Any Value in Air Tests?

[WhatTheBeep]

I've only been metal detecting a year, but I know there are many of you here that have a wealth of knowledge on the subject, so I thought I would ask. I've heard and seen numerous times that air tests don't tell anything about a metal detector's ability, but now I'm wondering if that's the case.

I got a new F70 yesterday and got to play with it quite a while today. After a few hours of actual metal detecting I thought I'd see what various sens and thresh settings would do in terms of air test depths on some coins I'd found. I was surprised to find that sens and thresh didn't make nearly as much difference as I thought they would, but SL speed and Autotune seemed to make a significant jump in how far a penny could be detected.

My question is: under normal circumstances (dirt graph showed 1 bar and ground grab value was 65 and there was no noticeable EMI) can a metal detector detect a target in the ground at a greater distance than the same target in an air test (a coin not on edge for example)? So if I get 10" on a penny in an air test I'm not going to get more than 10" on a penny in the ground under normal conditions, correct?

 

[Southwind]

There are always exceptions to the rule but generally I believe the depth you get in the air is the maximum you can expect in the ground under perfect conditions. That being said, some detectors do not air test well which means the rule does not always apply. I know that doesn't help much but it is what it is.

For me depth is tested not by how deep a detector can see a target but how deep a detector can accurately tell the user a deep coin exists. All mid to high end detectors can get pretty much the same depth if they have the same sized/type coil. The difference is not all detectors can accurately tell the user when a 8" coin is under the coil without years of experience with that detector.

 

[MarkCZ]

With a new machine air testing is more worth while, its helps with sounds and settings. I do us it for somewhat of an idea for depth on coins and jewelry, but by no means the real end results. In most ALL cases except with relics and rusty iron I get the most depth while air testing, so, If I can get 10" of depth when air testing a dime I don't expect to any more depth on a dime in the ground, in my case its never been anymore. So, if I air test a detector on a dime and I only can get 6" and I believe its not broken then I know I'm not going to be able to use it for the old coin hunting I do.

Mark

 

[Mike Hillis]

I've experienced situations where I have detected coins deeper than they air test. These were cases where the ground conditions enhanced the coin's response, as if the ground made the coin seem larger, and so it was detectable at a deeper depth than that same coin could air test.

So yes, it is possible to detect a coin in the ground (as well as other things) deeper than it air tests.

HH
Mike

 

[WV62]

I don't think air testing is good for every type of hunting, but for coins I think it gives you a good idea of the max depth you could expect to find a coin in the ground. I test other coins but for me a clad dime is the only one I really need to test, if I can hit that I can just about expect to hit anything in the higher disc range.

I like to tweak all my settings to the max depth in air testing to get some good numbers to start with in a real hunt. I attached my latest test of my F75 and you may notice that I got a big jump in depth on coins by running up the disc to max and notching in items like the nickel.

Ron in Wv

 

[Elton]

Air test only gives you a reading of coins on metered machines in a perfect scenario ..... On beep and dig it gives a perfect distance beep..

Put those coins in the ground and you will get some variance due to minerals, angle of coin in the ground, and substances between you and the coil will effect the detection accuracy.. Depth of the coins will alter the reading too..

Fun to play with on a snowy day .............. Think of it only as a demo value ..................

 

[WhatTheBeep]

Thank you all for your answers. I'm trying to digest as much as I can to try to learn this new machine -- what it'll do and what I can expect from it under different circumstances. I've read a lot about it the last month or so, but it's not quite the same as actually getting some hands on experience, for sure!

Interesting about the relics sometimes being detected deeper in the ground, Mark.. I figured sometimes the ground conditions could make this possible even for coins. Also, a very interesting chart, Ron -- especially that you can get more distance with more disc which is something I'd heard didn't usually occur.

Thank you all again.

--WTB

 

[MarkCZ]

Thank you all for your answers. I'm trying to digest as much as I can to try to learn this new machine -- what it'll do and what I can expect from it under different circumstances. I've read a lot about it the last month or so, but it's not quite the same as actually getting some hands on experience, for sure!

Interesting about the relics sometimes being detected deeper in the ground, Mark.. I figured sometimes the ground conditions could make this possible even for coins. Also, a very interesting chart, Ron -- especially that you can get more distance with more disc which is something I'd heard didn't usually occur.

Thank you all again.

--WTB

Well, relics can be of all sort of metals and some metals will "Halo" far more than others. Anything like Iron that can rust or even heavily corrode will leach their minerals out into the soil around the object and to the detector the target will seem MUCH larger than its actual size.

I have found greater depth hunting coin in slightly dampen cooler soil, but to date in our WV soil I've not found a coin deeper than I can air test them, but! different conditions and different soils causes or creates different results.

Mark

 

[Rainyday101]

Air is a great medium to transmit a VLF signal through, ground is not and will have higher signal loss due to reflection and absorption. So in theory the short answer is your air test should exceed in ground depth. Now that is theory, and as stated above the right ground conditions, soil, type, and dampness might somehow aid the coin's response. Even though it would seem not likely there are too many people that in the right conditions have claimed to have gotten deeper, so I gotta believe it is possible, but not the norm. The only time I have matched my air test has been on coins in wet sand. Note that is freshwater sand I am talking about.

As WV62 said, all really gotta test is a dime.

Also as mentioned above, the air testing for depth is only good on coins because coins do not produce a halo effect.. Some say a copper penny will, but it is negligible compared to rust halo iron can leave.

 

[mudpuppy]

Just turn it on and go dude..all the above replies are valid...problem is, theres just no experience like real world dirt time for teaching...dont sweat the details...swing speed has a lot to do with the F70's depth range too...try it on a coin out in the yard...you can really whip that coil over it quick and high and get a peep...too slow and you wont...it takes at least 10k targets recovered in the real world for a guy to get to understanding the language...so go out there and dig 10k targets as fast as possible and you will condense theory into practice in a gosh darn hurry! Then its site reading and strategy and timing that becomes important, and not depth etc...My mentor told me to "dig 1000 pulltabs and dig 1000 pennies, as fast as you can...like in a month....guess what? you get real good real fast when those are your only goals, and you also find a lot of other things along the way..like gold...time and gold wait for nobody, so get out there and flail away with that 70 heater! It will not let you down!....
Mud

 

[WhatTheBeep]

I see the wisdom in that... "Wax on, wax off", to quote an old movie. Thanks, Mr. Mud, I'll aim to do just that!

 

[metalfun]

Just turn it on and go dude..all the above replies are valid...problem is, theres just no experience like real world dirt time for teaching...dont sweat the details...swing speed has a lot to do with the F70's depth range too...try it on a coin out in the yard...you can really whip that coil over it quick and high and get a peep...too slow and you wont...it takes at least 10k targets recovered in the real world for a guy to get to understanding the language...so go out there and dig 10k targets as fast as possible and you will condense theory into practice in a gosh darn hurry! Then its site reading and strategy and timing that becomes important, and not depth etc...My mentor told me to "dig 1000 pulltabs and dig 1000 pennies, as fast as you can...like in a month....guess what? you get real good real fast when those are your only goals, and you also find a lot of other things along the way..like gold...time and gold wait for nobody, so get out there and flail away with that 70 heater! It will not let you down!....
Mud[/qu

THANKS FOR THAT RESPONSE MUDD.ONE OF THE BEST.

 

[markg]

All very good points. In neutral ground and near zero EMI, air test and in ground depth can be identical, but add mineralization/a little trash and EMI and that can be cut in half. I might add one thing, air test gives the user an approximate coil to target distance, so I carry at least one coin with me while I'm hunting and if I feel the performance has been down graded I perform an air test on the spot. Even if I can't determine if EMI is present the air test will reveal any problems if they are present. Remember, even if you can't hear EMI (coil still in the air), it doesn't mean it's not there.

 

[Steve O]

Markg, I do the same thing... to check...especially with the cz.

 

[WhatTheBeep]

Thanks MarkG, that's great information.