5 x 10 coil pattern

[1637]

iam using a5x10 detech coil on my whites mxt. what do you think the pattern is at 4 6 8 and 10 inches.i was just wondering how much overlap i should use.all a stock 91/2 coil
thank you guys brad

 

Amazon Forum Fav 👍

Family Maps of Hinds County, Mississippi, Deluxe Edition - Grab it through Amazon!

[Ism]

It really depends on the size of the target, so air-testing would give you the best idea what to expect for the pattern is at depth.

 

[SD51]

I would do an overlap of coil sweeps of one-half of the coils length which is 10 inches. Also, I like to do straight line sweeps of the coil instead of sweeping the coil in an arc. Here's what the Double D coil's magnetic field pattern looks like from a side view.

 

[Carl-NC]

Here is a measured plot from a Fisher DD coil using a US nickel. Most other DD coils will be similar. The left plot is the front-to-rear coverage which is what you're concerned with for overlapping. A shallow target has a pretty flat response but deep/weak targets do not. Even with a 50% overlap (the generally accepted rule-of-thumb) it is very possible to miss a fringe target. That's partly why sites are never completely hunted out.

Also, ignore marketing illustrations of coil patterns. They are invariably wrong.

 

[cudamark]

Find a deep target and pass the coil over it at various spots around the edge to test it's sensitivity compared to dead center. All coils are not created equally.....even the same model from the same company.

 

[ConceptualizedNetherlandr]

Please explain what I am supposed to be seeing in figure 7-17?

 

[Carl-NC]

Please explain what I am supposed to be seeing in figure 7-17?

The "isodetection" lines represent a constant level of target response, in this case a nickel. Similar to how elevation contour lines on a map represent constant elevation. The numbers are the actual voltage deflection in a test receive circuit, so the "1" line is 1 volt of deflection and a flat nickel anywhere along that line causes the same 1 volt response. The "100m" line is 100 millivolts, or 1/10th as strong, and "10m" is another 10x weaker. The left plot looks at the coil front-to-back and the right plot is side-to-side. The dots at the top show where the coil windings are (black=TX, gray=RX) if you were to slice the coil in half.

 

[ConceptualizedNetherlandr]

The "isodetection" lines represent a constant level of target response, in this case a nickel. Similar to how elevation contour lines on a map represent constant elevation. The numbers are the actual voltage deflection in a test receive circuit, so the "1" line is 1 volt of deflection and a flat nickel anywhere along that line causes the same 1 volt response. The "100m" line is 100 millivolts, or 1/10th as strong, and "10m" is another 10x weaker. The left plot looks at the coil front-to-back and the right plot is side-to-side. The dots at the top show where the coil windings are (black=TX, gray=RX) if you were to slice the coil in half.

Thank you for that detail. So the detection response in 3d would look like nested canoes. And of course the response is better in the areas that become fully traversed by the entire detector in the swing path. Hence the need for overlap to achieve maximum, possible detection for a given depth. There is no free lunch you have to religiously cover the entire area.

I have a new question for anyone. Since the response is typically generated by motion of magnetic fields, can a modulated pulse emission do it for a stationary unit? Has this been done? If not why not? Or did I just give a way a huge patent able idea

 

[Carl-NC]

The only reason a target response requires coil motion is that the detector uses filters that block the static response. You can usually bypass the filters using pinpoint mode, then you don't need to keep the coil in motion but you also can't remove the ground signal. Modulating the signal doesn't fix this.