Tuesday, March 31, 2015

3/31/15 Report - Peripheral Sensitivity And Metal Detecting Around Large Metal Objects. Spring Break In Full Swing.

Written by the TreaureGuide for the exclusive use of treasurebeachesreport.BlogSpot.com.

Detectorist On Treasure Coast
Beach Yesterday Near Low Tide

The sand is still piled up.  The nice North wind we had recently didn't do anything good to the beaches.  There were some shells, sea glass and pieces of fossil on some beaches near low tide yesterday.

Bill P., who provided me and the blog with excellent instructions on how to use Muriatic acid to clean cobs back a few years ago was down in the Treasure Coast area and said how disappointed he was to see all the renourishment sand.  That is the way it is now.

I saw this fellow in the picture detecting on feet of newly accreted sand.  He got caught on the Treasure Guide's roving beach cam.

There were a lot of people at the beach yesterday.  It looks like Spring Break is in full swing.  There are a lot of snow birds on the beaches these days.


Bill M. had the following to say.

While researching a ghost town on the west coast of Florida, I found the Florida Memory web site which is filled with old photos, maps and articles about places in Florida from by gone days.

Not sure if you've mentioned this on your blog, but thought I'd share it with you.

I also found the ghost towns link below interesting, but not totally accurate.

Thanks Bill.


Here is a quick video clip showing one Treasure Coast treasure beach from yesterday.


In my most recent post I talked about the importance of knowing the area of target sensitivity for your detector coil and suggested doing air tests to determine the size and shape of the area of target sensitivity for your detector.  Today I'll discuss peripheral sensitivity a bit more.

The area of target sensitivity will be different for different coils and detectors.  The shape of that area will differ and is an important factor.  That is one thing I explained in my previous post.

What I want to talk about today is the far edge of peripheral sensitivity   By that I mean the farthest area out from the center of the coil where things can still be detected.

It might seem surprising to some, but an object doesn't have to be under the detector coil to be detected.  Most small targets do have to be under the coil, but larger objects do not.  You can prove that for yourself.   Try to detect close to a chain link fence, for example.  The fence will give a signal when the coil is inches or feet away from the fence.  The same thing will happen with any large metal object, whether it is a car, rebar in a driveway, lamp post, or whatever.  You can't detect close to those things because of the signal they will cause.

For smaller targets like coins or rings, you obviously don't get such a large signal when the coil is not over the object.   A good hot setup will detect small things under the edge of the coil or out from the edge of the coil just a touch.

Peripheral sensitivity for large objects can be an obstacle.  You won't be able to detect real close to metal lawn chairs or fences.  That provides an opportunity if you can figure out how to work close to those types of objects.  One way to do that is to select the right detector.  Some detector/coil combinations will allow you to get much closer to those types of objects than others.

Another method that will allow you to detect closer is to switch to a smaller coil.  Another is to decrease sensitivity or increase discrimination.

This is one of those situations when you might find that a less expensive or less powerful detector can work to your advantage.

Another thing you can do is to change your sweep pattern.  Sweep your coil parallel to such objects, instead of at and away from those objects.  Instead of walking along a fence, face the fence and sweep the coil parallel to the fence.

Another thing that often helps, is slowing down your sweep speed.

Those things can help you turn an obstacle into an opportunity. 

In a future post I'll talk about methods for making best use of peripheral sensitivity.


On the Treasure Coast the surf is very small these days and the tide is moderate.   On Easter the surf is now predicted to increase to something like 4 to 6 feet.  The earlier predicted eight-foot surf has disappeared from the charts, as is often the case.

Happy hunting,