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Measurements for GP Extreme 1800 coil?

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  • #16
    That seems kind of strange that one coil would do both when apparently the tx and rx circuits are split and it should be possible to do a separate rx coil. So for a mono are you suggesting that pins 2 and 3/4 are then tied together at the coil side?

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    • #17
      Hi Barry,

      Yes that is correct pins 2,3&4 are all bridged on the coil plug side for a mono coil. I guess you could build a coil arrangement with separate receive coils bu tyou would want to be mindfull of the voltages that the rx fets were going to see and not to go over their avalanche/self destruction voltage. As it is your dd coil receives from the tx coil as well. You have 2 preamps, one for the DD/rx coil and one for the tx/mono coil. When you set the detector to "N" you receive only from the dd preamp, when you set it to "E" you receive from both tx and DD coil.

      When you have a mono coil on set the switch to "E". In this position it receives from the tx coil with both preamps which reduces noise a little. You can run a mono coil in the "N" position and receive through just one preamp, but why would you??

      Cheers Mick

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      • #18
        When the switch is set for E I thought the targeting was offset because only one rx coil was being used - thanks for setting me straight.
        Btw, I never did get to Arizona. I'm presently in Fort Bragg,CA. Met mike and Randy that are forum members and find amazing stuff in the logging camps etc. here. Alas, I just brought the surf pi and a survey locator with magnetometer - hoped to find meteorites in Coloma CA - didn't work out very well, lot's of hot rocks under the grass.

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        • #19
          I think it will be helpful to post a block diagram of both DD and mono coil/preamp/tx driver options for ML detectors. I'm wondering about some other configurations now and whether they are worth trying - but I don't want to risk damaging the detector.

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          • #20
            Over the last year I bought several 11" coils (not sure if mono or DD so if cheap I just bought it), a 14" mono, and 2 - 18" mono's. I also bought a GB2 and GMT. Today I took the day off as it was a special opportunity to work the Sleepy Bear claims at Randsburg, CA. I also brought my test nugget, which is about 5mm in diameter and fairly thin. The GB2 and GMT detected it just fine but the GP Extreme didn't make a warble at all. I tried all the coils and settings. It detects iron, bullets, cans, and coins just fine - goes very deep. I scanned the internet and see some others have Extremes that seem to work (http://www.youtube.com/watch?v=F1dO-sWYEBU) and others that need larger targets. Is there a tweak or is this the best this detector can do?

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            • #21
              No need to comment on this one. I did more research and talked to a Minelab dealer as well as weighed my nugget (.23g).
              An 8" mono, 10"x5" mono, or 6" mono should pick it up - but I don't have access to one to try so I'll have to build one.
              I guess this result has to be considered when building coils for the surf PI as well. All the effort spent to make a "fast" 10" coil but it still will have a minimum size gold target that has to be determined by trial and comparison.

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              • #22
                Originally posted by bklein View Post
                Over the last year I bought several 11" coils (not sure if mono or DD so if cheap I just bought it), a 14" mono, and 2 - 18" mono's.
                Turns out both my 18" mono's are DD's. RRRRrrrrrr.
                I need to make my own as deals on ebay are too far and few between.
                Should there be a damping resistor in the coil housing on a mono (is such a resistor on RX of DD)?

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