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green

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  1. Time constants for some targets I have. Target frequency=160kHz/us TC, 2us TC=80kHz. Expected time constants for gold chain? lead shot, gold nuggets and gold chain
  2. Any thoughts, why some GPX 6000's can detect #9 lead shot and others not? What detection distance are you getting for #9 lead shot with your GPX 6000?
  3. Interesting topic. I sent some targets to someone that has 6000 and 7000 detectors. Targets included #4, #6, #8 and #9 lead shot. Both detectors could detect #4 and #6 shot not #8 or #9 shot. Guessing coil size might be some of the reason. Is being able to detect #9 shot important, if so at what distance?
  4. Hi Chet Thanks. Know wondering if a length of copper wire might be a better target to compare detectors. For GB_Amateur, #9 lead shot is about .7us
  5. Hi Gerry, interesting topic. I've been trying to make a PI detector detect #9 lead shot. Wondering how much harder your nuggets are to detect. Have you compared #9 lead shot with some of your nuggets? Maybe a single piece and another with 16 pieces on some masking tape folded over making a square 4x4 pieces? A piece of #9 lead shot has a time constant less than .7us, 16 pieces should have the same time constant with 16 times the signal.
  6. I'm probably wrong, wouldn't be the first time. Detection is S/N. Noise is random, don't know if algorithm can reduce something that keeps changing.
  7. Compared some nuggets and lead shot from shotgun shells. Used a PI circuit, 3.5us delay with a Rx coil about 5 1/2 inch diameter. Appears 4, 6 and 8 shot are similar to the 8mesh nuggets. If I were to try to find small gold nuggets what detection distance for the lead shot should I want? Larger coil would improve detection distance for the larger nuggets.
  8. Time constant chart for lead shot. Signal 1 decade less for every 2.3 times target time constant. #9 shot less than 1/4000 of start signal at 7us delay.
  9. Try a standard Bic plastic ball point pen medium tip - small brass tip with 1mm tungsten carbide ball. Steve Herschbach has used it for years as a standard for testing gold detectors - also easy to stick in the sand and hard to lose. - and, of course available everywhere.Google Steve Herschbach bic pen and read what he has to say about it. It apparently behaves a very low conductive target. It presents in interesting test of the cut-off setting of a detector with iron discrimination - Might ve interesting for MantaHere’s the results one guy got with his nugget detector on various targets (the POINT - lol - is to show how tough a target the pen tip is....)”Bic Pen-3/4" 1/2 Grain (not gram) nugget 1" 1.3 gram nugget 5" . One tenth oz gold coin 8 1/2".. from Finds Technology Forum When I saw this posted the first time I tested some ball point pens from motels I had stayed at. Didn't have a Bic. Pen A(3.5us time constant) pen B(2.2us time constant) pen C(.65us time constant). Saw reply again the other day. Found Dollar General had 10 BiC Round Stic medium pens for a dollar, 1mm tungsten carbide ball. BiC(2.1us time constant). Charts a little less than a 4grain nugget I have. Wondering why test above has BiC pen closer to 1/2grain nugget than a 4grain nugget. Maybe missing I'm something. Thought I would go to the source to ask. The time constant of ball point pens can vary a lot, wondering if the one I used is the same as used in the test above. Does look like a BiC Round Stic medium tip would make a good test target.
  10. If the ID is close to a nickel, my guess is Titanium 6AL-4V
  11. Trying to learn something. Didn't have an idea how fast smaller nugget signal decayed. Have asked before in another forum and always got the answer, to much variation. Wanted to know how small a nugget a good PI detector could detect to get some for testing. I made a PI circuit. Tx coil, Rx coil, control circuit, amplifier looking at Rx and log amplifier looking at amplifier out. Record log amplifier out vs time and chart. Most targets with a time constant<10usec decay straight line on a linear log chart. Loose 63% of signal every time constant, loose 90%(decade on chart)) every 2.3 time constants, loose 50% every 3 small divisions on chart. A eight inch coil could loose 3 to 4 inch detection distance for every decade lose in signal. The shorter the time constant the sooner the need to sample. Probably need a smaller coil to get a good chart for the 8mesh nuggets, data below the 0 line(1% 0f full scale amplifier out)starts to be effected by noise when charting. Added a 1 and 2usec time constant decay line on chart to compare target decay with, most nuggets decay with a slope between the two lines.
  12. Charted the nuggets. Looks like most of the decay TC's between 1 and 2 usec. Nuggets look a little larger than I was expecting, probably couldn't chart much smaller nuggets with my tester. Receive signal getting in the noise. Thanks again for suggesting 8mesh
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