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Date Posted: 10:15:52 08/28/02 Wed
Author: Reg
Subject: Re: PI's and small gold nuggets
In reply to: Rob-AZ 's message, "PI's and small gold nuggets" on 14:45:27 08/27/02 Tue

Hi Rob,

Great pic of some really small nuggets. It is obvious the Extreme does exceptionally well on real small nuggets.

One of the big reasons for the statement PI's are not designed for hunting small nuggets has to do with both the response of the nugget and the design of the detector.

Yes, it is possible to be able to detect the smaller nuggets like those in the pic you posted. To do so, the sample delay time has to be very short, 10 to 12 usec or less.

One problem involved in getting down to those short delays is coil design. It is tricky to get a coil to work at that short of a delay. This probably accounts for the higher costs of such coils.

It gets worse, the larger the coil, the more difficult it is to get a coil to work at the short delays.

Since PI's are normally designed to find larger and deeper objects, many manufacturers have elected to pick a longer time as their minimum delay setting. Thus, many of other PI's will fair much worse on nuggets in the 1 to 10 grain range.

However, on a larger nugget, say a pennyweight size or larger, it is quite possible two detectors, even though one may able to detect the smaller ones better, may have about the same depth capabilities.

There is also a very fine line in design when it comes to target volume which many perceive as sensitivity. Example, two detectors may detect the same deep target, but one detector may have a louder response. Is the one with the louder response really that much more sensitive? Maybe or maybe not. If we take into account that some weak signals may not be heard because one cannot distinguish the slight threshold change on the one having less gain, then the answer would be yes.

It is easy to make a weak signal louder, but at the expense of stability or smoothness of the threshold. In other words, two detectors may detect the same nugget with one giving a louder signal, but chances are, this same detector will have a much noisier threshold.

This threshold noise can be in the form of pops, chatter, or if some fancy filtering is used, a warble.

Some manufactures have elected to limit the amount of amplificaton to eliminate the excessive threshold noise whatever it may sound like.

I havn't tried an Infinium, but I suspect that is the case with this detector. Chances are, Garrett will give in and make the mods necessary to provide louder responses to smaller nuggets and really deep targets. In the meantime the owners of the Infinium will just have to live with the smoother threshold.

It is also possible that an after market amplifier might help considerably. I would be interested to hear the results from someone who has tried one on the Infinium

The use of a mono coil on the Infinium or any PI for that matter should help the small nugget response. It will not cause nuggets to be heard who's signals that have already decayed, but the mono coil should increase the volume of those that now produce a very very weak signal.

There have been some discussions indicating there are two Infiniums, one for the US and one for Australia. If that is true, it is possible the Australian model has a shorter delay. Only a side by side comparison would verify that.

Maybe one of the more influential dealers can find out from Garrett if there is a difference and what the differences are.

My assessments are based upon my own experimentation and the results I see on my Eric Foster designed PI. It is fun to experiment down to the component level and see why certain things happen. Some of the things that have come out of designing a ground balance are really quite interesting. It explains a lot about the problems of discriminating on a PI.

Reg

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