Written by the TreasureGuide for the exclusive use of the Treasure Beaches Report.
A couple days ago I talked a good bit about gridding. I said the actual coverage area of a grid is like a block of Swiss cheese. By that I meant the coverage, despite your best efforts, will be spotty. There will be spots where the coverage is not as complete. There will be areas where the sensitivy is not the best. In short, there will be holes in the coverage.
Just because your focus on owning precious metals is on the potential appreciation in the value of the metal content does not preclude you from also being a collector. There is a wide variety of gold, silver, platinum, and even palladium coins available at bullion prices, but they could be acquired to form a collection.
Perhaps the most popular such collection is assembling a year set of U.S. Silver Eagle Dollars...
Among our customers, there are many silver stackers who are always on the lookout for different designs of 1-ounce silver rounds or rectangles...
For those purchasing gold, there are some who accumulate year sets of any size of the U.S. Gold American Eagles (depending on someone’s budget). But another popular variation is to collect different bullion-priced gold coins from as many different nations as possible...
There are many things that can cause missing areas. For one thing, your sweeps won't always be perfect. Small and deep targets that might produce only slight signals can be missed or lost in other sources of noise. There can be attention lapses, that combined with noise, results in misses. And there can be interaction between objects in the ground - sometimes one overlapping with another or two or more being in very close proximity resulting in masking. That is just a brief summary.
As you sweep your coil, the metal detector is constantly adjusting to variations in the soil. Soil mineralization occurs when minerals like iron oxides, salts, or other conductive/magnetic materials are present in the soil. These minerals affect the detector’s electromagnetic field, producing background signals that can mimic metal targets or mask real ones. This reduces detection depth, increases false signals, and makes target identification harder. Metal object (trash or treasure) in the ground does the same thing. There are therefore shadows or holes in coverage - some more complete than others.
Here is an illustration that helps make that clearer. It is from the online Manticore user's manual. It is about recovery speed. If a detector signals in response to one target (or a source of noise, such as mineralization), the signal persists in time for a short time. That can cause the next target to get lost in the signal if the first signal has not ended by the time the next begins.
Recovery speed is adjustable on the Manticore and other metal detectors. Here is a diagram from the manual to illustrate the effect.
The diagram shows, first, how a slow recovery speed with cause something like a screw to create noise that could overshadow that of a nearby coin. And moving down the diagram, how a faster recovery speed results in shorter duration signals and better target separation.
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But continue down the diagram. recovery speed interacts with sweep speed. And a higher recovery speed, while helping to reject ground noise, will also reduce detection depth. People are not always aware of the interactions and effects. There are tradeoffs. There are times when rejecting ground noise (a good thing) results in reduced depth (not so good), such as with the higher recovery speed. You might not be aware of all the effects, but you will be giving up one thing or the other and need to make a good decision. Which do you need at this or that situation? It is a strategic decision. But no matter which you select, you are giving up something. The result will be what I called a "hole" in your coverage. Be aware of the holes in your coverage. And take that fact into account.
One way to reduce target masking is by sweep sweeping in more than one direction. In the top diagram, the screw comes before the coin. That is if you are sweeping left to right. If after gridding in one direction, north to south for example, you can then go over the grid area another time in a different direction. Don't be surprised if you pick up new signals that you didn't get the first time, especially if you have a target rich area, which would often be the case if you decide it is worth gridding. I'd only grid if I believe there was either a target rich area, or the possibility of a very rich target. It can be either because of the quantity or quality of expected targets.
When you change the direction of your sweep on a second pass, you can accomplish several things. Besides eliminating some cases of masking, you can also hit areas missed or covered poorly by an imperfect sweep. Soil mineralization can also be reduced in some cases by simply changing the direction of your sweep.
I remember a fellow using a high-level gold detector costing a few thousand dollars (maybe twenty years ago) telling me he got better sensitivity sweeping parallel to the waters edge. He mentioned it possibly being due to the earth's magnetic field. But that wasn't the reason.
The salt mineralization and set/dry sand lines will run parallel to the water as the waves come and go. You minimize that effect by sweeping in the direction of those lines rather than over them. Sweeping across those wet/dry lines and the abrupt changes in mineralization causes the detector to have to adjust to all that. The result is reduced sensitivity to targets that the detector has to separate out from the noise.
Notice in the Minelab manual, that it says a good swing rate is two to three seconds for an entire swing that goes both ways. I'd guess that most people tend to swing faster than that. In one old post I told how you can test for the best swing rate for specific targets. Do a ground test with the types of target you are more interested in, vary your swing and observe the response. Notice how the signal varies. Identify the sweep speed that gives the best signal and most depth of detection in the type of ground. I recommend doing that at the area you will be working. You can find the best sweep rate with the specific type of ground you will be working. A ground test is also good since you'll get the feel of the correct speed. Practice it a little so you get the feel.
Similar to sweeping parallel to the water line is sweeping parallel to other features. For example, if you want to detect near a metal fence, you will do better sweeping parallel to the fence instead of towards and away from the fence. Same thing with a plowed field. You'll generally do better sweeping parallel to the rows. And that is basically for the same reason.
I won't go into all my recommendations for ground or garden tests again, but the type of object you most want to detect should be used and it is best if the target is buried in the type of soil or sand you'll be metal detecting.
Don't think there are no holes in your coverage. You might want to fill them instead.
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Just because your focus on owning precious metals is on the potential appreciation in the value of the metal content does not preclude you from also being a collector. There is a wide variety of gold, silver, platinum, and even palladium coins available at bullion prices, but they could be acquired to form a collection.
Perhaps the most popular such collection is assembling a year set of U.S. Silver Eagle Dollars...
Among our customers, there are many silver stackers who are always on the lookout for different designs of 1-ounce silver rounds or rectangles...
For those purchasing gold, there are some who accumulate year sets of any size of the U.S. Gold American Eagles (depending on someone’s budget). But another popular variation is to collect different bullion-priced gold coins from as many different nations as possible...
Here is that link.
Nothing that will affect our beach coditions going on right now.
Purchasing Bullion as a Collection - Numismatic News
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| Source: nhc.noaa.gov. |
Nothing that will affect our beach coditions going on right now.
Still nothing more than about a two-foot surf for another week.
Good hunting,
Treasureguide@comcast.net