PI, Oval Coil

[chemelec]

My latest attempt to make a Flat Radial wound Oval Coil.
Size is 7" X 9 1/2" OD, wound with 22 AWG wire.
Inductance 397 uH.
Turned out Good, Now to test it.

[WM6]

My latest attempt to make a Flat Radial wound Oval Coil.
Size is 7" X 9 1/2" OD, wound with 22 AWG wire.
Inductance 397 uH.
Turned out Good, Now to test it.

Nice looking, awaiting on test report.

[silverdog]

Flat Oval Coil

My latest attempt to make a Flat Radial wound Oval Coil.
Size is 7" X 9 1/2" OD, wound with 22 AWG wire.
Inductance 397 uH.
Turned out Good, Now to test it.

That is a piece of Art

[WM6]

35 turns according my eye-calculator.

[chemelec]

35 turns according my eye-calculator.

Actually its 42 Turns.

[Carl-NC]

Very nice work Gary, as usual!

[chemelec]

Very nice work Gary, as usual!

Well as much as it Looks Nice, It doesn't actually detect any better than my 8" Round Coil. (My Gold Ring at about 12 Inches and Quarters at 10 to 12", depending on metal content.)

I was actually wanting to make a coil about 4" X 10" , but I can't do that Narrow of size with my present Jig. (Without Probably Screwing it Up.)
So maybe later I'll get some more 1/2" Lexan to make another Jig, Just to wind these Narrow/Long Oval shapes.

Aways Expermenting!

[mikebg]

It doesn't actually detect any better than my 8" Round Coil.

Aways Expermenting!

Gary, I think the oval flat spiral coil must have three advantages:
1. Wider scan, which depends on the large external diameter D_ext (as scan direction shown below);
2. Better pinpointing, which depends on the small internal diameter d_int;
3. Better sensitivity to very small objects, which depends on the small internal diameter d_int.
However more important is what Aziz thinks

[chemelec]

Gary, I think the oval flat spiral coil must have three advantages:
1. Wider scan, which depends on the large external diameter D_ext (as scan direction shown below);
2. Better pinpointing, which depends on the small internal diameter d_int;
3. Better sensitivity to very small objects, which depends on the small internal diameter d_int.
However more important is what Aziz thinks

I Agree, That is Why I previously said I really wanted to make a coil of about 4" by 10" OD.

(Small Width to better detect Small Objects, But long Length to detect a Wider Area and bigger objects also.)

My Present Jigs do a Good Job in making very nice coils, But These Oval Coils need a Different overall shape and Layout than what I use for my Round Flat Coils.

Gary

[gef12]

Hi Gary
Nice coil and thanks for sharing ..
what would be the impedance be ?

[chemelec]

Hi Gary
Nice coil and thanks for sharing ..
what would be the impedance be ?

Presently, DC Resistance is 1.08 Ohms to Ends of 8" Lead wires.
Q = 2.15 @ 1Khz

[Bob_T]

I'm new here and I'm getting started on building a PI detector and winding my own coil. I wondered about any advantages of oval coils and although I'm sure there are more threads here, this is the only one I found that addressed oval coil building. The advantages listed here seem to make sense on paper but I'm wondering about any practical compromises or disadvantages when compared to a conventional round coil? There must be a reason why the majority of coils are round, other than being simpler to build?

Thanks,

Bob

[dfbowers]

Oval coils.

The right tool for the right job I suppose. They are the thing to use for tight space (woods and between corn stubble).
Sven had me vacuum a few shells for him lately so I'm curious to see how his projects work out.

[SVEN1]

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.

[joop]

Presently, DC Resistance is 1.08 Ohms to Ends of 8" Lead wires.
Q = 2.15 @ 1Khz

Did you measure parasitic capacitance? I expect it to be very low, maybe 50 pF...