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Tried the GP Extreme at the Beach


I tried my GP Extreme at the beach this weekend. First I was trying the Platypus coil and it would not detect a nickel so I had to switch to a Commander Mono coil. Probably 11".
I'm suspecting the female pins of the coil connection have contacts that are too wide apart for the male pins. Have to check it out.
Anyway, what intrigued me was that the Commander Mono coil ignored foil. Even big foil. It detected targets well, there just were not many of them there. It was fine in the wet sand. It took some getting used to to hear the tone whoop with the coil swing though. I'm guessing that's normal - sure could be nicer if it was just a threshold tone. My Equinox 800 would have been sounding off on all the foil bits, driving me crazy. I switched to my CTX and it was much more pleasant to use - lighter, quieter, and seemed to pick up a bit more targets but that may be because I was working a different part of the beach than earlier.
I guess things were too sanded in for the GP Extreme to make much difference. It did find very small things but the CTX is good at that too - just not the greatest at gold chains perhaps.
Let me know if this all seems about right for the GP Extreme.


New member
Ignoring foil is a feature of PI machines with longer minimum pulse delays. The pulse is cut off and after a delay, the target signal is sampled. If the pulse delay is greater than that amount of time required for the signal from the target to decay below detectability, the target signal will be gone by the time the sample is taken.


I thought that it is critical to have a fast pulse response time to detect small gold. So you are saying foil is even a shorter delay required to see?
Is this inherent in the GP because of a setting I did? I would think to see small gold Id have to make the sacrifice of seeing the foil.
Or is something wrong in the front end of the machine or coil, killing fast response time perhaps?

Nice to have depth and miss the foil. Does the surf pi do the same if it has a pulse delay control? Have one never realized it if it does.


New member
It’s a factor of how all PI detectors work. They pulse, cut off the pulse quickly and then pause before they sample target response. During this “pulse delay” fast decaying signals reach very low levels or decay entirely. Signals which decay more slowly are still there when the detector - after the designed pulse delay - samples the return signal.

The fastest I have ever heard of a prototype detector sampling after cut-off was about 6.5 microseconds. Seawater’s signal is not detected after the delay exceeds at least 6 μsec. Your GP is likely waiting something like 15 μsec before sampling. Most PI beach detectors are around that figure. Diving PI machines have even longer minimum pulse delays because of the sheer volume of salt water they “see”.

Thin foil as well as tiny low conductors like tiny gold jewelry are not detectable after very short pulse delays - probably 7-8 μsec.


Tried it again today at the beach. Got the Platypus coil working it seems. Must have been a spread open connector pin receptor.
It works fine in dry sand but in the wet sand it is too noisy to tolerate. It just about pegs the input but backs off so I suppose you could hear a target but it is just too much work on your brain to use. Electronics in other detectors fix this. Another possibility is a different behavior with a different coil type like a mono(?) Didn't get a chance to try.
Heavy beast. Went back to my CTX and thought is was so much easier on my brain and right arm.