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Offline allanwjacksonTopic starter
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« on: September 28, 2010, 01:26:15 am »
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I have a Garrett Master-Hunter Detector.  When I bury a 10mm Diam. silver coin to a depth of 150mm, my detector sometimes recognises the target and sometimes doesn't acknowledge it.  The problem is, if I scrub the coil on the ground I get a crisp response from the detector every time.  My manual says to sweep at a height of 25mm. This means that sometimes I would miss a target.  Can anyone explain why scrubbing makes such a difference, I don't think 25mm should make much of a difference to the target response, apparently it does.

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Offline GoldDigger1950
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« Reply #1 on: September 28, 2010, 03:52:07 pm »
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Presuming you have introduced yourself elsewhere, I'll add my welcome here. Welcome from Australia!

Scrubbing is a technique that can increase the signal strength received by the receiver circuitry. The transmit signal isn't affected as such because it is so strong but the very weak signals that come from the metal can be greatly enhanced by scrubbing.

Here's why. The transmit signal is strong. It has to be to create a field in the coil that will penetrate the ground. That signal and field energize the metal targets in the ground and cause a tiny electric current to flow in the metal. Because the current flows, a small field is built up in some manner in the target metal. For ferrous targets, iron and steel, the small field, known as an eddy current, is aligned internal to the metal. In non ferrous, like gold and silver, it is on the surface of the metal.

Your receiver coil has to pick up those tiny fields from the target so as you can imagine, the coil and receiver must be very sensitive. Within the soil, those fields are carried along in a moisture and mineral laden environment which actually helps it along. The air is not a good conductor at all so that seemingly small gap of 25mm has a big effect on things. Scrubbing puts the receiver coil in near contact with the soil, enhancing the sensitivity. The down side is that you wear out the plastic if you keep doing it. I recommend a coil cover.

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« Last Edit: September 28, 2010, 07:59:24 pm by GoldDigger1950 » 		Logged
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« Reply #2 on: September 28, 2010, 04:05:16 pm »
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My Take on this one is you have not Ground Balanced correctly.

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Offline GoldDigger1950
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« Reply #3 on: September 28, 2010, 04:44:04 pm »
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Homefire, it could be the case but even with perfect ground balancing, the scrubbing technique will increase target response. Not depth. Just target response.

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Offline allanwjacksonTopic starter
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« Reply #4 on: September 28, 2010, 06:33:07 pm »
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Thank You for your comment.
Very informative, and a common-sense approach.  You have explained exactly what I needed to know.  I thought I may have been tuning incorrectly.  If I had stopped and thought about it, I should have drawn the same conclusion as your comment.

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Offline Paul A
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« Reply #5 on: September 29, 2010, 02:35:31 am »
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Was watching a guy on the beach a couple of months back.
Don't know what kind of detector it was (didn't get close enough and didn't want to the way he was cussing)
But he was swinging the coil at least 6 inches above the sand at 100mph!
Needless to say........ he wasn't finding much!  No no!


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Offline GoldDigger1950
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« Reply #6 on: September 29, 2010, 02:41:09 am »
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Quote:Posted by Paul A
Was watching a guy on the beach a couple of months back.
Don't know what kind of detector it was (didn't get close enough and didn't want to the way he was cussing)
But he was swinging the coil at least 6 inches above the sand at 100mph!
Needless to say........ he wasn't finding much!  No no!


I saw that same guy here in Australia! That same day, I came home with over $100.00 in modern coinage and a few jewelry items. He stopped by and showed me 40c for an hour's work and complained about how bad things were. I guess I cleaned out the entire beach that day. No wonder I was so tired.

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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.
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