Air tests

Was wondering do air tests on coils really represent the depth in soil? thanks in advance

I have seen on vids air tests that pretty well are same as the coil size, ie a 15" coil air tests at 15"

I relise there are many factors but in general does depth equal size of coils.

guvmore Wrote:
-------------------------------------------------------
> Was wondering do air tests on coils really represe
> nt the depth in soil? thanks in advance
>

No...but we all wish they did.
A simplified rule of thumb is that higher frequencies air test better but are more adversely affected by the ground.

>
> I relise there are many factors but in general doe
> s depth equal size of coils.

Some modern detectors/coils can easily exceed the coil diameter in air tests.

One would think an air test would represent the maximum depth that could be achieved. To attain the same in ground, it would need to be neutral soil, but then things like ground moisture come into play which I believe from personal experience can help go beyond depths of even air tests. Also how long the object's been in the ground and the type of ground (ie clay, soil, etc) can have an affect. I remember digging a v-nickel at over 10 inches in black soil with a Whites machine that it would've never air tested at.

Then there are machines that don't air test well but get good depth in ground. Minelab's come to mind.

The experts have more info on this but I don't put a lot of stock in air tests for those reasons.

HH
John

P.S. Hadn't considered the operating frequency as mentined above but I guess that plays a role too.



Edited 1 time(s). Last edit at 02/08/2017 07:09PM by DirtyJohn.

DirtyJohn Wrote:
-------------------------------------------------------
> One would think an air test would represent the ma
> ximum depth that could be achieved. To attain the
> same in ground, it would need to be neutral soil,
> but then things like ground moisture come into pla
> y which I believe from personal experience can hel
> p go beyond depths of even air tests. Also how lon
> g the object's been in the ground and the type of
> ground (ie clay, soil, etc) can have an affect. I
> remember digging a v-nickel at over 10 inches in b
> lack soil with a Whites machine that it would've n
> ever air tested at.
>
> Then there are machines that don't air test well b
> ut get good depth in ground. Minelab's come to min
> d.
>
> The experts have more info on this but I don't put
> a lot of stock in air tests for those reasons.
>
> HH
> John



Minelab is what prompted my post, I air tested a few items and was dismal but know they go deep on silvers, anyway it is on Ebay. It pretty well went null on clad...time to update.

High Freq high gain machines can air test to the moon at times...

Yet are lucky to get half that distance in the ground...

BUT a low freq may not show tremendous air test depths but may in the soil hold 75 percent of that air test depth.

so it seems once the soil is in play the depths get closer together..

and usually a coil above say 12 or 13 inches on any unit on coin sized objects starts to suffer in terms of seeing coin sizes at times as deep as say a 10 inch coil ....a large coil likes large targets and small coils like small targets and the stock coils are usually the coils that are designed to see the best on a coin at depth fro that platform

FTP changed the playing field quite alot when the developed What I still consider a ground breaking coil design that basically opened the doors for a flood of high performance DD's from after market company's and even Garrett and so on..

the bi axial gave DEPTH and SEPARATION...


Keith

“I don't care that they stole my idea . . I care that they don't have any of their own”
-Nikola Tesla

I'm getting the feeling maybe mid size coils sniper too small and a Wot type coil to cumbersome...

guvmore Wrote:
-------------------------------------------------------
> I'm getting the feeling maybe mid size coils s
> niper too small and a Wot type coil to cumbersome.
> ..

It is not unusual for some machines to airtest a Twice the diameter of the coil on coins and I have dug coins at over 30 to 40% deeper than the size of the coil, I my soil I loose about 10 to 20% at the very most compared to my air test depths.

Agree with Keith, the 11" Biaxial had some early teething problems but is now one of the best stock size coils ever made.
Tom

____________________________________________________________________________________________________________
In a democracy, it is difficult to win fellow citizens over to your own side, or to build public support to remedy injustices that remain all too real when you fundamentally misunderstand how they see the world.

Keith Southern Wrote:
-------------------------------------------------------
> High Freq high gain machines can air test to the m
> oon at times...
>
> Yet are lucky to get half that distance in the gro
> und...
>
> BUT a low freq may not show tremendous air test de
> pths but may in the soil hold 75 percent of that a
> ir test depth.
>
> so it seems once the soil is in play the depths g
> et closer together..
>
> and usually a coil above say 12 or 13 inches on an
> y unit on coin sized objects starts to suffer in t
> erms of seeing coin sizes at times as deep as say
> a 10 inch coil ....a large coil likes large targe
> ts and small coils like small targets and the stoc
> k coils are usually the coils that are designed to
> see the best on a coin at depth fro that platform
>
> FTP changed the playing field quite alot when the
> developed What I still consider a ground breaking
> coil design that basically opened the doors for a
> flood of high performance DD's from after market c
> ompany's and even Garrett and so on..
>
> the bi axial gave DEPTH and SEPARATION...
>
>
> Keith


Keith back in the middle 70's Garrett made a "stacked" coil for their VLF Deep Seekers--the frequency was around 2kz and the coil didn't pick up off the top---Is this what you are calling a "bi axial coil? Thanks.

Hey Doc!!

What I meant was the Coils developed since the 11" Bi-Axial FTP design...seems everyone jumped on board with a New radical DD even Garrett with the Blunt Tip 8x11 on AT-PRO..

Coil design has really came into its own and it was I feel Fueled largely By FTPs Bi-Axial..a Dave Johnson Design I believe also.

Remember when that coil ((Bi-Axial)) was first seen it was like no other and a BIT ODD..now its the NORM to have drastic looks in coils appearance..

Speaking of old school Garrett wasn't that a Co-plainer??or something?? that didn't pick up on top...I still notice the garrett 4.5 Concentric doesn't like to receive above side on the AT series... ..

Do you remember that Garrett BFO coil that had a switch for like 4 or 8 or something..had a small coil in middle and to the rear of a big coil....you could switch between loops...of course you could get away with that in a BFO design..not happening in VLFs..LOL..would be neat to switch coil sizes on the fly!!

Keith

“I don't care that they stole my idea . . I care that they don't have any of their own”
-Nikola Tesla

Keith Southern Wrote:
-------------------------------------------------------
> Hey Doc!!
>
> What I meant was the Coils developed since the 11"
> Bi-Axial FTP design...seems everyone jumped on boa
> rd with a New radical DD even Garrett with the Blu
> nt Tip 8x11 on AT-PRO..
>
> Coil design has really came into its own and it wa
> s I feel Fueled largely By FTPs Bi-Axial..a Dave J
> ohnson Design I believe also.
>
> Remember when that coil ((Bi-Axial)) was first see
> n it was like no other and a BIT ODD..now its the
> NORM to have drastic looks in coils appearance..
>
> Speaking of old school Garrett wasn't that a Co-p
> lainer??or something?? that didn't pick up on top.
> ..I still notice the garrett 4.5 Concentric doesn'
> t like to receive above side on the AT series... .
> .
>
> Do you remember that Garrett BFO coil that had a s
> witch for like 4 or 8 or something..had a small co
> il in middle and to the rear of a big coil....you
> could switch between loops...of course you could g
> et away with that in a BFO design..not happening i
> n VLFs..LOL..would be neat to switch coil sizes on
> the fly!!
>
> Keith

Keith, as usual you are correct---it was called a co-plainer coil,but also was called a "stacked " coil because it was about twice as thick as a regular coil. Was only about 8" and was d eeee p. Never used the Garrett BFO,but can still remember the putt,putt. Ahh the Good Ole Days.