Wrap

[aloldstuff]

Okay so I have heard wrap. Just what exactly is it and can it be eliminated??

[CyberSage]

Al,
Here is the way I see it. Wrap is a target that gives a skewed VDI response in such a way that the detector shows it to be at the extreme opposite of it's actual VDI. Think of the Whites VDI scale of -95 to +95 being circular in nature instead of linear. This would put -95 and +95 right next to each other on the wheel.

http://www.fielddepth.com/vdiwheel.jpg

This illustration is a link from Jeff Foster at www.fielddepth.com (http://www.fielddepth.com)

The most common form of wrap is when a nail, wire, or blob of iron jumps from the extreme negative to the positive area in the 90's, as noted in the above illustration. If your tone hunting these responses will be high pitched, short, and cut off in their audio response. Just the opposite can occur with a high conductive target. The normal VDI can be exaggerated upward until it jumps to the negative side in the low 90's.
There are a few things that can cause this behavior. I believe a target that is on the fringe of your coil field, whether it is due to just raw depth, or just lower sensitivity setting in a high EMI environment, will trigger this exaggeration. Soils with a moderate to high mineralization strength, and improperly set filters can also aggravate the situation. I have seen this behavior with the MXT, DFX, V3/V3i, but it was not until the Correlate mode on the V3 that we had a way to really deal with it effectively. We actally have a setting called Wrap lol , and Span to deal with this. The Correlate mode on the V3/V3i looks for two frequencies to agree on a response from a target. The criteria for determining whether two frequencies agree is how close the VDI response matches. This how close condition is determined by the Span Limit. The larger the span limit the more accepting the response trigger is to the VDI response of the target between those two frequencies. The Wrap Limit allows the Span setting to extend around to the negative side. Deep targets can cause the higher two frequencies to Wrap around to the negative side. I have even seen all 3 frequencies wrap in high EMI scenarios, or with improperly nulled coils. These settings are among the most powerful options on the V3/V3i. By tightening your span setting you can eliminate the deep iron which has a broader response pattern, and still hit those high conductive targets which have a narrower response pattern. Keep in mind that Higher frequencies wrap sooner than lower frequencies, and visa-versa on a wrap from the low side (nail, etc.) I know this all sounds complicated, but it's worth it in the end, as I believe it is one of the key factors in getting great depth with the V3/V3i.

Jack

[aloldstuff]

Jack, thanks for indepth explanation. Can I conclude that when I get a wrap situation that there might actually be good target down below?

[Digger]

Thanks Jack, thats going in my folder too. |:cheering:

[CyberSage]

Jack, thanks for indepth explanation. Can I conclude that when I get a wrap situation that there might actually be good target down below?


Al,
If your getting consistent hits at 90 degree angles it is worth digging. Deep Iron will typically have an off center pinpoint to where the motion mode focus was. It will be much lighter in VCO response compared to a coin at the same depth. Dig a few, and see what is causing the response. When you dig a few coins at depth it will fall together for you. If you dig a nail, toss a copper penny in the hole before you cover it up. Pinpoint the penny and hear the difference in response compared to the nail you just dug. Don't worry about motion mode response from your freshly buried coin, it won't be accurate, but the pinpoint behavior will be true.

Jack