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Date Posted: 12:07:23 08/15/02 Thu
Author: Ralph
Subject: I think you're on the right track......
In reply to: Reg 's message, "Nugget hunting using discrimination" on 00:30:01 08/14/02 Wed

Hi Reg,

I think you're on the right track in your comments about contacting Dave Johnson concerning this. I don't know that he will divulge the "technical aspects" involved, but considering that the GB-II, X-5, and MXT are "out of the same litter" so to speak, I wouldn't be surprised to see something in the circuitry that carries over between all three models. The gold / ferrous separation is excellent on all of these machines. One of the demonstrations with the early X-5 prototypes that really astonished alot of folks was that you could discriminate out a large rusty square nail to a very broken "clicking" audio response (something similar to the Fisher "X" units) and then place the nail THROUGH the middle of a small womens karat gold ring and get a strong, "good" signal on the ring. I have my suspicions though that it is more than just the ring creating the good signal, and more likely a combination of the two. I'm not quite sure of the specifics where the circuitry is concerned, but this seems to happen (with the X-5 at least) at a very precise point on the discrimination control, just at the fringe of ferrous / gold signal separation. A bit too far in either direction, and you either begin to pick up the iron or lose the gold. This would be a great application for a vernier type pot to get that "just right" precision on the discrimination control.

From specific experimenting I've done on the X-5 with small nuggets being detectable in close proximity to hot rocks, it still seems to be a matter of "depends on the size and signal strength of the hot rock and the nugget", only the detectability of nuggets next to hot rocks is much more pronounced than with any other VLF/IB machine I've used in discriminate mode. If the hot rock has a strong enough signal (stronger than that of the nugget) it is still masked in most instances. But there is something there permitting detection of smaller nuggets near stronger hot rocks than is the norm for VLFs. With the X-5, operating in beach mode also seems to negate the hot rocks to a greater extent while still "seeing" the smaller nuggets.

Considering the 19kHz operating frequency of the X-5 vs. the significantly higher frequency of the GB-II, I think there is alot more to it than just the frequency. Alot may also have to do with the +- component tolerances used in
the X-5 as compared to those of most detectors, something along the lines of +-5% in comparison to +-2% or 3%. Elimination of internal noise problems just might be allowing for the closer precision of the discrimination settings.

Another thing I've noticed with both the MXT and X-5 is that they share the characteristic of being equally sensitive to both high end (silver) and lower end (nickel and karat gold) targets, where most discriminators are weighted more toward one end of the conductivity scale or the other. These machines don't seem to lose anything on either end as do some of the Tesoro machines for instance, which tend to have excellent sensitivity to lower and mid range conductivity, but lack some on higher end silver coins at depth.

Interesting topic.......

Ralph

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