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
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
I hope there is something in these charts of air testing results that will help in your setup of your F5.