Here is what I know and I hope covers the common questions.
Optimized (White) 10x12 SEF Coil
SEF stands for (Symmetric Electromagnetic Field). The SEF coil is a modified DD or OO type coil where the two loops overlap each other in the middle. When testing the prototype V3i I experienced less ground noise, slightly better depth and better coverage with the non V rated 12X10 SEF coil that I was using at the time. The canceled ground noise is probably what allows you to hear deeper targets better. The 10X12 is two inches longer than the D2 coil which gives more coverage per swing. They are made in Bulgaria and Kellyco is the only place you can get them in the USA.
The original black coils had some drawbacks and were not optimized for the V3i and VX3. My old (black) SEF, which was suitable for Whites DFX, MXT and M6, did not allow me to get the best efficiency with my Spectra. This was due to the nulling which is not optimized for the 3 frequencies the Spectra uses. It was possible to use the old SEF with a single frequency 2.5 kHz or 7.5 kHz but in multi-frequency and single frequency 22.5 kHz I had to decrease the sensibility considerably. The use of Boost Mode was out of the question. The black coil always overloaded. Many of the coils would be limited to RX 9. Also, the VDI numbers were off on low conductive targets. A nickel would read as a 25 VDI rather than the usual VDI 19.
The white-colored Detech SEF coil is optimized, no V rated, for use with the V3i and VX3. Of course the first thing I noticed was its white color. The white colored coil does not absorb ultra-violet rays as much as black colored coils and subsequently the coil runs at a lower temperature. This reduces the internal coils induction balance drifts which are caused by exposure to direct sunlight. This gives a better stability to the metal detector.
My white 10x12 SEF weighted less than my D2. The coil is center mounted so it has excellent balance. Here are the two coils, my D2 and 10x12. Both have no cover and have the lower shaft attached. My white 10x12 is lighter.
[attachment 254704 2013-01-16_133912.jpg]
The white SEF I have solved the null problem and allows high RX settings. My White 10x12 is a good one but still does not have as good a null as my V rated coils. The white SEF doesn't run as low a signal% as my D2 but it is not that much higher. My SEF however will not overload at RX15 with boost on.
[attachment 254705 2013-01-16_134203.jpg] [attachment 254706 2013-01-16_134223.jpg]
Some non V rated Whites coils and black SEF coils, by luck, can run boost. I have my doubts about the White SEF manufacturing tolerances and don
Optimized (White) 10x12 SEF Coil
SEF stands for (Symmetric Electromagnetic Field). The SEF coil is a modified DD or OO type coil where the two loops overlap each other in the middle. When testing the prototype V3i I experienced less ground noise, slightly better depth and better coverage with the non V rated 12X10 SEF coil that I was using at the time. The canceled ground noise is probably what allows you to hear deeper targets better. The 10X12 is two inches longer than the D2 coil which gives more coverage per swing. They are made in Bulgaria and Kellyco is the only place you can get them in the USA.
The original black coils had some drawbacks and were not optimized for the V3i and VX3. My old (black) SEF, which was suitable for Whites DFX, MXT and M6, did not allow me to get the best efficiency with my Spectra. This was due to the nulling which is not optimized for the 3 frequencies the Spectra uses. It was possible to use the old SEF with a single frequency 2.5 kHz or 7.5 kHz but in multi-frequency and single frequency 22.5 kHz I had to decrease the sensibility considerably. The use of Boost Mode was out of the question. The black coil always overloaded. Many of the coils would be limited to RX 9. Also, the VDI numbers were off on low conductive targets. A nickel would read as a 25 VDI rather than the usual VDI 19.
The white-colored Detech SEF coil is optimized, no V rated, for use with the V3i and VX3. Of course the first thing I noticed was its white color. The white colored coil does not absorb ultra-violet rays as much as black colored coils and subsequently the coil runs at a lower temperature. This reduces the internal coils induction balance drifts which are caused by exposure to direct sunlight. This gives a better stability to the metal detector.
My white 10x12 SEF weighted less than my D2. The coil is center mounted so it has excellent balance. Here are the two coils, my D2 and 10x12. Both have no cover and have the lower shaft attached. My white 10x12 is lighter.
[attachment 254704 2013-01-16_133912.jpg]
The white SEF I have solved the null problem and allows high RX settings. My White 10x12 is a good one but still does not have as good a null as my V rated coils. The white SEF doesn't run as low a signal% as my D2 but it is not that much higher. My SEF however will not overload at RX15 with boost on.
[attachment 254705 2013-01-16_134203.jpg] [attachment 254706 2013-01-16_134223.jpg]
Some non V rated Whites coils and black SEF coils, by luck, can run boost. I have my doubts about the White SEF manufacturing tolerances and don