get under the center of the coil and farther away from the edge of the coil.
Mostly we talk about the area of a coil's sensitivity from front to back. DD coils are often said to have a narrower area of side to side. That is supposed to result in better target separation. You should be able to distinguish between two targets that are beside each other.
With my tests I definitely found that one detector/coil combination had a much sharper cone shaped area of sensitivity than another. As expected the concentric coil had a sharp cone shaped area of sensitivity, and the DD coil had a more blunt shaped area of sensitivity, as shown in the illustration. I did not, however, find that the side to side area of sensitivity was narrow. It seemed about as blunt as the front to back sensitivity. So much for what the manual says. Although that test did not correspond to what the manualsaid, my tests corresponded very well with what I experienced in the field. This particular detector/coil combination does not provide good target separation even though it involves a DD coil. Targets sound big. And a bunch of small close targets sound very much like one big target. How much of that is electrical engineering and physics and how much of it is psychosensory, I don't know, but that isn't important to the detectorist. The important thing is how you perceive it in the field.
My main point is to experiment so that you really get to know your detector and how it responds. Get to know both its strong points and its weaknesses. Read the manual, but test everything out for yourself. You might find that what you have been reading or hearing does not seem to be true for your situation.
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| Source: See link below. |
MACKINAW CITY, MI - A 250-year-old lock was discovered at Colonial Michilimackinac earlier this week.
Staff at the historic fort and trading post in Mackinaw City discovered the intact, 2.75-inch long and 2.25-inch wide brass artifact while excavating a fur trader's home on the site.
Lynn Evans, curator of archaeology at Mackinac State Historic Parks, said the piece was likely used to lock a small trunk or chest sometime between 1760 and 1770. The lock is a rare find, even for a place full of hidden treasures like Fort Michilimackinac...
Here is the link for the original article.
http://www.mlive.com/news/grand-rapids/index.ssf/2017/06/revolutionary_war-era_lock_une.html
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Some of you will consider this off-topic. Thats ok.
BAE, a British company that has been widely criticized for sharing communications surveillance software to countries with human rights abuses. The software is capable of tracking virtually ALL computer communications.
I saw a TED talk, which I wish I could find again, on Evident, a software package about which it has been said, "You'd be able to intercept any internet traffic," a former employee told the BBC. "If you wanted to do a whole country, you could. You could pin-point people's locations based on cellular data. You could follow people around. They were quite far ahead with voice recognition. They were capable of decrypting stuff as well."
I just think a computer user should be aware of the digital environment they inhabit and more generally the world they live in.
Treasure hunters used to be very much interested in treasure maps, codes, covert activities and the like. Doesn't seem to be the case so much anymore.
Watching the hearings on TV, one thing that impressed me is the number of things that they feel they have to keep secret from the citizens of the country. Very much like archaeology, but a byproduct of terrorism instead of looting.
Here is one link if you are interested in this type of thing.
http://www.bbc.com/news/world-middle-east-40276568
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On the Treasure Coast we have more smooth surf for days or weeks. The tides are pretty good now, with some nice low tides.
Happy hunting,
TreasureGuide@comcast.net
