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Another audio question

A

Anonymous

Guest
I'm curious to know why my audio drifts slightly when the coil is swept in one direction only. I am using the Goldquest SS.
This happens when I'm working in the water.
The audio drift occurs only when the coil is swept "out to sea". There is no coil lift and the bottom of the sand is nice and even. When I start my return sweep towards the beach, the normal threshold returns, which for me is a just audible one.
I can only assume that this problem is due to the huge volume of water that the coil "sees" when swept in that direction. When I sweep parallel to the sea (now turning 90 degrees), the problem is gone???
 
Hi Tony,
Your assumption is correct. It is the increasing volume of water that the coil sees, as it is heading seaward, that causes the threshold to rise.
Eric.
 
Mr Bill/Eric,
It still amazes me that the detector can sense this increase in seawater towards the open ocean. The Tx field must radiate out some distance to result in the saltwater interference, because it's not bothered by the shoreline which would be some 20 metres away (gradually becoming shallower).
Sweeping parallel to the open water gives no audio drift but that's still a lot of Indian Ocean water to the left and right. I figure it's at a constant depth in these directions but a lot of salt water all the same.
I shall have to tweak the SAT just enough or adjust my search patterns.
Thanks for the feedback.
 
Hi Tony,
The Goldquest has a fast reset circuit that operates on negative going signals. As you move the coil toward the shore, the signal is progressively going negative (or less positive, if you like). Without this reset circuit the audio threshold would go negative, or become temporarily inaudible until the SAT circuit compensated. The reset circuit ensures that you never lose the threshold. When you move the coil toward deeper water, the reset circuit does not operate, otherwise you would cancel your wanted signals as well.
It is the change in ocean signal that affects the threshold. In water of constant depth, the signal will be reasonably constant an the SAT will tune it out. Most shores have a slight slope and searching at right angles to the shoreline will give a change in signal. A change also happens if there is a varying depth of water saturated sand over bedrock or impervious clay.
Eric.
 
I move around quite a bit and hunt many different beaches all over Florida and other states...I have noticed the slight threshold rise when facing the ocean on some beaches and not on others. Never thought about the slope of the beach but rather figured it was as the water gets deeper the concentration of minerals and salts compresses with the weight from the additional water pressure and weight, saltwater is 64.33 pounds per cubic foot or there about, I was thinking the weight of the water and getting closer to the next atmosphere (deeper) was somehow affecting the unit. Again this is not every beach and again never thought about the angle or slope...
Thanks,
Frank
 
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