Fisher 10.5" Elliptical Coil - How does it differ from a Concentric or DD ?

[Cal_Cobra]

Can someone please explain how the Fisher 10.5" elliptical coil differs from a concentric or DD coil (the one they use on the Coinstrike, CZ, etc) ?

What advantages or disadvantages does it have over the others ? What's an ideal hunting situation for it ?

Thanks!
Brian

 

[Charlie P. (NY)]

The "dead flounder" coil of the F-75 is a Double D. It's equivalent to a round DD of the same (largest) dimension. Excellent in trash as it "paints" a long but narrow field. Better in mineralized soil (no accident the Minelabs use DoubleD for Australian soil), more work/time to pinpoint accurately with (requires turning it 90

 

[Cal_Cobra]

Charlie thanks, that makes sense, I think I have a decent understanding of the DD coil. MY Fisher F4 uses the same DD coil as the F75, and so far I think it's a good coil, covers a lot of ground quickly that's for sure.

I'm not sure about the Fisher 10.5" elliptical coil which is a different animal.

Thanks,
Brian

 

[Charlie P. (NY)]

Ahhhh. I gotcha. We're talking a coil like the Gold Bug 2 - an elliptical co-planar?

I believe they would behave like a fully round concentric but have a slightly reduced depth (comparing the largest "diameter" of the elliptical to the circular coil). The advantage would be light weight and easier to poke around with than a round coil of 10-1/2".

Not sure on that.

 

[Cal_Cobra]

It's this one:

I was just searching on the concept of Elliptical / Elipse and found that mathematically it's a very interesting coil, a slanted cone shape if you will.

If that's how this coil operates, it would seem logical that the pinpointing wouldn't be in the center of the coil, but rather where the center of the cone field slants, such as the blue line in the second photo below. Question is which end of the coil is the tip of the cone, the heal or toe ?

 

[Charlie P. (NY)]

That's the Fisher "Spider Coil". It's a concentric in practice. I think the center elliptical loop transmits & outer circular coil receives. So, while the field is distorted it still is received by a circular antenna and the nexus is still the center.

 

[Cal_Cobra]

Thanks Charlie, that's good info. I'm thinking they must have had a reason to make it a concentric receive with an elliptical transmit.

Is the advantage a tighter search field vs. a "normal" concentric search coil ? Or is it a deeper reaching search field ?

I'm thinking about trying this coil out at the beach this weekend.

 

[Jackpine Savage]

Actually the center ellipse is the receive coil. the shape is unique for sure and has its advantages. The first CZ-5 I had came with that coil and I used it exclusively for many months before getting the 8"'er. Its not that hard to work with if you hip mount the control box and I could hunt all day with it despite the weight.

The main advantage in my opinion is that since the field shape of a coil is actually dependent on the targets under the coil at any given time (as opposed to the generally accepted notion of a transmitted field being blade shaped for a DD or cone/bowel shaped for a concentric) this design gives the coil a unique look at co-located targets and coins "on-edge" that other coils may miss. Whether you hunt with a concentric, a DD, or this one they should all find targets the others miss.

Just another tool for the arsenal and a darn good one at that.

tom

 

[Cal_Cobra]

So the advantage over say the 8" Fisher concentric isn't so much for depth, but more so a different search field position. If I have it correctly, then the last image I posted showing the blue line as the search field would really explain why it would be great for coins on edge.

Thanks,
Brian

 

[BuckeyeBrad]

Is that bowel shaped or bowl shaped? Another example where that limited time edit feature isn't cutting it.

 

[Jackpine Savage]

Boy am I ever :blush: I read that line twice before posting and knew something was wrong with it!

 

[Cal_Cobra]

bowels and DD's , my oh my, I think I'm on the wrong forum

 

[Charlie P. (NY)]

Whadda-I-know? I get most of my theory information from a 1985 edition of Charlie Garrett's "Modern Metal Detectors" and, for reasons unknown, he never even mentions Gerhard Fisher's inventions, the "M-Scope" days, later contributions and detecting accomplishments and entirely skips Fisher's later coil designs, the spider coil included. Go figure??

 

[vlad]

Its an early design, they made elliptical concentric coils for TR's back in the early '70s. I believe the reasoning was to try to stretch out the hot spot in the center and allow you to cover more ground. This was before George Paine came up with the motion design, and many manufacturers made straight VLF's, or TR's and had not combined both in one detector. I wouldn't be surprised if you could find some old photos of early models with this type of loop. [This was at a time when BFO's were considered the most
popular detector.]