Lets Talk F70 & F75 Coils

[Michigan Badger]

Let's Talk F70 & F75 Coils

I've had so many people tell me to get the F75 11" DD coil for my F70.

Now it's my understanding the stock F70 coil is concentric.

How can a DD coil be deeper than a concentric?

Maybe someone here with knowledge on these coils could set the record straight here for all of us because I'm sure many are wondering why the F75 coil makes the F70 so much better.

What exactly is the physical advantage of the 11" DD over the F70 stock concentric coil?

Thanks,

Badger

 

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[gmanlight]

Re: Let's Talk F70 & F75 Coils

MB I have the F75 with 11DD from what i have read some say + or - an inch on either coil
Depending who you talk to. I don't think it is enough to care The DD does well in mineralized soil
that i don't have and does well in trash that i do have. HAHA The 11 DD is nice but a little large
for the wood A new 5in round DD just came out. I have the 6.5 x 3.5 concentric so i will leave
the 5DD alone I would like something like a 9.5 x 4.5 DD that would be sweet
How much snow has to go so you can use that thing hh Mike

 

[Sky Pilot]

Re: Let's Talk F70 & F75 Coils

Badger, I wouldn't personally buy the coil for the '75 to replace the stock '70 coil, but as gmanlight said, you'll be waaay ahead of the game with the stock '70 coil and the 6.5x3.5 small coil! As a matter of fact, I usually use the large stock '70 coil on my '75, and keep the small oval on the '70 all the time. Believe it or not, (I know that coils are supposed to go "as deep" as they are in diameter), there is very little loss of depth with the small coil on my '70, although there is of course loss of coverage, when I use the 6.5, and the weight difference is an added bonus. I use them like this: F-75 with the F-70 coil to find an old homeplace, then switch to the F-70 with the 6.5 coil once I've located a promising site, then use the '70 or '75 with the 6.5 coil to snipe through the targets. Just my opinion and tactics, but hope it is helpful! Great hunting and good luck!! Regards, Richard.

 

[gleaner1]

Re: Let's Talk F70 & F75 Coils

My first reply to this didn't post, so I went to the Fisher site and confirmed that the F70 coil is a 10" concentric elliptical open center design. It can be argued that the F70 coil should be very close to the 11DD in depth because theoretically, concentrics are deeper size for size. Fisher now has 4 coils for the F series. I cant find anything for Fisher machines from EXcelerator. Not too long ago I saw an add in French for an EXcelerator butterfly for the F75. Does anyone know if EXcelerator makes coils for Fisher and where to find them?

 

[Michigan Badger]

Re: Let's Talk F70 & F75 Coils

Thanks guys this is a GREAT help.

One question more.

How many of you use the coil cover? I was wondering if you lose depth with it?

Badger

 

[George (MN)]

Re: Let's Talk F70 & F75 Coils

If the coil cover is, say, 1/16" thick, that might be the amount of depth you'd lose using it. That is of course a very small % of the power, considering the strong beep I got on a quarter in disc at 10" (air test). The only exception might be if some highly mineralized dirt were to get in there. You could probably guess that had happened if you had to start turning down the sensitivity or threshold more than before at a revisited site.

Also, the closer the coil is to the ground, the more likely to get surface & near surface overload from large coins. Some mfrs say sweep with coil 1" above ground, you can turn up the sensitivity higher in mineralized ground to make up for it. But if ground is low minerals, that might be an inch less depth.

Concentric vs DD: From what I've seen/heard, a concentric is deeper in the center of the coil, but a DD would be deeper nearer the edge & require less overlap. The DD might ID a coin better closer to the edge, as the concentric coil might get too weak of a signal for proper analysis.

I haven't paid much attention to differences in sounding off on junk, but thought I read DDs pick up bottlecaps more?? But I know with many detectors, a faster sweep speed will cause the bottlecap to break up.

What about the difference if any on concentric vs DD for picking up or not picking up electrical interference?

What if we use a concentric in high mineralization when DD would react less to ground minerals? What if we use a DD in an area with low mineralization? Are we missing coins? And what if the ground is highly variable? Would a DD be best in one spot & a concentric better 10 feet from there?

I guess all this shows it is hard to detect perfectly all the time. Maybe that's a good thing, or people would'nt still be finding old coins in parks & schoolyards that have been heavily detected for 30+ years. HH, George (MN)

 

[gleaner1]

Re: Let's Talk F70 & F75 Coils

George, good points, that's why I've always wanted more choices for the F machines. Now they have the 5" circular DD, the 11" elliptical DD, the 6.5 elliptical concentric and the 10" elliptical concentric. You need choices for the conditions.

I have the feeling the F machines with the 5" coil cannot be beat for picking up the very last goods in a really trashy environment. And I feel I would probably lean toward the 10 concentric in my less trashy spots just for the ease of pinpointing.

I really cant see an overwhelming advantage of the 11DD over the 10 concentric in friendly ground conditions, its just better seeing in between trash so you have to find out the trash density to decide between the two. I would start with the 10, then go back with the big DD in the trashy areas, working slower. Then the 5 in the spots you remember as being really bad.

I like concentrics because my conditions allow for it and I like digging the target in a small plug which is easy to do with a concentric. Its nice to have more choices as the conditions require.

 

[SaginawIan]

Re: Let's Talk F70 & F75 Coils

The 11" DD coil does great things for F70 . . . but I would probably pick up the 5" or 4x6" first - being that the 10" stock F70 kicks so much butt. Plus then you can be the small coil guinea pig and tell us all about it - so I don't waste my money!

I think the 10" coil is deeper but the 11" coil has MUCH larger footprint and better target separation with slightly less depth. The 11" DD seems to wrap the signal around trash to find things underneath. I think the 11" DD = more finds overall of the bunch. I have not noticed much target masking with it considering that one can switch positions and go at the target sideways and a little higher off the ground - and that 11" coil is really only 7.25 wide so it really is able to get in there pretty well

I was wondering about coverage per swing so I did some math.

11" DD = 11.5" x 7.25" = approx. 84 sq. inches
10" Conc = 10" x 5.5" = approx. 55 sq. inches
5" DD = 5" x 5" = approx 25 sq. inches
4x6" Conc = 3.5" x 6.5" = approx. 22.75 sq inches

So if you figure 1 swing per 1.5 seconds - covering a swath of about 6 feet per swing - over the course of a 1 hour hunt . . . um well, the 11" covers more . . .

Another thing, I don't believe a coil cover is necessary. I have about 120 hrs on mine over the roughest terrain ever - rocks, glass, sticks, and jean shredding thorn bushes. Not a scratch or nick. It is very very hard plastic - check it out I just took a picture of both sides. I wiped one side off and left the other like it was when I finished hunting earlier. Now my wife is going to kill me for getting mud all over the counter top,

Ian

 

[Charlie P. (NY)]

Re: Let's Talk F70 & F75 Coils

When you're considering field coverage remember the concentric "penetration" is conical - like an ice cream cone - under the coil. Not a cylinder. So, you may see a small target a foot deep, but the field path at that depth may be only 2" wide.

The DD field - with the area of greatest sensitivity being aligned along the fore-and-aft length of the coil - is more a "U" shape than a "V" shape in side-view cross section, so it covers equivalent or even more net depth on a single pass.

 

[George (MN)]

Re: Let's Talk F70 & F75 Coils

I have the 3 3/8" x 6 1/2" coil. I usually hate small coils, as I have too few areas where I need them & the stock coil is narrow, with DE mode giving good separation. My small coil correctly IDs a Franklin half at 10" in air test, SL all metal.

My list of places to use it: behind baseball backstops, along fences, near playground equipment, on the edges of parking lots & right next to picnic shelters, & maybe or maybe not along curbs & sidewalks.

For most of my areas, I think I'd prefer at least a 12" coil, as these park/school combos around here are mostly athletic fields, not much trash except moderate along the sidelines.

AFAIK, Kellyco is the sole US seller of the Detech Excelerator coils (made in Bulgaria?), so if that big butterfly coil becomes available it would be through Kellyco. Unless Fisher makes a bigger coil first. HH, George (MN)

 

[1491]

Re: Let's Talk F70 & F75 Coils

Thanks guys this is a GREAT help.

One question more.

How many of you use the coil cover? I was wondering if you lose depth with it?

Badger

I've had my F75 since May 2008, have used it in some rough places, and the bottom of the coil still seems brand new. Unless your hunting some extremely harsh substrate, you probably can go without a coil cover.

 

[gleaner1]

Re: Let's Talk F70 & F75 Coils

George I got the feeling the Bulgarians dont want any part of Fisher. I wonder why?

Badger I see you got your new machine and think the 10" coil looks small. I knew something looked funny about that thing! I wouldn't worry about it with all the good reviews, I'm seriously thinking about buying the F70 myself.

 

[Michigan Badger]

Re: Let's Talk F70 & F75 Coils

Another thing, I don't believe a coil cover is necessary. I have about 120 hrs on mine over the roughest terrain ever - rocks, glass, sticks, and jean shredding thorn bushes. Not a scratch or nick. It is very very hard plastic - check it out I just took a picture of both sides. I wiped one side off and left the other like it was when I finished hunting earlier. Now my wife is going to kill me for getting mud all over the counter top,

Ian

I missed this comment the first reading. Thanks Ian!

The coil cover is a pain and loves to trap dirt that really screws up a detector.

I'm glad one is not needed.

Badger

 

[Michigan Badger]

Re: Let's Talk F70 & F75 Coils

George I got the feeling the Bulgarians dont want any part of Fisher. I wonder why?

Badger I see you got your new machine and think the 10" coil looks small. I knew something looked funny about that thing! I wouldn't worry about it with all the good reviews, I'm seriously thinking about buying the F70 myself.

I really like my F70 so far.

One thing that seems to conflict with what Fisher claims is people keep saying the DD coil is better than the concentric coil in trashy areas. Fisher (1st Texas) claims the opposite.

The cone shaped signal of the concentric is better than the wide scan of the DD when it comes to a mixture of ferrous and nonferrous objects. The F70 detector has this in brief form printed right on the box.

Another statement that never really made sense to me is that the DD works better in higher mineral soil than the concentric. It's the same basic signal just a different pattern.

And too, the cone shaped signal of the concentric is somewhat exaggerated. Some people see this as a sharp upsidedown pyramid but really it's something between a V and U shape with jagged edges all around with a slightly deeper detection pattern at center.

The DD is fan shaped pattern (with jagged edges) with a slightly shallower detection pattern at center.

In some ways the DD is the opposite of the concentric.

The advantage in the DD signal is more ground coverage per swing but at the cost of some depth (side to side deflected signal). And too the DD coil at a trashy site location is at an disadvantage due trash masking.

The concentric coil's signal is not side to side deflected nearly as much as the DD signal and therefore goes much deeper but at the cost of less ground coverage per swing. But also the concentric is less affected by masking so therefore it's a much better coil for hunting the trashy sites.

The claim that the DD is better than the concentric at handling ground minerals to my knowledge has never been demonstrated as actual fact but rather is a subjective theory.

Badger

 

[thompy]

Re: Let's Talk F70 & F75 Coils

the DD coil is tough, been banging mine off the rocks in the U.P. around Marquette for 2 yrs and have one mark that i would call a scratch, my only issue is mine is it's not water proof

 

[JOE(USA)]

Re: Let's Talk F70 & F75 Coils

Any DD coil is less affected by ground mineralization than a concentric coil. Also the bigger the DD the less minerals it sees. So that's why it goes a bit deeper.The small DD coils have a sharper response to targets but require more difficult "compass direction" turning of the coil to defeat bridging. This is due to the front to back on edge rectangular detection field. The concentric coils have less bridging on deeper coins because of the funnel shaped detection field. It's really a matter of personal choice as to which one to use. Joe

 

[lost hunter]

I don't have a problem with caps My problem is with nails I think the F75 will pick up a carpet tack at a thousand yards lol

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[ozbach]

I hunt with a buddy that bought the 11" DD for his F-70 ....I tell you what he loves it, and I have seen, he is finding goodies left and right we have pretty crappy soil here, so I would guess it helped him out.