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Date Posted: 15:37:53 08/23/02 Fri
Author: Reg
Subject: Re: Updating a TR
In reply to: Tom_in_Salinas_CA 's message, "Question for you techies" on 12:50:22 08/23/02 Fri

Hi Tom,

Your post is interesting and does pose a couple of good questions. Could technology bring the old TR design up to better standards? Yes, but I suspect many people would be disappointed. Too many people have become accustomed to ground balancing and fancy discrimination to go back to the old ways.

The old TR's, which operated at a much higher frequency, basically amplified a change in the signal amplitude from the receive coil for detection. Fortunately, one of the byproducts of the DD coil was it would ignore nails, yet detect coins below the nails. I am not really sure as to why the coil works the way it does, but the results are clear. Unfortunately, the ground also produces an amplitude variation so the ground does pose a problem.

Now, the basic improvements would most likely be in the autotune feature as mentioned by Steve. If the autotune were fast enough by maybe using the motion filter speeds, then the ground response could be minimized, but there would still be places where it would be difficult to use the detector.

VLF's operate at a much lower fequency, not so much for deeper penetration, but for target separation and maximum signal strength back from the target in question. Since coin hunting was the primary purpose for detectors, the frequency selected was aimed at providing the strongest signal from coins. The 6Khz range detectors were designed that way.

Some time later, manufacturers began changing frequencies. When I asked the question as to why, Jack Gifford of Tesoro said it was basically to get away from the frequency used by other detectors. This made it possible for two detectors to work very closely to each other.

I recently posed the question to George Payne about ground signal loss that might occur at the old TR frequency of 100Khz. Since he was in the middle of a project he didn't have time to run through the calculations, but did mention from what he could remember about the old TR's the actual depth loss probably wouldn't be that great.

To add credance to that, we should remember the Goldbug 2 operates at 71Khz now and I have never really seen any depth loss.

What would be lost at the higher frequencies would be the target separation, meaning it would be very diffult to determine the difference between, lets say, a pull tab and a coin if the motion technology were to be used..

Now, what might be interesting would be a dual designed detector operating at 100Khz. By this I mean one could select the old TR amplitude form of detection or be able to select the synchonous sampling technique with motion discrimination used on VLF's today.

On the plus side, a detector designed this way should see an enhancement to very small gold nuggets. Also, it is quite possible the iron response wouldn't be as great as it is on the VLF's. However, without experimenting, I can't say for sure about the iron.

Reg

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