Wow I can't believe I got out yesterday to dig. It seems like work and the stress of things in 2020 took a toll on my detecting experiences for quite a while. I wanted a new coil for the MK and saw a post Kac made about the Nel Superfly, So I said what the heck I'll give it a try. This coil is 6 grams lighter than my 9 inch. I must say this coil is amazing!!! great depth and way better separation. So I went to give it a spin on a site I hunt that has some modern and 18th century history to it. (ball fields and farm fields). I swung for about 5 hours in the 35 degree weather, and found a bunch of coins,(1941 penny, 46 nickle) shot shells, suspender clip, fishing reel, and a fragmented old bell. I wish the bell was whole, because it was about 2'' in dia. The reel perplexes me because of the lack of water in the middle of a 20 acre field. Overall I had a really nice trip out, I was starting to forget how detecting can clear your mind.
PS Joe D can you please send some of the Florida warmth up here to PA.
By James Ryan
I've always wrapped the coil wire around the shaft a few inches up from the coil. But then I saw in a some people mentioning they run the wire straight up the lower shaft then start coiling the wire above that. Someone mentioned the reason he does this is because of the magnetic field and possible interference wrapping it shortly above the coil. I have only been detecting about 7 years and always trying to learn more. Any advise/suggestions ect. on this would be great and thanks in advance.
Hi Folks, I'm developing a new VLF analog prototype detector and am using a concentric coil I've seen in the book "Inside the Metal Detector", it has the TX coil in the center with upper and lower RX coils that are balanced. So I have some questions for you experienced folks: Does anyone know if this style of coil is still used? If not, does anyone know why it fell out of favor? Any pro's and con's? Thanks for your help, I'm considering showing some of the pic's as I progress, I have the next revision pcb on order, we'll see how it goes.
I did some testing in my back yard to compare relative depths achievable in my soils with various coils on the Fisher F75.
Caution: these are relative measurements specific to my soil conditions (including ferromagnetic mineral content and current moisture content). The purpose is merely to compare coil sensitivity for particular settings which push the detection depth limit under these conditions but otherwise should not be used as an absolute indication of how this detector with these coils mounted will perform under different conditions by other detectorists. My ground is of moderate mineralization, measuring 2-3 bars on the F75 depending upon exact location in my backyard and coil choice (higher reading for largest coils).
Detector setup: Fisher F75 Limited (black) operating in motion 'all metal' (USA nomenclature, not Minelab's!), DST on, gain=99 (max), ground balanced, noise cancelled, threshold=0. I plugged Garrett GS2 headphones directly into the socket, i.e. 'wired' headphones.
Test targets: 5" deep 95% copper Memorial USA 1 cent, 6" deep 25% nickel, 75% copper USA 5 cent ('nickel'). (These have been in the ground ~ 2 years.)
Measurement meaning: because the coins are at fixed depth, in each measurement I raise the coil until I lose the signal in either left or right swing directions. That is, I require the target to sound off clearly as the coil moves from left to right and from right to left. I use wood blocks as shims with a least significant thickness increment of 1/2" (~1.3 cm). I estimate half that or 1/4" as the measurement's systematic uncertainty. Note that these measurements are intermediate ('hybrid') between full ground and an (full) air test.
Fisher stock 7"x11" DD and 5" round DD (both included in the Limited/black model package), Coiltek 6" round DD prototype (built for Fisher F5 and operated successfully on my Fisher Gold Bug Pro), Mars 6"x10" DD Sniper, and Detech 13" round DD Ultimate. (I forgot to test the only concentric I have for this detector -- Fisher 5.5"x10" which is the stock coil on their F70. I'll do that later this week and add it to the table below.)
Summary/Conclusions: With the exception of the yellow-highlighted Coiltek prototype (which was not designed for the F75), the order of depth does reflect coil size. The Mars 6"x10" DD performs almost as well as the stock Fisher 7"x11" DD. The largest coil, the Detech Ultimate, is only a bit better than those two which likely reflects the considerable increase in ground it 'sees'.