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Date Posted: 18:47:05 08/03/02 Sat
Author: Reg
Subject: Re: Air tests vs. in-ground tests
In reply to: James McCulloch 's message, "Air tests vs. in-ground tests" on 08:38:09 08/02/02 Fri

Hi Jim,

Your testing is interesting to say the least.

Several years ago, I experimented with using the disc mode and modified a Tesoro Lobo such that it would come close to the measurements you mentioned on the 1 grain using the disc mode. However, I was using about a 2 grain nugget at the time.

Unfortunately, two problems were encountered between air tests and real world conditions. One was the ever present "hotrock". If a magnetite hotrock was neaby, the disc mode sensitivity was severely hampered. If a person slowed down the sweep speed, it would help, but if the nugget was right next to or under the rock, the disc mode wouldn't see the nugget.

The second problem was actual burial tests indicated that the very small nuggets "shifted" down into the iron range, so they were then ignored at any depth below the surface. This shifting was a function of the ground conditions meaning some areas the shifting was minimal, but other areas, it was severe.

I overcame part of the problem by modifying the x channel (disc channel) by biasing on the comparator slightly. This would allow the small nuget to be seen if only the R channel (all metal channel) saw the nugget. Surprisingly, this technique didn't cause any significant iron objects to be seen as good targets but did allow the smaller nuggets to be seen as good targets in bad ground.

Unfortunately, the hotrock problem still remained.

I would be interested in your results using the two machines you mentioned subjecting different small nugget sizes to both hotrocks and ground samples.

Reg

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