Coil Design, Separation, Recovery Speed, Sweep Speed, Unmasking- Do You REALLY Understand Them?

[Critterhunter]

I threw together a small tutorial on these topics in the Sovereign forum. You might be surprised to find that things you always assumed or confused were not true, and how they really do or really don't effect the other. For instance, did you always believe that a fast recovery speed is what gave a machine good separation? I know when I really sat down and thought about it I had to correct a few assumptions in my mind that I just assumed without thinking it over carefully. Even if you're a seasoned vet you might find what you always thought was wrong about certain things. Enjoy and feel free to offer a differing view...

http://www.findmall.com/read.php?21,1168161

 

[UK Brian]

I've no problem with most of your comments though you have continued to promote the old propaganda that was introduced by one of the first manufacturers to widely introduce the double D coil ie that concentric's have a cone shaped detection pattern while double D's have a nice wiper effect.

Both are incorrect. Most concentric's have a nice squashed balloon pattern which is very different from what comes to mind when inverted cone is mentioned whilst some coils even have a field that looks like a child's drawing of a spikey Christmas tree that's been inverted.

Another thing that could be considered if you extend your report to other machines ie away from BBS and FBS, is at what point the advice to sweep "slow and low" is the worse thing you can do.

Regards Brian

 

[Larry (IL)]

I have to agree with you Brian on both accounts. "Slow and low" works well for separating trash and target, but many detectors are made for a faster swing for optimum depth.

 

[Critterhunter]

Of course the article is tailored more to information for Sovereign owners because that's what it was originally intended for. After I wrote it I decided there was enough general information to be of interest to other detector users as well. The fast/slow sweep speed criteria for different machines is also covered in the second message, enough to warn people with fast sweep machines about the problems that may occur if they try to gain the benefits of a slow recovery/sweep machine by slowing theirs down as well. Namely, loss of target quality or depth can result from slowing down a fast sweep and/or recovery machine and even if that's possible the benefits might out weigh the costs. Those advantages are not as easily obtained with a fast machine to mimic a slow one, where as it's very possible to gain the advantages of a fast machine by using a slow sweep/recovery machine properly, mainly by keeping the sweep speed slow enough to allow the unit to reset and "see" between the targets. A lot of people believe recovery speed is what makes separation happen. That's not at all the case. It only allows you to sweep real fast without targets being blended together.

As for the signal dynamics of concentrics and DDs, it is true that many concentrics have more of a half circle or "egg" shaped signal than describing it to be more like an ice cream cone. However, that sort of comparison better illustrates why a concentric can have certain disadvantages to a double D. It still stands that the detection line of a DD coil from tip to toe has more uniform and equal depth across the entire coil length than a concentric. Separation ability of most DDs is also more useful at any depth where as a concentric gets more use of it's field to do this at its deepest part of the detection field. It also is still true that concentrics do not put up as well with ground minerals, costing depth or producing "washed out" or degraded target quality when the minerals present are high enough. A DD's ability to not take in as big of a picture of the ground allows machines to be easier to ground balance as well as decreasing the chance that the more intense ground filtering required to remain stable of a concentric is also costing you target quality or depth.

As I said, there is still great debate among detectorists (including us! ) as to exactly what the benefits of various coils and functions of a machine are, as well as the negatives. I look forward to hearing more differing opinion on these matters to continue the exchange of ideas.

 

[Critterhunter]

Made a mistake where I said loss of target quality or depth can result from slowing down a fast sweep and/or recovery machine and even if that's possible the benefits may outweigh the costs. Meant to say of course that the costs probably will outweigh the benefits, if any are even possible.

Wanted to also add that a DD's ability to not take in as big of a picture of the ground allows machines to be easier to ground balance as well as decreasing the chance that the more intense ground filtering required to remain stable of a concentric is also costing you target quality or depth. Remember that on most VLF detectors the target's signal must first stand out from the filtered ground signal. Being "drowned" in that matrix more on a concentric means there is more chance for the depth or target signal to degrade.

 

[Jackpine Savage]

Good point Brian,

In the old Fisher line alone there are 2 machines, the CZ's and Coinstrike, that are polar opposites when it come to depth, iron handling and getting a decent TID. They are fairly equal in picking out deep targets in iron but require totally different sweep speeds to get best results.

Tom