PI, Oval Coil

[Bob_T]

I made a quick oval coil wind just to see what it would be like.
As an experiment grabbed a 7" round wound mono coil, not much to look at as I used extra coil wire I had around and spliced them together to make this coil.
Took that 7" coil prior to adding the spiral wrap and bent it into a elliptical configuration. Then spiral wrap and then foil tape. Attached some coax and then turned on my PI.
Air test depth wise, no different than the 7" round. What I did see, the detection pattern narrowed and lengthened.

It would be interesting, to me at least, to also make a smaller round coil with the same diameter as the minor diameter of the oval coil and document the real world response/performance of all three coils.

Welcome to the forum Bob.

Thanks Sven, as a beginner I feel a bit uncomfortable here among the gurus and I hope I'm not dragging the discussion down to a lowest common denominator level.

- Bob

[nelson]

Dear friend Gary

First of all i hope you and Janne are fine.

Second, i will like to ask you if you can build for me an oval coil to be used on a Surfmaster detector.
The idea is to get a better performance on this detector for small metals like coins and why not some gold nuggets.

Wishing you the very best.

Nelson

[bbsailor]

I made a quick oval coil wind just to see what it would be like.
As an experiment grabbed a 7" round wound mono coil, not much to look at as I used extra coil wire I had around and spliced them together to make this coil.
Took that 7" coil prior to adding the spiral wrap and bent it into a elliptical configuration. Then spiral wrap and then foil tape. Attached some coax and then turned on my PI.
Air test depth wise, no different than the 7" round. What I did see, the detection pattern narrowed and lengthened.

Added note:The coil inductance was around 293uh when round, when bent
to shape it was 300uh. As you bend the coil, you can see the inductance go up on the meter.

Once I get the shells from Don, going to make an actual elliptical winding jig. Basically looking for an elliptical coil to get in between shrubs, rocks etc. when woods hunting...
Don mentioned the coil shell size would also make a nice DD coil for VLF's.

Welcome to the forum Bob.

[ATTACH]23317[/ATTACH]

Sven,

I have a round 12.5 inch coil that measures 310uH. When I squeeze it to being 6 inches wide the inductance drops to 280uH, about a 10 percent drop in inductance. Make sure you zero out the meter with just the test leads together before measuring the coil.

Let's see if others can try this simple experiment to verify my findings.

bbsailor

[SVEN1]

Hi,

OOPS my mistake the 7" coil orig. in round configuration was 314uh, when bent oval the inductance dropped to 300uh.
Just for the sake of it, squeezed that oval coil even more to a 2 1/2 x 9 and inductance dropped even further to 257uh.

I accidentally looked at the wrong tag that was attached to my other coil that started out round at 293 and thought that was the coils inductance.

[KahlesMilcon]

SVEN1,
Don't you need a opening in the foil so the faraday shield will work?
Just wondering?

[SVEN1]

If you look at the top of each coil you will see the black gap. This is the start and end of the shield.

[SVEN1]

Thanks to Don who made up some coil shells for me, I made up a jig to wind the 5x9 oval coil for my PI. Coil jig demensions were taken off the 7" round that I squeezed into an oval.
Wound up three coils and potted them into the shells. Preliminary bench tesing shows they have identical performance of the 7" round, just a narrow width search pattern that extends
the full length of the coil, similar to a DD VLF coil. An interesting note, it appears that it will still pinpoint just in front of the ears like the 7" coil.
Air testing I can squeeze out of the 5x9, 9-10" using my gold wedding band. Not too far off from the 9.5" coil pictured which gets 10-11".