Friday, August 29, 2014

8/29/14 Report - Detector Test Using Silver Cobs in High EMI Environment. A Couple Tips For Detecting Junky Sites.

Written by the TreasureGuide for the exclusive use of

Four Treasure Coast 1715 Fleet Beach Cobs.  Three Half-Reales and One 1-Reale.

There are times when it is a good idea to try something new.  If you try something new there is a good chance that you will strike out, but you very well might learn something valuable in the process.

When you try a new site, the first visit might not be much more than a scouting trip or site preparation.   Too many people give up on a new site too quickly.  They do a little detecting and decide that there is nothing there or that the site is too junky.  Before giving up, they should analyze the situation, test different areas, and find out where things used to be and what might be there.

Sometimes on your first visit you'll be accomplishing a lot if you simply remove the surface trash.  That can be true on either a beach or inland site.

For trashy sites you might want to use a magnetic rake.  They are made for post-construction clean-ups, but you can use them for pre-detecting cleaning.  They come in a variety of types.  Below is a link that shows a few of those types.

Using a magnetic rake can really help you prepare a trashy site.  Trash can mask a lot of good targets so it is good to get rid of a lot of it.

And it is always a good idea to have a magnet like the one shown in the following video when you have to deal with nails and things like that.  I sometimes tape a magnet like this one to the handle end of my scoop.

This procedure works very well.  You can waste a lot of time searching for a small screw or bit or iron. 

After pinpointing an iron item, pick it up with the magnet.  As you can tell if you carefully listen to the video, you can hear when an iron object gets picked up by the magnet. 

I've been noticing a lot of good potential land detecting sites lately. Keep your eyes open as you drive. 

I did some new tests.  I used the four silver cobs shown at the top of the post.  Left to right they weight about 0.4 grams, 0.5 grams, 0.6 grams and 2.0 grams.  All four are very much under weight for their denomination.  That is not unusual for beach cobs.

The first part of the test was conducted with the Ace 250, an inexpensive detector with target ID.  I've talked about that detector in the past.

The setting was a front yard where there is considerable electromagnetic interference from power lines, underground cables, etc.

I simply put the four cobs on the ground (didn't bury them) spaced apart about a foot.

When using the Ace all four cobs were easily detected, mostly being identified as nickels.  Two cobs jumped a little on the target ID - one one way and the other the other way. 

Here is where it starts to get interesting.  You would assume that the silver in all four cobs is of similar purity.  I know that might not be exactly the case, but I would not expect them to vary a lot.

But I got a hint of something interesting in this part of the test.  The heaviest cobs did not always give the best signal.  And the cobs presenting the most surface area did not always give the best signal. 

Using the Ace, the third cob from the right occasionally jumped into the pull tab range, while the second cob occasionally jumped from the nickel to foil ID range.

I repeated this process many times with different sweep speeds, slightly varying the height of the coil, and changing the centering of the coil.  Same results.  The smallest and largest of the two cobs without exception were identified as nickels.  Only the other two differed, one towards the upper end of the range and the other towards the lower.

I did not take this too seriously yet.  I then tested the same cobs with two other detectors.  In another post I'll discuss how that added to the evidence found in this part of the test.

What I did conclude from this first test is that it is not always the larger target or the target presenting the most surface area that creates the loudest signal.  Bigger is not always louder, even when the metal is the same (or nearly so).  These conclusions were supported using two other very different detectors.  Like I said, more on that some other time.

Another thing I concluded is that ( and not taking depth into account) the Ace worked as well as the Dual Surf PI and Excalibur for detecting these small surface cobs in this environment.  The Ace, which was operated with the default settings (not maximum sensitivity) was not as much affected by EMI and did as well as the other two detectors.

One thing I want to reiterate is the importance of testing detectors on specific targets and under specific circumstances.   Here you have a case where an inexpensive detector that some call a toy worked as well or better than much more expensive detectors. 

The results might change if the cobs were buried at depth and for a time.  I don't know that yet.

On the Treasure Coast today we had a 2 - 3 foot surf.  Tomorrow the surf is predicted to be down around one foot.

We only have one tropical wave right now, and it is down below the islands and apparently headed towards Central America.

That is all for now.

Happy hunting,