Air test on Explorer

[Tom NW MI]

Just curious if anyone can give me some insight on why Explorer users do not get good air test results yet they seem do be one of the deeper machines on coins? All I have seen posted on the subject is that they "need to see the ground matrix" to get good depth. Is this correct?
Thanks
Tom

[Brian]

Re: Air test on Explorer

The reason given by Minelab when the Sovereign came out was that auto sensitivity would set to a mid power setting if no ground mineralisation was detected. Thus air tests should always be done with with the knob clicked over into manual (maximum) sensitivity. I don't really see why this should apply to the Explorer or the XLT though they do both seem to like compressed ground rather than a freshly ploughed fluffy dry soil.
I have test beds of 22 and 15 years (high and low mineralisation) with targets ranging from gold through silver and copper to ringpulls and cannot say that depth is improved in ground with any VLF machine over air tests its just that some machines lose a lot and others only a little. Poor pinpointing is the reason why fantastic depths are claimed. Miss the target,dig to 2 or 3 feet,the side falls in and we have another super depth machine.
Before halo effect is mentioned, if a coins got a good halo its not a collectable coin and if its got a good patina its become at one with the soil and is no longer reacting plus ploughing,general earth movement and worm action ensures a target enhancing halo is not formed. Have a well decayed coin in damp/wet soil and you get a slight electrical current as the soil acids attack the metal and detectable depth increases slightly. This type of target can move around leaving its halo behind and continues to be more detectable than the norm as long as it remains damp enough for the chemical action to continue.

[GaryQ]

Re: Air test on Explorer

Brian,

Well said and spot on : Poor pinpointing is the reason why fantastic depths are claimed. Miss the target,dig to 2 or 3 feet,the side falls in and we have another super depth machine.

Also VLF's as you said cannot improve their depth In-Ground over its Air-Test.

However Mr Candy (Minelabs SD inventer)said his SD-PI Air-Test was for the first time a good indication of its In-Ground depth.

[Reg]

Re: Air test on Explorer

Hi Brian,

I like your comment about some detectors like compressed ground more than plowed ground. Many people don't notice that plowed ground can cause depth loss and incorrect TID.

The big reason for this has to do with how VLF's work. The motion filters are designed to minimize slow changing ground mineralization which is the norm when the ground is relatively flat. However, when plowed, the ground signal can be much greater due to the sudden surface changes. Thus the ground response can interfer with the target signal.

The use of a DD type coil can help in this regards.

Two other things that can help when using a VLF over plowed ground are to slow the sweep speed down and search with the coil a little higher above the ground.

Reg