Why do some think the F70 coil is better than f75 coil

[p2c]

Hi all,
I've had my F-70 since March and have just gotten the 11 " DD this week. I've read posts where people claim that the 10" concentric (F70) is deeper in non-mineralized soil. I have only had the 11 DD (F75 coil) for 2 days. Not much experience with it yet. But with air test it is far superior, getting at least 2.5 more inches. I can't imagine it would be deeper in low FE soil or in any other soil (given its better in air distance and that all claim it handles bad soil better). The only situation I could see use for it is if you need a slightly smaller coil to get into places.

I only ask, because I am trying to figure out if or when I'd ever use the F70 coil over the F75. Sort of a detecting strategy question (or even deciding to keep the 10" coil).

Thanks
-Jon

 

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[George (MN)]

I think the deepest coin I've found with the F70 w/DD coil at the park/school combo nearby is a dime at 4". With the concentric got a dime down 5" & a penny down 5 1/4" + 2 or 3 more pennies at 4".

It's hard to get good depth & accurate ID at depth in my ground.

Most of my ground is not showing on the ferrous indicator but it has little pockets of iron every few feet & hot rocks popping with or without a high number displayed.

I'm only part way through my DD air tests but sometimes the concentric does a little better, sometimes the DD a little better, sometimes no difference.

Of course air tests are with the detector ground balance stuck on 90. In my actual ground, the balance is from upper 50s to lower 70s. Once I accidentally did something (not sure how) that made GB lower in my air tests and it responded better to coins out a foot or so.

I think if the DD coil is run with too high threshold or sensitivity, some trash like bottlecaps breaks through. I don't notice that so much with the concentric, using the same settings. The DD obviously has better separation side-to-side, while providing somewhat better ground coverage.

I'm waiting for some rain to plant coins for comparison tests. HH, George (MN)

 

[p2c]

I think the deepest coin I've found with the F70 w/DD coil at the park/school combo nearby is a dime at 4". With the concentric got a dime down 5" & a penny down 5 1/4" + 2 or 3 more pennies at 4".

It's hard to get good depth & accurate ID at depth in my ground.

What sort of settings are you using? Autotune or disc? If in disc, I've found best depth in such places at disc = 0; although disc=6 supposedly gives better iron unmasking with the DD coil. Curious that you are finding better depth with the concentric. That is not my experience so far. I think Tom Dankowski states somewhere that the F75 coil usually gives about 1.5" over the F70 coil. What sort of soil do you predominately have? (red clay, brown clay, non-clay?)

 

[Streak!]

a few things to consider......

With all due respect to everyone’s opinion, it’s hard to compare "depth" without setting a few constants.
Is the depth better on one coil better because of the type of conductor?? (The F75 and F70 will tend to excel on lower conductors) Are GB settings the same and "fixed" ?
Are you using the same modes? What kind of dirt is it?
Concentrics are almost always deeper, everything else being equal. The 10" elliptical concentric and 11" open frame bi-Axial DD are no exception.
One thing I see all the time is the statement.... "When I start detecting in the air, I'll believe in air-tests". That’s one of the dumbest statements I've ever heard. Most all folks...AND.....manufacturers included use air-tests for a benchmark. Air-tests aren’t much use on pulse machines, but are a good indicator of overall performance on VLF machines. Also, anyone that has ever detected on white sand beaches, certain kinds of soils, in walls or in stone walls has detected "in air", so air tests DO have a bit of relevance.
While concentrics DO usually get better depth in common soils, DD coils will usually trump them on depth in "hot" soils, or soils with a high FE content, because they can "see" better in those types of soils.
On my F70 and F75, the concentric does indeed get better depth on most conductors, but by a shallow margin. The exception to this is the F70 in SL mode. In SL mode with the concentric...the F70 is deep as heck.
I guess I ought to define "deep" too. When I think about depth, I think about EFFECTIVE depth. That is........ not so much whether I can "see" the target, but whether or not I can “see” it good enough to want to actually DIG it! THAT is a BIG distinction!
When you DO do air-tests......and compare machines and coils, I’d do a reset on either machine (I’m talking about the F70 and F75 here), so that the sensitivity settings, modes and GB are at default. THEN and only then do your air-tests. If you had a piece of Ferrite you could GB to that as well, but the end result would probably be the same.
Also, when you do the tests, try to use the same vector and distance when sweeping the target. A slight change in orientation can change the results big time on certain types of targets. Do you tests OUTSIDE the house away from any possible RF interference sources.....and make sure your hands and wrists are free of watches......rings...and jewelry.
I actually saw a guy trying to do air-tests while holding the shaft just above the coil with a big old honking watch on.......and wondering WHY he couldn’t get any depth.
The short answer is...................that I think BOTH coils are valuable and useful, and I wouldn’t be without either of them. (Besides......if you sell the stock coil off the F70...and ever want to sell the MACHINE ......you’ll be minus the coil that came with it) Now..........having said THAT, I STILL use the 11” DD 90% of the time on both machines. Some guys will tell you that DEPTH is supreme............but where I hunt...................SEPARATION is supreme. The truth is.....most targets aren’t all that deep on MOST sites........................BUT.....................BUT................masking IS a big problem, and the coil that handles masking best is the coil that’s likely to put the most goodies in your pouch. I’ll use the concentric on big open sites where targets are deep and sparse...........but on every other site its the 11” coil all the way....on BOTH machines.
I’d keep BOTH coils........as your likely to find a use for BOTH........depending on where you hunt and soil conditions. Another little gen you may want to consider is the little 5” DD coil. Next to the 11” , the 5” coil is the coil I use the most. I haven’t found much use for the little concentric......but I LOVE the 5” DD!!!
Hope this helps a bit................ Streak!

 

[Streak!]

What sort of settings are you using? Autotune or disc? If in disc, I've found best depth in such places at disc = 0; although disc=6 supposedly gives better iron unmasking with the DD coil. Curious that you are finding better depth with the concentric. That is not my experience so far. I think Tom Dankowski states somewhere that the F75 coil usually gives about 1.5" over the F70 coil. What sort of soil do you predominately have? (red clay, brown clay, non-clay?)

I dont know WHERE you read that a disc setting of 6 gives better unmasking than a disc setting of "0", but it isnt correct. I've demonstrated many many times where a disc of "0" will allow you to detect a target....... where at a disc setting of "6" the target is completely invisible!
I have a site across the road I call the "Reservation", that has produced a ton of early indian cents (among other coins). After getting as many targets as I could at a disc setting of "6", I went down and changed to a disc setting of "0". When I'd get a diggible target at "0", and switch back to "6", and on a full 80% of the targets the target would be gone! Oddly enough, at a disc setting of "0", you could not only hear the targets, but they would ID correctly as well. Switch back to "0" and they would be completely gone! Respectfully, Streak!

 

[limegoldconvertible68]

My biggest problem is old, deep iron. My F-70 loves the stuff. I usually run with the disc at "6" but many nails give a very good audible signal. Then I repeated sweep the target as instructed in the manual and get ID's ranging from "67" with four confidence bars up to "83" with 2 or three confidence bars. After digging hundreds and I do mean hundreds of nails I now circle the target in 2F mode and if at any certain direction the target will no longer give a solid signal but instead give the low iron buzz I don't dig it. How do you make certain there is or isn't a good masked target present? Is this just a case where the stock concentric coil is the wrong coil to use? Is this a common problem and does the 11" DD greatly improve this situation?

 

[Streak!]

I think the DD coil is a fair amount better at isolating/IDing iron than the concentric.(due to its tighter footprint) Despite what coil you use though....you will get a few that will fool you, no matter what coil or machine you use. (Things like plow points.....round iron rings.......etc..)
I've found over the years that finding the exact center of the target helps a lot when trying to ID iron, as does a fast sweep speed over the exact center. Iron for the most part will be a lot louder and harsher than a coin or similar target too. Using the pinpoint mode gives me better and more reliable info than disc mode does! When you pinpoint...iron will "ramp up" faster than coins will when you approach the target, and again sound louder and harsher. (Especially shallow iron). Pinpointing will help you tell the shape of the target too. (Nails usually sound a lot different with sweeps 90 degrees apart). The spread of the VDI (this was mentioned in another post here somewhere) is a big clue too. Good targets tend to have a lot smaller spread on the VDI than iron will. In time, you'll get a feel for whats under the coil.....but even the seasoned veterens get fooled now and again!!!