Air Tests...

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Bargeman
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Air Tests...

Post by Bargeman » Wed Mar 01, 2017 8:21 pm

I have been thinking again (I should be banned from thinking) and as it happens watching too much YouTube again, but I am curious, do all these air tests people do with a new coil, actually have any real benefit when you take the coil to the field. Or is it all just smoke and mirrors, giving you a false feeling of depth superiority. And do the depths found when waving a coin in front of a coil in your kitchen, bear any resemblance to what the coil can actually do?

I can't do air tests, my home environment won't allow me that option, but I do seem to be digging smaller items deeper with my Tornado, than I am with my 9" XP coil, but is that the coil or the damp weather we are getting, the only way I could know for sure would be to have two machines the same, fitted with the two coils, and check a find with both before digging?

:-/


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nellyt5
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Re: Air Tests...

Post by nellyt5 » Wed Mar 01, 2017 8:38 pm

I'm sure we all do air tests at some point, maybe to set up the machine for best results for depth or to see how they react when a rusty nail is thrown into the mix etc, but are these chosen settings effective out in the field , ive no idea,
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Re: Air Tests...

Post by sweepstick47 » Wed Mar 01, 2017 10:30 pm

There should be no confusion......assessing either the sensitivity or depth potential of a search-coil on any detector by means of an 'air test'' will not give an indication of the coil's depth performance 'in the field'.

In my limited and dimly lit understanding, it seems the only way to obtain a notable depth increase from any detector/coil, would be to produce the means to amplify the residual current flow on the surface of the target, (without increasing the power of the transmitted magnetic search field) thereby making the target signal easier to 'see' by the coil's receive winding. ??
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fred
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Re: Air Tests...

Post by fred » Wed Mar 01, 2017 10:42 pm

It may not give much of an indication about depth but it will about sensitivity. ::g

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Re: Air Tests...

Post by Wigeon » Thu Mar 02, 2017 8:30 am

I am still a relative newcomer to metal detecting, however I have spent three or four days a week with my X-Terra and E TRAC for the past six months.

I have air tested my coins and buttons at home and they nearly all come up on the 12 line for ferrous. In the ground those same items very often came up as something completely different.

I have also discovered that the depth indicator is of limited use when different sizes and shapes are detected.

I had read much about learning the audible tones/volume etc. and that they are the most reliable indication of target depth, size and type. Having now dug hundreds of holes, I know that is oh so true.

I am now at the stage of wondering why manufacturers provide screen indications and depth indications because they are of so little use in practice. I now understand how experienced detectorists can use the Deus Lite, as that had previously been a mystery to me.

Six months ago I could not imagine that I would be writing such a post as this. At that time I was firmly glued to the screen and depth indicator, when a signal sounded. Lots and lots of digging has cured me of it though. I suppose one has to do the digging to gain the experience that has brought me to my current position ?

I no longer air test my finds as I see no real benefit in so doing, other than for fun or curiosity.
Just my experience so far, so hope it is useful.

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Re: Air Tests...

Post by Count de Washers » Thu Mar 02, 2017 9:25 am

Agree with the above, but cannot air tests be useful for comparing detectors/coils against each other? Forget the measured (as in inches) air depth of course, but can you not say that coil A is 25% more sensitive to that particular target that coil B, so the measurement is not actual inches but just relative and expressed as a percentage? Trouble is I suppose that in the soil that percentage difference may not be repeated - Oh well lol.

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Re: Air Tests...

Post by redwulf500 » Thu Mar 02, 2017 10:01 am

hi my view is whatever it air tests at , it will never go deeper in soil and that goes for all detectors ..

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Re: Air Tests...

Post by Koala » Thu Mar 02, 2017 1:07 pm

redwulf500 wrote:hi my view is whatever it air tests at , it will never go deeper in soil and that goes for all detectors ..
Agreed with any VLF you will never go deeper than it air tests. Regardless of what people write about wet ground.

I find dry powder sand depth to be very close to air tests

Generally wet ground loose less

Occasionally you will dig an artefact or coin deeper than it can air test. Its not magic, its not halo unless its iron. Its just something else nearby whether coke granite brick tile which adds to the signal.

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Re: Air Tests...

Post by Fusion » Thu Mar 02, 2017 1:19 pm

Quote:"I am now .. wondering why manufacturers provide screen indications and depth indications because they are of so little use in practice."
Some comments here:
viewtopic.php?f=10&t=89720

Airtest distances are useful for comparing with other people's figures. Eg. If you say your TekLab 2000 will detect a Pound coin at 14 inches, and my one can only manage 10 inches, maybe I need to check my machine, see if water's got into the coil, etc.
:(

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Re: Air Tests...

Post by Koala » Thu Mar 02, 2017 2:07 pm

Count de Washers wrote:Agree with the above, but cannot air tests be useful for comparing detectors/coils against each other? Forget the measured (as in inches) air depth of course, but can you not say that coil A is 25% more sensitive to that particular target that coil B, so the measurement is not actual inches but just relative and expressed as a percentage? Trouble is I suppose that in the soil that percentage difference may not be repeated - Oh well lol.
Sort of.

Testing a detector is not simple. Several classic detector only air tests average but preforms better in mineralized ground than most others (don't want to get into brand bashing)

As an example I built a coil for my IDX. I can change a capacitor inside and it will alter its depth.

Starting 35 cm on a pre decimal penny to nearly 50 cm. However I leave it at 35 cm.

Why I can hear you say. Well at 50 cm the coil became unstable. Discrimination is worse and on most ground depth is less.

So no 25% more in air doesn't always mean more in the ground but may do.

Even a test garden isn't normally the same as finding thing in the field. First you know where the targets are. Subconsciously you alter your swing and home in on targets that you would probably walk over in the field. Most fields are a big jumble iron coke with coins lying in any orientation.


Give you another example

Couple of iron nail near the surface with a small coin lower between them

Run a concentric coil down the nails and it doesn't pick up the coin.
Change to a DD and it does.(as per many YouTube reviews)

Ha ha DD is better at finding coins under iron.

Nope try the same test but swing at 90 degrees and the results are reversed.

Watched some Scottish lads on a rally in Yorkshire. Everybody else ground balanced and started detecting. They dug a hole a buried some coins to test there machines and settings were working well on that day and in those conditions.

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Re: Air Tests...

Post by Koala » Thu Mar 02, 2017 2:16 pm

Fusion wrote:Quote:"I am now .. wondering why manufacturers provide screen indications and depth indications because they are of so little use in practice."
Some comments here:
viewtopic.php?f=10&t=89720

Airtest distances are useful for comparing with other people's figures. Eg. If you say your TekLab 2000 will detect a Pound coin at 14 inches, and my one can only manage 10 inches, maybe I need to check my machine, see if water's got into the coil, etc.
Agreed


Same machine, coil and settings should be in the same ballpark air testing.


There might be a small discrepancy due to manufacturing tolerances.

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Re: Air Tests...

Post by Bargeman » Thu Mar 02, 2017 5:57 pm

Some interesting relies here, thanks all... ::g
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Re: Air Tests...

Post by Spiker1968 » Thu Mar 02, 2017 7:12 pm

The internet is full of people waving things in front of their metal detector, even burying things in their garden and finding them over and over again. Can't help thinking if they spent all that time and effort waving it over a patch of land instead they might actually improve their chance of finding something. Just my cynical side coming out!
:-/ :D

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