I tried this iron-maskingn experiment yesterday

[ziphius]

Out of curiosity, last night I took a clad dime and piled three square nails on top of it. I was operating my F75 at a sensitivity of 60, which is mid-range for this machine. Tones were "delta pitch", which means that higher VDI readings have higher tones. Iron sounds like a fart and high conductors sound sweet. My F75 got the dime tone just fine, though the VDI was reduced from what would normally be a 73 reading to something in the low 60s. There was almost no iron tone from this mixed target. If I backed way off on the sensitivity to say 30, then the dime tone was degraded considerably and the iron tones were more dominant.

In monotone, the mixed target sounded exactly like either of the two pure targets. The chances of the mixed target sounding like mostly iron was reduced by switching to monotone. I think this is what Dankowski was getting at when he suggested operating the machine in monotone in iron-infested areas. But I think that if you can run your sensitivity high enough, the F75 just sees right through the iron. If anyone has other testing suggestions, I'd be happy to try them. - Jim

 

[19beavers]

Try putting down a "carpet of nails" say two feet square with a coin in the middle and see if the F75 will find it.

 

[Bill in Texas]

Try putting one nail about 3 inches right above the dime! In the field junk is almost always shallower than coins or jewelry. Bill in Texas

 

[iliketodigit]

Hi ziphius, have you tested what Bill has suggested ?
Even if the nail totally masks the good target I'm not too worried.
Much of the land that i detect on in the UK gets heavily ploughed so things are constantly moved up and down above and below one another.
Just means it will take some time to completely search out a field, every return visit promises the chance of new good finds.
Thanks, Mart.

 

[ziphius]

Someone on another forum noted that I had placed the nail directly on top of the dime and suggested doing a test where there was some separation between the dime and the nail. To better reflect real-world conditions. I placed the dime on the ground. Placed a thin notebook on top of the dime. Put one nail on top of the notebook. The dime is masked, except in cases where the coil is swung over the short axis of the nail. If the coil is swung over the length of the nail, the dime target cannot be heard. With an inch or two of separation (nail isn't directly over dime), then you can start to hear the dime target. But, those of us who use F75s regularly know that it has great recovery speed and the ability to separate two targets in close proximity. I'll tinker around with a bit more testing.

 

[iliketodigit]

On U Tube there is a Spanish guy doing live test with the F75 standard coil and a larger coil.
The nail is not put on top of the coin but to one side or above.
Above ( long axis ) the coin is not picked up.
To the side ( short axis ) the coin is picked up.
Likewise there is a test by "Norfolk Wolf" = Regton Metal Detectors doing various recovery tests.
A coin is placed on a board on the ground with a nail placed long axis to the side.
At about 2 inches the signal is downgraded and lost, however on 3 inches a short blip can be heard when passing across them both meaning a fast recovery time for the F75, any further apart and the good signal is gets clearer.
That short blip could well indicate a good target.
Combining your 90 degree post with this one emphasises the need to check all signals from all angles reducing the chance of missing anything.
Great thread, Thanks. Mart.

 

[ziphius]

Yeah, I've seen that Norfolk Wolf video. He does a good job with his testing and videos.

 

[daryllpugh]

The only thing is. He does'nt try it in all metal. Just disc.. In all metal you'll see a difference.

 

[ziphius]

and yes, of course, with all-metal mode, there is no masking issue. Unless you forget to recheck your hole after you pull out the undesirable target! Happy New Year everyone.