Question on Coil size: 6" vs. 11" depth

[UncleVinnys]

If the same amount of power goes into a 6-inch coil as an 11-inch coil, does that mean the field density penetrates deeper?

I have two Double-D coil for my Minelab.
You would think the larger coil would go deeper, but if the same energy is pouring into the 6" coil,
and being double-D, maybe the output gets squeezed into a deeper spade-like configuration.
I don't know.
Think we need a physics person or antenna engineer.

 

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[jcc]

There is a whole lot of ground to cover here.

I recommend "Inside the Metal Detector" by George Overton and Carl Moreland.

The answers you seek lie in Chapter 5.

 

[eman1000]

Vinny I'm not an engineer either but it has been my personal experience that the coil size usually corresponds to approx. depth plus an 1". There have been a few machines I have owned that beat this rule and the Equinox is at little better in this department as the 6" coil punches pretty deep maybe 8" give or take and the 11" coil is good to 12" ..maybe 13" on a US Quarter.

Now I have the Deus with a 9" HF coil which has it's own power and it can nearly hold its own in depth to the 11" coil on the NOX. The 9" HF Coil is good to about 11-12" give or take an 1"

Not everything is about depth though as I almost never run wide open (exception would be a farm field) - The real advantage to the 6" coil is getting good targets separated from iron or trash and the NOX 6" is probably the best small coil setup on the market. I still use an 5.3" coil on my whites but I have to admit it is not as good as the NOX as it is only good to about 6/7" and it doesn't separate trash as well. Of course the down side is your can't cover much ground with a 6" coil and the NOX 6" is very small.

Big open field with little iron or trash larger coil setup is ideal but a trashy park or old home site the 6" coil will find the goodies.

I would imagine it has something to do with how much copper is wound in the coil and the diameter of the coil would create a larger "arc" or search area in the ground thus penetrating deeper.

 

[UncleVinnys]

Thanks for the replies.
eMan: Yeah, I was kind of hoping (against logic) that somehow the concentrated field of the 6" would gain an advantage.
Here in California, depth is not quite as important as on the East coast, where states have a longer history.
Here it's rare to find any coins deeper than 3-4 inches.

 

[Terry Soloman]

If the same amount of power goes into a 6-inch coil as an 11-inch coil, does that mean the field density penetrates deeper?

I have two Double-D coil for my Minelab.
You would think the larger coil would go deeper, but if the same energy is pouring into the 6" coil,
and being double-D, maybe the output gets squeezed into a deeper spade-like configuration.
I don't know.
Think we need a physics person or antenna engineer.

The rule of thumb is that the 11" DD coil will cover more ground, and increase depth penetration 5-15 percent depending on setup and soil conditions. It also sucks MORE battery power, because is has more copper windings than the smaller coil. Bigger coil, more power, more depth, but may miss targets smaller than a Trime.

 

[SanMan]

Back in the day the diameter of the coil was about,
(depending on conditions and target size), equal to the depth of detection.

Then progress came along and you got a bit more.

Good example is the hockey puck for the AT Pro.
Very hot, you need to throttle back on it in trashy spots.
If you don't, it sees too much and it becomes frustrating.

Now a days there are a good many coils that punch above their body weight.

Of course, the target has a great deal to do with depth,........

A dime, a half dollar coin, a padlock, a handgun, etc.