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F series depth air to ground
Posted by: WV62
Date: March 26, 2017 10:38AM
I am posting this question here because my primary machines are all F series machines and the same for my 2 brothers.

So most of you know I do a lot of air testing, but I get some feed back saying it is pretty much useless except to see if a detector is working.

Now I would like open this up to both sides pro and con. One of the things I see posted from time to time is a detector will detect deeper in the ground than in the air. The only way I can see that happening is the halo effect which makes the target actually larger in the ground than when you pull it out. So outside of that I don't see how any ground could help a detector see a target deeper than in the air.

So I am hoping somebody out there can prove or disprove the air to ground issue.

Please note, I am not looking for a fight.

Thanks,

Ron in WV



Worked and lived in the Huntington West Virginia area all my life, retired 2010
US Air Force Vietnam Veteran (68-69 & 70-71)
Started getting into metal detecting around 1975



Edited 1 time(s). Last edit at 03/26/2017 10:46AM by WV62.

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Re: F series depth air to ground
Posted by: still looking 52
Date: March 26, 2017 11:33AM
Dirt is denser than air which will cause the distance to decrease in depth. That's how I see it.

Re: F series depth air to ground
Posted by: doc holiday232
Date: March 26, 2017 02:18PM
Air tests are valid indicators of the capabilities between 2 machines of the same brand.

Air tests also can give an idea of the capabilities between different brands of machines. I KNOW some machines don't air test well,but I am speaking broadly.

I would take the machine that air tested over another machine.

Charles Garrett himself told me in 1974 that an air test would Definitely show WHICH machine was superior when comparing machines of the Same Brand.

Re: F series depth air to ground
Posted by: jim tn
Date: March 26, 2017 02:33PM
The only thing I see air tests good for is serving as a barometer for one to determine if their detector air tests more or less then other like detectors or to compare against other brands/models. I've had 3 F 75's that air tested a dime 10-10 1/2" and I have never dug a dime deeper then 9". And 9" is a rare instance. And I chase some of those 11" and 12" depth readings. Which, would put some coins in the 9-10" range the way the 75's depth read. HH jim tn

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Re: F series depth air to ground
Posted by: MarkCZ
Date: March 26, 2017 03:09PM
Most soils (real dirt) has different amounts of minerals in them hence the different ground read numbers, so in any case minerals reduce the depth effectiveness of a metal detector. Someone on this forum stated it like this,
Ground minerals are to a metal detector what driving fog is to car headlights.

Now, there has been on occasions where I found a target deeper than I expected, but I don't think I've ever found a coin deeper in the ground than in an air test. The deepest thing I guess I ever dug that I thought was a coin turned out to be an antique Ford round screw on axle cap (it would be called a hub cap in current time) it was probably near the 12" range.

Mark

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Re: F series depth air to ground
Posted by: dfmike
Date: March 27, 2017 10:23AM
Air testing can at least reveal if a coil is faulty or incompatible. I bought a Nel Tornado for my F5 once that air tested about a third as "deep" as any coil I had tested before with any target. I couldn't get anything to test beyond about 4 inches.



Active detectors: Fisher F5 , Fisher F19 LTD, Nokta Fors CoRe, Makro pointer and way too many coils.
Previous detectors: Bounty Hunter Discovery, Fisher F44, Omega 8000 V6, Minelab X-Terra 705

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Re: F series depth air to ground
Posted by: WV62
Date: March 27, 2017 11:20AM
So far so good, all good stuff.

I do a lot of coil comparing on my F75 and then kind assign each a type of hunting or a site that I think needs the attention of one of my coils.

Thanks,

Ron in WV



Worked and lived in the Huntington West Virginia area all my life, retired 2010
US Air Force Vietnam Veteran (68-69 & 70-71)
Started getting into metal detecting around 1975

Re: F series depth air to ground
Posted by: WhatTheBeep
Date: March 27, 2017 12:15PM
Air tests are important to me for a lot of the above-mentioned reasons. It lets me know that my machine and coil are working properly and it's also a good indicator of silent EMI. Agreed that jumping from one brand to another isn't as helpful, but when you already have a baseline for what your individual machine can do it can be helpful.

I'm no expert regarding detecting further in the ground than in the air, but I believe it's possible at times. As you said, when a target has leached out and presented itself larger than it is, for one. I also believe under some rare circumstances the current conductivity state of the soil can make this possible (i.e., the right amount of moisture, proper quantities of mineralization, etc.), but I have not experienced such a situation myself.

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Re: F series depth air to ground
Posted by: MarkCZ
Date: March 27, 2017 01:50PM
Other things can happen doing air test that slips by the operator when their actually in the field detecting,
Like with me and my F70,
I really didn't know if it had modulated audio or not! the manual don't say! sometimes the headphones I use with a volume limiter can block some of the effect of modulated audio.
it wasn't until I did a step by step settings change that I discovered that there is setting points that flip the modulation on and off like,
SL mode seems to be Non Modulated!
A threshold setting of 0 or below in DE mode is non modulated audio, but at +1 or higher its modulated audio (not in the manual)

Its hard to impossible to find these kinds of things out about a detector while we're hunting in the field, different kinds of soil, unknown buried items (you can't see) like underground pipes, car parts, cans, sinkers, wheel weights, underground wire and many times this stuff is clustered with thousands of other common metal trash items. So, in the field its harder to determine what's the detector and what's in the ground effecting the detector. Air test takes out those in-ground variables because it can be set up to take out everything between the coil and the target, or to say the test can be staged to near PERFECT condition not possible to achieve in the field. Targets are held as paralleled to the coils as possible, if its tilted or slanted its done as part of the test, if masking happens its part of the test, same for close proximity targets.

And Ron and I both have determined that buried test gardens are also not great as compared to real field hunting and if we can't come up with a better way to plant a target then doing so beyond about 4" inches can cause you to just lose the coin for a number of years, if not forever. I've got three 7" nickels that I buried probably 4 years ago and they're just GONE! I'd say knowing where they are I could probably take the F70 in ALL-Metal and get a hit on them but If I turned you lose in my yard in All-Metal you would probably have to dig three or four thousand holes before you found all three of them.

So, the phrase air test are worthless and don't do anything compared to real world hunting is true on one side because air test are STAGED TO AS NEAR PERFECT CONDITIONS as possible to get the best possible target response from the detector as possible, in the field every imperfection, every variable interferes with the detectors capability, it doesn't improve it, yes the electronic filters and other magic electronic trickery is design to help us the operator to work around these problems in the field.

Air testing is the BEST way to get a feel of what your detector CAN do, that gives the operator a feel for the detector and then field experience gives them the best handle on dealing with the real world variables.

Here is another case where I discovered a detector/coil fail. I won't mention brands because I don't believe it was a brand specific problem, or to say you won't know if you don't air test. I had this modern day detector with a 11" DD coil that worked fine, but I had heard that the 5" DD coil was just magic and so I had to have one. Well without air testing it I just went hunting, well the learning curve was difficult to say the lest but I had some head scratching moments that led me to do some air test and the one thing that I found out was that a dime slightly tilted or slanted would just disappear at about 4" from the coil :shrug: I went back to the 11" coil and gave up on the 5" altogether.
Now I bet you have some questions about that super duper little coil you like so much, have you been digging as many tilted coins as you used to, you know the ones where you dig a plug and you can see the dime or penny in the side of it tilted? you'll only know if you air test and angle the coin as it passes the center of the coil. (No This Wasn't My F70, but If I had a 5" coil for it I would test it to make sure it didn't have the same problem)

Several years ago some detector manufactures went though a problem with detectors that would NOT detect a US Silver Dollar in discrimination mode!! Well, it seems that what was happening was the upper discrimination range didn't have enough room for the Silver dollar! so its my understanding that the detector was detecting them but they were coming in very low in the Iron range. Got an older detector, you might want to do an air test with a silver dollar!

How many of you have been to a pretty well worked out area and found small pocket spills of coins? the most likely reason for me is field experience! un-experienced hear the multiple rapid responses has a discrimination breaking up (junk item), I hear them as multiple close proximity targets with at lest one or more good targets in the range that I'm looking for!

So, NO!! air test will never EVER out do an extremely seasoned detectorist. Here is a NEVER DO! don't get a new to you super Hot Rod detector and go out to show up this older guy with his 20 year old detector that he uses 20 hours a week sense he bought it new! your likely going to end up looking like a fool and wanting to throw your detector over the hill, or sending back for service.

Mark



Edited 1 time(s). Last edit at 03/27/2017 02:05PM by MarkCZ.

Re: F series depth air to ground
Posted by: doc holiday232
Date: March 28, 2017 09:29AM
Mark--great info on tilted coins. Thanks.

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Re: F series depth air to ground
Posted by: MarkCZ
Date: March 28, 2017 10:53AM
Quote
doc holiday232
Mark--great info on tilted coins. Thanks.

Well "doc" that most likely was a fluke but if I was to ever get a 5" DD coil for my F70 I would for sure air test to make sure it passes that test, in fact I do have the little football coil for it now so its probably a good idea to test it before I just assume a tilted coin don't mess with it.

Here is another fail that my brother found just playing around for fun, so it was an accident and could be included as an air test result. He has this good size bag of silver coins that he's collected over years and years, so the idea was to lay the bag and all on the ground so the coins stayed in a pile and see what the detector response sounded like going over a cache of coins, I mean its everybody's dream who owns a detector to find a cache of silver coins right!!!!! Well, it FAILED! absolutely NOTHING! now I'm thinking that was in discrimination mode and at this point he remembers that happening but he don't remember which detector it was. After talking to him about that I've got a feeling pretty soon he'll be doing that test again.

How, many here has a taken say a sock and put a good size hand full of silver coins in it and tested their detectors to see what response they got? how ticked off would you be if for the last year or so you've been dreaming about that mother load and your detector or the settings your using won't even hit on a cache of coins!!, or maybe the response would be more like the response you would get for a piece of large rusty pipe?
Well, that's like the big silver problem that turned up a few years ago, I mean for many finding a silver dollar is a bucket list item and it turned out there detector wouldn't even hit on a silver dollar! at all (in discrimination mode).
A spread out pocket spill is one thing, a piled up cache is another.

Mark

Re: F series depth air to ground
Posted by: doc holiday232
Date: March 29, 2017 11:12AM
WOW--on the sack of silver coins. Hope Brother will repeat his test and report on it. I hear that a pile of gold dust won't be detected by a gold detector,but the silver coins are thousands of time larger than a spec of gold. Keep us posted.

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Re: F series depth air to ground
Posted by: MarkCZ
Date: March 29, 2017 12:48PM
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doc holiday232
WOW--on the sack of silver coins. Hope Brother will repeat his test and report on it. I hear that a pile of gold dust won't be detected by a gold detector,but the silver coins are thousands of time larger than a spec of gold. Keep us posted.

That's the same problem as tiny linked gold chains, to the detector the links are detected as separate links. So, unless the detector could actually detect a single link of the chain its no more likely to detect the entire chain, unless the chain has a larger clasp or a larger pendent with it the detector will just pass it up. Here is something else interesting. A gold ring if its band is solid and fully connected will give a good response to a metal detector, cut the band and form a gap in it and the detector may not respond to it at all!!
This is getting in over my head but it has something to do with what they call "eddy Currents" flowing a continuous loop and not being able to if the loop is broken.

Mark

Re: F series depth air to ground
Posted by: doc holiday232
Date: March 29, 2017 04:41PM
Interesting on the whole ring vs. the cut ring. If you do anymore tests keep us informed.

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Re: F series depth air to ground
Posted by: WV62
Date: March 29, 2017 06:41PM
Here my follow up to the bag of silver my brother was talking about. Now I did do that test again and my current detectors F75Ltd upgrade for the DST and my F5 both will high tone on the $100 face value bag of old silver coins. The F75 ringing in at about a dime and the F5 was saying quarter, both went into overload with the coil close to the bag.

Now I did that test in the not so far past, so it was either with my current F75 before the upgrade or the F75LTD that I had before the one I have now.

I know the F5 that I sold my brother wouldn't hit on a silver dollar in disc mode. He sent it back to FT and they adjusted or whatever and fixed that problem.

So it wouldn't hurt to check your machines on some big silver.

I am currently working on a chart of air testing on my F5. I am seeing what a sliver dime will do at all levels of threshold compared to all levels of Gain. I started with the 5" DD coil and I am about 3/4 complete with that one. Then I will do the same test with the 11"DD coil. Lots of testing to get through this test, but I will post each chart as I finish them.

So if you can't wait set your F5 to threshold -1 and gain about 70 that is my hottest so far for the 5" DD coil.

Ron in WV



Worked and lived in the Huntington West Virginia area all my life, retired 2010
US Air Force Vietnam Veteran (68-69 & 70-71)
Started getting into metal detecting around 1975

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