What Are Whites Df Coils Classed As Please ??

[Glenn in CO]

19 hours ago, Steve Herschbach said:

I decided to go to the source - the Dual Field patent.

"A new dual field search coil for pulse induction metal detectors has multiple coplanar wire coils of different diameters connected in series with the output of a pulse source, overcoming the loss of target size resolution associated with a single coil search loop. Small objects are sensed by an internal small coil and larger objects are sensed by the larger outside coil, and the overall depth of target sensing remains similar to that of a single coil construction. The smaller coil is isolated from the pulse source by the inductance of the larger coil and will ring at a frequency determined by its own parameters. To prevent the smaller coil from ringing, a second damping resistor is connected across the terminals of the smaller coil at the junction of the large and small coils making up the modified search loop."

So my question is if I'm reading this information right, does the smaller coil achieve the same depth as larger outside coil?

If that is true would the 7.5" Dual Field coil have the same depth as the 12" Dual Field coil? I'm basing these questions on coin size targets.

[Steve Herschbach]

2 hours ago, Glenn in CO said:

So my question is if I'm reading this information right, does the smaller coil achieve the same depth as larger outside coil?

If that is true would the 7.5" Dual Field coil have the same depth as the 12" Dual Field coil? I'm basing these questions on coin size targets.

No, I’m not sure how you are reading that into it, especially if you read the full source article. The max depth on coin size targets is determined by the outer coil, a coin being a large target. The inner coil enhances sensitivity on stuff like ear rings and small gold nuggets.

[Glenn in CO]

19 hours ago, Steve Herschbach said:

Small objects are sensed by an internal small coil and larger objects are sensed by the larger outside coil, and the overall depth of target sensing remains similar to that of a single coil construction.

Whoops! I guess I was reading that statement as the smaller coil would achieve the same depth as outside larger coil.

[Steve Herschbach]

That would be nice - you would not need the outer coil. 

[HardPack]

I assume the “folded mono coils” are also in series similar to the White TDI mono Dual Field but in a figure eight design folded back on itself with the smaller loop placed to the interior. The location of figure eight coil crossing would most likely be located at the heel of the coil.  

Both the waterproof White TDI 7.5 DF coil and an the after market waterproof 5x9 folded mono coil are good prospecting for tools for tight spaces and for those hard to reach partially submersed waterfall rock shelves that intersect the stream “V” channel. A better design would be a simple 5x9 waterproof mono coil with a sensitive front toe/tip. (That was for the Garrett Axiom engineers).
 

[Jim in Idaho]

From what I see, that is correct. But, the interesting thing is you can get the two magnetic fields working together (adding), or contrary to each other, depending on how the "fold" was done, if I'm looking at this correctly. IMHO, the 5 x9 FM was nothing special as far as sensitivity goes.

Jim

[HardPack]

I agree but the size & shape serves it purpose.