I have had a Garrett ACE 250 for several years and just bought a very slightly used Garrett AT Pro a week ago. A couple of times I did not get any sound when first turned on but after wiggling the coil cable it started giving tones again. On occasion it has suddenly started chattering with almost no movement and I have done a reset and it corrected the problem. My main issue right now is that if I bump the coil cable close to the connector I get a tone every time. I have removed and re-inserted the connector twice making sure it is fully inserted but still get the tones. I have made sure its not the connector itself. I don't have another coil for the AT Pro to swap out. I texted the previous owner to find out when he purchased it hoping it was less than the 24 month warranty that Garrett has. Wondering how strict Garrett is on fixing issues like this or replacing a coil with a bad cable if I was not the original purchaser. Any suggestions are appreciated.
By Steve Herschbach
This is not about detector versus detector. It is just a video questioning if small coils are always better in trash, and whether concentrics are always better than DD coils at handling ferrous targets. Too bad about the wind noise. Good stuff though illustrating there are no magic answers.
For detailed information see this article VLF Concentric Vs DD Coils
By Steve Herschbach
VLF detectors can come with DD or concentric coils. This is similar to but not quite the same thing as DD versus mono on a pulse induction detector. There are three basic coil types in wide use, Concentric, Double D (DD) and Mono. A VLY detector transmits and receives simultaneously and so there must be both a transmit coil and a receive coil. A pulse induction (PI) detector can alternate between transmit and receive and so one coil can be employed as both transmit and receive in an alternating fashion. There is confusion on this but simply put VLF (induction balance or continuous wave) detectors do not employ mono coils. A VLF can only employ the concentric or DD options. A pulse induction coil can work with all three types.
Metal detector coil types illustrated - concentric vs DD vs mono
VLF detectors are more alike than different these days. One thing that can make a real difference is what coil the detector comes with. Two very similar models will be quite different if one comes with a 12" round concentric, and another an 11" x 7" DD.
In this case the very same detector can be turned into two different detectors by changing coils. Here are a couple rarely seen on the F75 - the 10" x 5" DD and 10" elliptical concentric. A big difference between the Teknetics T2 and Fisher F75 was that the F75 came later and the ability to use concentric coils was added. The T2 can only use DD coils.
Why DD or concentric? DD coils are all the rage these days. However, concentrics have more consistent detection patterns with less dead spots up close. Every notice how that DD coil goes wacky on shallow targets? And concentric coils are much better at identifying flat ferrous targets like bottle caps. Here it is from the guy that should know best, Dave Johnson, lead designer on the F75.
About Search Coils by Dave Johnson
Search Coil Field Shape by Dave Johnson
Coil Basics by Carl Moreland
I like the 10" DD for the solid design, better for working in stubble or other locations where an open coil might hang up. The concentric just for being better behaved. The DD is the better prospecting coil for bad ground. Concentrics do well on milder ground.
A note on coils. The blade like knife edged detecting pattern depicted in DD marketing ads is largely myth. Electromagnetic fields radiate and simple coils cannot focus them into beams. A round concentric coil has a search field shaped like a soccer ball cut in half. A similar size DD coil will have a search field more like a football cut in half lengthwise. If you ever doubt this, just fire up your detector with a DD coil, flip it over, and run a coin under the coil noting where the signal fades at different locations under the coil.
Finally, depth is more related to coil width than coil length. Think of a 5" x 10" coil as a stretched out 5" coil, not as a skinny 10" coil. That is why when listing elliptical coil sizes you will often see me putting the small number first. Marketers do it the other way around so you tend to think you are getting more than you are.
Fisher F75 with 10" Elliptical DD Coil
Fisher F75 with 10" Elliptical Concentric Coil
Dilek has mentioned this on some of the forums that a new coil offering for Impact much like what is given on Anfibio package. Looks like the coil is indeed loaded to Nokta’s site now.
There are a couple lots on Ebay where the seller includes a Tesoro Widescan (DD) 5 3/4 inch coil with plug modified/replaced to operate on a Fisher Gold Bug (the new generation Gold Bug, not the 1990's versions). I'm wondering if anyone here has heard about the possibility of going the other direction -- putting a Fisher Gold Bug / F19 / Tek G2,G2+, Tek Greek series coil on a Tesoro?