Delay of a dual field Coil vs basic mono coil, (another question for Reg)

[Roughwater]

Hi Reg,

My question is: do you a think a dual field coil may have a delay advantage compared with a similar built mono of the same size?

I ask this because prior to stuffing my 1M coil in PVC I tested it at your suggestion and when folded into a dual field configuration the useable delay improved much more than I would have anticipated.

Thanks a ton in advance,

Terry

[Reg]

Hi Terry,

To be honest, I have not tried to compare the delay feature of similar size coils, with one being the dual field design.

Now, when I built my first dual field and left the coil in a typical mono coil and then later folded some of the coil back inside, it appeared the coil got faster. I didn't try to actually measure anything at the time though. I really need to do that at some point in the future.

The dual field that I built that I like the best is one where the inner coil is simply a skinny narrow inner coil. This minimizes the extra size but still gives me the small coil advantage for detecting small objects.

If you look at Hays coil housings and focus on figure H you will see the only way to build an inner coil that will work is to make a narrow elliptical type coil to fit the inner area. Here is a link to the Hays housings if you haven't looked at them.

http://www.hayselectronics.com/parts.htm

On other point, keep in mind that the dual field using one larger coil and making two smaller coils out of it is not the same as the dual field built by Whites. They use two separate windings but put them in series. They also have an additional internal damping resistor across one or more of the windings. I really am not sure of the exact design so I can't say for sure. Hopefully, once the patent is out, we will know more.

Reg