Air Test Question - F75+

[GrantT]

Hello all,

This is a general question I guess about air testing, but perhaps more specific to my unit or model (Fisher F75+), but I've noticed many videos etc. where people are air testing their detectors to get some sort of feedback and often easily hit 12" etc depending on the coin/object used.

I've tried this with both my stock 11" coil and a Magic 5x8 I picked up, and I noticed that NEITHER will seem to respond to a coin (penny) after about 6".

I understand the air test is not necessary indicative of real performance, but it seems like just isn't picking up properly. Is there any way to test/confirm if a machine is functioning properly? Anything I can/test to do? I do have some buried coins etc, but nothing deeper than 6".

Grant

 

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[Charlie P. (NY)]

I was never sure how to ground balance for air so I avoid the practice.

Indoor air tests with an F-75 are pointless. Too much EMI.


If you have a coin 6" deep in the yard try lifting the coil 3" or 4" off the soil as you sweep.

 

[GrantT]

Yeah, the problem I am seeing is that the 5x8 coil is not even detecting the 6" coin when the coil is on the ground...that's why I started testing. Perhaps that is to be expected? Being a novice, I just don't know what is "typical" etc.

 

[HighVDI]

Per directions from Tom Dankowski.

Your F-75 on sens. 90, in PF mode or DE process should sound off clear and ID a 10" clad dime without issue with the stock coil.

This is outdoors and away from any EMI or ground mineralization. If not, I would contact First Texas to see if they could give the unit a once over...

 

[Loco-Digger]

Something isn't right. Do a factory reset and try again..

 

[Iffy Signals]

I get everyones feedback on air tests but they do have there place. Whenever i get a new machine i run some air tests to learn VDIs and an average for depth on each setting. Just cant do them with to much EMI. I like spending a couple days at a park without EMI running some air tests and hunting clad to get a feel for the machine. Trying to learn a new machine on relic sites is painful.

 

[HighVDI]

Sorry. Edited my post above...butchered it...

 

[GrantT]

Thanks.

I'm going to grab a few coins, head out to a field, bury them and do some additional testing to see what comes back on the unit.

I've reset to factory settings numerous times (between coil changes etc).

Will report back. Thanks for the suggestions all....

 

[GrantT]

So, this is likely just my lack of experience with metal detecting so please bear with me....

Out in my regular stomping ground (ball field) and did some testing. I dropped a dime, and then a penny (both laying flat), into an 8" hole and covered them up and both were strongly and immediately detected. OK...that seems great and offsets my worries about the poor detection depth in my own yard. The detector also got the depth pretty accurately.

So this leads me to a couple more questions I can't seem to find the answers to:

1) The dirt/sod/clay in my yard requires me to ground balance at around 35. Does this mean the soil there is very low mineral? If so, does low mineral soil explain the poor depth detecting etc in my yard - i.e. the F75 seems much less sensitive in my own yard when compared to the ball field, which ground balances in the low 50s.

2) Why, when I run across the numerous other pennies/coins etc, does the detector depth read as usually 6" when I pinpoint, when they almost always only 1" - 2" down? Something to do with the way the coin is sitting? i.e. at an angle, or more vertical? These all tend to be older pennies where in Canada, prior to 1997 the one-cent coin was 98% copper, 1.75% zinc and 0.25% other metals.

3) I've read in some F75 notes online that someone mentioned "that if you set the Disc lower than 5 or higher than 19 the detector runs at a higher gain in DE processing". Is there any way to verify this is an accurate statement? I don't see that documented in the manual. If it is true, does anyone have any suggestions for settings for a "general purpose" go-to setting for ball fields. Unfortunately, lots of foils, caps, tabs which SEEMS to be exactly where the Canadian clad coin and the silver necklaces etc I've found come up.

 

[HighVDI]

When you GB look at the FE meter and see how many bars are illuminated. This will tell you how hot your dirt is.

 

[digger27]

3) I've read in some F75 notes online that someone mentioned "that if you set the Disc lower than 5 or higher than 19 the detector runs at a higher gain in DE processing". Is there any way to verify this is an accurate statement? I don't see that documented in the manual.

Tom Dankowski verified this, for most of us that is gospel and we don't question it.
I have found some of the best and most useful things I have learned and added to my skill set were never printed in any manual for most brands...Fisher especially.

There is way more advice and knowledge in the collective experiences of the members of these forums than they could ever hope to put down in any manual.

 

[TheHunterGT]

F75+...indoors...purposefully giving it EMI through wifi routers, fans, TV's, LED desk lamps (that send many detectors bonkers)....should still hit in the 10-inch range.

I stop listening when people don't air test VLFs. It should be the first thing you do after getting a new VLF detector...or checking for silent EMI at a dig location....as silent EMI is a huge depth killer most don't realize is even there.

Buying a detector because another guy gets 12 inches in his fluffy soil clear across the country...now THAT is ridiculous logic. Seeing him air test one and getting similar results where I live...a no brainer.

Forget the soil test for now....and make sure it is even functioning correctly.

Do a factory reset...go 99 sens...1 disc...DE...1 tone. If not in the 10-inch range on an air test...send it back.

 

[TheEquinoxHunter]

It should air test 6inches no matter the program or sens, Something is wrong.

 

[GrantT]

Thanks for the advice all...away from home at the moment, but will follow up ASAP.

 

[GrantT]

Do a factory reset...go 99 sens...1 disc...DE...1 tone. If not in the 10-inch range on an air test...send it back.

Thanks....was playing around this morning and I guess WHAT object to use in the air test at 10"? A silver dime, a quarter, a chunk of iron?

 

[Loco-Digger]

My F75LTD is 2-3 inches off of actual depth when I pinpoint coins. If the screen shows 8 inches, the target is normally between 5 and 6 inches deep. I attribute this to the the coil being 2-3" above the soil due to the length of the grass/weeds that I am swinging over.

 

[HighVDI]

Thanks....was playing around this morning and I guess WHAT object to use in the air test at 10"? A silver dime, a quarter, a chunk of iron?

Clad dime

 

[GrantT]

OK. So was able to get out this morning and set up the detector on a plastic garbage can and set up a wooden measuring post. I am *just* able to hear a weak signal with a dime at 10". The odd little signal at 11". Does that sound like the F75 is working as expected (at least for an air test)?

That is with Sens: 99, Disc: 0, Notch: 1, Prog: DE

Pretty well the same performance in All Metal/Motion as well.

Bottle caps, pull tabs scream out loudly at 12-13".

 

[TheHunterGT]

Looks good to me. Any loss of depth during actual hunts will be due to site specific mineralization and EMI (silent and audible). Happy hunting and best of luck.

 

[HighVDI]

Good to go!