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A return to SATisfied

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Anonymous

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Tony never really got his overview of the SAT control and I had three e-mails re its use. One backing me,one saying minimum setting gives a definate performance increase and Coco in France saying it makes no depth difference whatever the setting (he would consider it not wired in if the audio was not sharpened up!)
John CT e-mailed me some time back re his Beachscan that had also been modified with shielding, resistor in the pre-amp and delay reduced to 15us. He concluded that the one mod that had not paid off was the addition of SAT. He thought that it might help the goldhunter but not him in his search for rings.
Thought I better get back down the beach and see how much depth I am losing at the one o'clock position compared to minimum. Dropped a few rings on strings into the liquid sand and found....no gain with the minimum setting as long as (if SAT is increased) the threshold is increased slightly to allow for the fractionally lower audio.
 
S.A.T., <STRONG>S</STRONG>elf <STRONG>A</STRONG>djusting <STRONG>T</STRONG>hreshold. This has been in use in metal detector circuits for a long time, and adjustable. What the SAT does is to maintain a set threshold adjustment, by continuing to re-set the threshold circuit automatically. SAT also makes it the reason why we have to keep the coil in motion in order to detect a target. No SAT, non motion mode has been around since detectors, but it requires a constant manual tuning of the unit.
Eric installed the "adjustable" SAT, due to request from users to be able to adjust the circuit re-set time for different ground conditions, not as a depth control.
On deep faint targets that are on the outer fringes of detection, if you were to increase the SAT speed, the detector would tune out the target because of it
 
This is also modified by the speed at which you sweep the coil. Sweeping slow with a fast SAT speed will lose depth on marginal targets. Maybe with the faster and sharper response that the fastest SAT speed gives, some users unconsciously sweep faster, thereby maintaining the depth.
Eric.
 
I work saltwater beaches in California. We have much black sand here. When I am on the wet beach below the high tide line, many times the black sand is in narrow bands. I must turn the SAT as fast as possible AND slow my sweep speed a little to partially eliminate the constant changes in background. When on the dry sand, the black sand is not a problem and I can sweep much faster and set the SAT much slower. Not as slow as possible since there is also a lot of electrical/radio interference here also.
 
I did do my testing on wet black sand beaches and,as I still favour my old XLT on land with its slightly faster than the norm sweep speed I probably fitted in with Eric's suggestion that I would be using quite a fast sweep.
Dale has similar conditions by the sound of it but it is interesting that he ups the SAT and slows down his sweep which is the reverse of Erics suggestion.
I suppose the minerals/amount of ferrous present must be the variable and we must ensure that upon finding a weak target at each site a few seconds is spent checking the SAT /sweep speed are really optimised.
 
If I understand what Mr. Bill and Eric are saying. Matching your sweep speed to the SAT speed should give you the most stable threshold as well as the most sensitivity to deep targets. As far as the black sand and black sand stringers (we have them on the Southern NJ Beaches too <IMG SRC="/forums/images/frown.gif" BORDER=0 ALT=":("> If you set the Pulse Delay a bit faster I would think that the black sand should be eliminated as it's eddy currents should dissipate quickly. Possibly a Pulse Delay setting of 15us may eliminate them or reduce them substantially while still allowing the detection of small gold targets. Just my take on it.
HH
Beachcomber
 
He may be experiencing a little more unevenness than norm. His unit is a 7uS. unit that I had for testing before we came out with the Goldquest SS. If he
 
HI Beachcomber,
I have pushed the limits on my pseudo Goldquest down to the 7 usec range during my experimentation but settled on the 10 usec also. The reason is twofold.
First, I really didn't see much of an improvement in size of gold detected at the lower setting when compared to the 10 usec setup but the ground signal increased. Second, setup of a mono coil is tough enough at 10 usec, let alone trying to get one to work at 7 usec. Eveything becomes extremely critical even at the 10 usec range.
Now, there was an improvement going from 15 usec to 10 usec which is the change from the original Beachscan to the Goldquest SS. The improvement when I made this change was worth it. I didn't feel the same way when I tried the shorter delay of 7 to 8 usec.
One big advantage I see in having the ability to adjust the delay down to 10 usec is there is a slightly greater range one can set the delay to minimize noise without losing small gold.
Just my thoughts on the subject.
Reg
 
I suspected it would be very hard to get the machine down to 7us! I already knew that it had been hard it had been to get to 10us. At some point in any design you reach a point of diminishing returns. The 7us delay may be that point.....let alone being able to reliably mass produce a unit where the final tuning and adjustment would be as critical as it would be on a 7us Pulse Delay PI.
HH
Beachcomber
 
Hi Jeff,
No, as Bill says, this was the field test unit for the Goldquest. It was decided that 10uS gave the best compromise between high sensitivity and the minimum of production problems. The coil and damping get ever more critical as the sample pulse delay is shortened.
Eric.
 
When I am in the wet sand I normally run around 15us or so. Any shorter delay gives to much chatter in the threshold. I have fount a very thin gold chain (about 1/16 in dia and 18 in long) This was strung out with the shallow end about 3 in deep and the other end probably 6 or 7 in deep. Works real good in dry sand however!
 
I used a White's PI for several years. I was taught to sweep fast with that machine and that carries over to today. Also, with that machine I found out that most of the time I used the fastest delay the machine had until I hit heavy black sand. Then, I would have to go to a much longer delay. Penetration suffered but at least I could still find items. This is also why I slow my search speed.
 
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