what does sef stand

[rewmarshall]

i was just wondering what the diffrence was between a dd coil or a concentric coil vs a sef

 

[Larry (IL)]

S.E.F. Symmetric Electro-Magnetic Field

It is all in how the coils are wound. Someone will have graphics, I can't find the ones I saved. The concentric coils are usually round and sometimes slightly elliptical and have a conical (cone shaped) detection pattern. The DD and SEF coils have two windings side by side if you would turn around the first D in DD so the flat part of the D's are back to back might give you an idea. The SEF coils are DD but slightly overlap each other and DD/SEF coils radiate a windshield wiper type pattern into the ground roughly an inch wide the length of the coil.

 

[earthmansurfer]

Thanks for that description Larry. I actually was wondering a bit of the same.

I did a search and here is an interesting post from a mod on another forum. I'm posting it because an SEF coil seems like the perfect coil in my mild but iron filled ground. Note the bolded and sorry but there were no graphics on the site:

I only have one SEF Coil (12x15), but here's my view of the differences from a hunting (not electronic) viewpoint. My "artwork" is hardly the best, so bear with me please. :

As depicted in the drawing below, the shape of the Transmit and Receive coils are "D-shaped", placed back-to-back. The narrow "detection area" (my term) is indicated in RED. The narrow area allows for excellent target separation and provides the maximum minimization of the effects of ground minerals. However, the detection area (square inches) is considerably diminished.

The SEF coil has the oval Tx and Rx coils overlapped to create a wider detection area...shown in RED.

The SEF is (IMHO) a compromise between a traditional concentric coil (CC) and a DD. It offers better separation of targets than a CC, but not as good as a similar sized DD. The SEF is much less prone to the negative effects of ground minerals than a CC, but can't equal a DD in that area.

So, why even bother with an SEF coil? The answer is (IMHO) a larger detection "footprint" which results in increased depth when compared to a comparably-sized DD coil.

My limited SEF experience shows that the SEF is superior (depth-wise) to the DD in light-to-moderate ground mineral conditions. However, in areas of high mineralization...the SEF does not perform as well as the DD when seeking deep targets.

I know Cybersage has done a lot of good work with both SEF and DD coils in his test garden. Perhaps, he can offer some more insight than my overly simple viewpoint.

Hope this helps.

 

[rewmarshall]

thanks that explains alot

 

[Larry (IL)]

"The SEF is (IMHO) a compromise between a traditional concentric coil (CC) and a DD. It offers better separation of targets than a CC, but not as good as a similar sized DD. The SEF is much less prone to the negative effects of ground minerals than a CC, but can't equal a DD in that area."



I couldn't disagree more with his opinion on the negative ground affects of the SEF. My experience (in my ground), the 10X12 SEF had better ground noise reduction than the D2 and EX10" DD when I was testing coil compatibility with the prototype V3. I reported my findings to White's and the Engineering Dept. had similar results in the lab. I also disagree with his depth assumption and I believe the SEF is not only quieter but deeper than a DD the more mineralized the ground is due to the SEF is quieter and I can hear the whisper of a deep target that would be masked with ground noise with a DD coil. Again, this is just my opinion in my ground and I'm not trying to sell anyone's coils but I use the 10X12 SEF on both the V3i and Minelab SE for good reason.......... they work better for me.