NEW COIL for the F75

This is a 6.5” elliptical concentric coil and will add versatility to the popular F75........

I was lucky enough to have a prototype of this coil sent to me. I gave it a really good workout over the last 2 weekends at some cellar holes (you may remember the flag tests posted here). I wanted to run some more tests early this week but it has poured the last 2 days.....But, after some tough tests, I'm about done, & here's what I have to report so far.....

My first impression was not that great, looks-wise, thinking it's just another heavy coil like the old Fisher ones. I have never been a big fan of small coils so I wasn't expecting a whole lot honestly. The white color didn't really "match" the look of the F75, but maybe when made they will be black....(But yes it's just a prototype & color is not as important as performance). I was also concerned at how this tiny coil was going to throw off the balance of the stock coil. I found out later in my opinion the F75 it's still balanced pretty good actually....I also got a prototype arm strap for the F75 but found I didn't need it with thsi new coil........

The good news is that once attached to the machine, I was pleasantly surprised at it's performance! An iron loaded cellar hole is a perfect place to test small coils (& if you saw the pictures on the forum, I used little flags to mark signals with both the F75 stock coil & the little one). I noticed right away that the small coil not only was great for separation, but it also added much additional stability. In other words, I ran sensitivity 77 with the big coil to mark targets & did so with some typical F75 background chatter. Then when the small coil was put on with the same settings it was so quiet I could crank the sensitivity up into the 90's (I settled on 93). Partially this is due to the smaller coil "seeing" less ground & iron I guess. But, this stability factor should be a real bonus to the folks who complain that the F75 is too "noisy" or like silent searching better. It may be good for salt water beaches, mineralized sites, or anyplace that people have said they are getting outside "interference" too (again this is an unexpected bonus I think). The depth was a big surprise as well as I have used small coils that separated but got like 1/2 the depth. This one, with sensitivity boosted up, hit on every target the bigger coil did except 2. Interestingly the 2 turned out to be iron so I'm thinking it perhaps ID'ed better & got better separation in those cases. It's a small coil, but not "too small" that you feel like you covering nothing. Like I have an old round Fisher 3.5" "sniper" coil that seems a bit too small. This one being elliptical is a good way to go I think. I think it's going to really do well in trashy sites, & I think this will really satisfy the masses cry for smaller coils. Like I mentioned, I have never liked small coils personally, but I can see a definite place for this in the cellar holes I do. I will keep one in my backpack at all times.....

Finally, It's size/shape also allowed me to stick it down into some open holes to see it the target was deeper or in the side wall. I found 2 items in the sidewalls this way....So, there's mostly all positives for me at this point, & I'm hearing First Texas will get rolling on getting them out ASAP as the other fields testers experienced similar results...... I expect it to be a great tool for trashy hunting.
More later........
Here's a photo of the coil showing the big difference in size........
HH,
Bill

Thanks Lawrenzo for the re-post. Yes, I'm sure it's the Gold Bug I/II coil housing. This would make perfect corporate financial ( & tooling ) sense. The question is: Compared to the standard 7-11 coil....What is the ratio of depth LOST VS enhanced adjacent target separation GAINED. It's usually not a linear differential. If it's not a true 'DD'.... then the enhanced adjacent target separation gained will lessen the ratio.

Tom

How about ultimate sensitivity to small low conductive targets at depth? Small elliptical concentrics in decent ground are hard to beat sensitivity wise!

I see quite a few relic and coin hunters asking for a large concentric coil for the F-75. Theres a lot left out there to find in open ground too.

Tom



Edited 1 time(s). Last edit at 09/19/2007 11:05AM by Jackpine.

The F-75 is already quite sensitive to low (foil range) conductive targets……. and a smaller coil , with near certainty, should boost this level a bit more.

I am a STRONG proponent of a larger concentric coil (say 10.5”) for the F-75. This would most probably prompt me to never hunt inland again with a CZ….. As it would most likely match the CZ’s depth capabilities on coin-sized (and smaller) objects,,,,,, especially the lower conductors ((( although I am after the higher conductance coins ))). As it stands right now…. A large coil equipped CZ (in my neck-of-the-woods) is still the trump-card. This is to say that; every time I perform a inland hunt,,,,, I always have a 10.5” CZ AND a F-75. Would be nice to have only one.

Tom

Sensitivity to foil range targets will be very good ofcourse but can there ever be a too sensitive coil made. The small F 75 coil is a cc, I wonder why they did not make it a DD. I think it would distribute the sensitivity better in the ground not making it so sensitive to minerals and silent masking.

The new x-terra 6" DD is capable of finding nickels at 8" and small wads of foil at 6" in some trash and it is completely stable. It have to be experienced to be believed, i understand that.However it is true. I dont think the same coil as a cc would do as good.

""TOO Sensitive of a coil"" is interpretive...... BUT... in general,,,, and to still answer your question = A coil is only part of the equation in sensitivity gain. Most of 'sensitivity' is taking place in the electronics.... and not the coil. A coil DOES make a difference..... but, yet... most is determined by the gain of the control box electronics.

And yes, if the coil is not a DD, than it is more susceptable to mineralization interference and masking problems. There may be perceived concern that TOO MUCH depth is lost by making the smaller coil a DD also. I do hope that it is a true DD..... and sure,,,,, there will be a loss in depth BUT.. there should be a tremendous gain in adjacent target separation properties. And is that not just exactly why you would install a smaller coil on your detector?

Time will tell all.


Tom

NASA-Tom Wrote:
-------------------------------------------------------
>
> And yes, if the coil is not a DD, than it is
> more susceptable to mineralization interference
> and masking problems.
> I do hope that it is a
> true DD
> And is that
> not just exactly why you would install a smaller
> coil on your detector?
>
> Time will tell all.
>
>
> Tom


Tom, You got my point " and you added some science to it "

But the new F 75 coil is a concentric.

Why,,,,,, I think it will still mask and due to the sensitivity of the machine meet more struggle from the ground then with a DD, My personal experience with many makes and coils is that this Machine would do just great or even better with a DD, see my Terra experience in my last post. The small 6" concentric at 7.5khz for the terra is not up to the performance of the 6" DD at 18.75 even et higher conductivity targets.

Strange but true.

Maybe its got something to do with Minelabs proprietary chip in the coil and it adjusts the gain from communication with the coil.

Its a question still to be answered.

DD coils can make a detector a completely different animal. Yes, lower operating freq's make a detector more sensitive to silver/copper..... and higher freq's are better suited (resonant) to lower conductors like foil/gold.......... but, yet.. a DD coil on a high-freq unit may find silver/copper coins better than it's counterpart equipped with a concentric coil at a lower freq...... especially if large amounts of iron are present. Single freq units are better in iron.... multifreq units are better in bad ground. It's all in the variables.... and there are a ton of variables out there.... giving us 'selection' to better suit our specific application.

Tom