BigSkyGuy Posted January 5, 2019 Share Posted January 5, 2019 Hello all, I am gearing up for a relic hunting trip in the southeast US. I have permission at a nice CW camp, that I used to hunt over 30 years ago with my White's 6db and 5000-D. I think this would be a great place to take the GPX-5000 (nice red dirt). However, a power line runs right through the middle of the camp. This was a minor issue for my White's vlfs, but may be a bigger issue for a PI. I have two AI coils, an 11" and a 14" inch which work great for the EMI which typically occurs around, or in, houses. However, I have never tried them beneath or near a power line. I want to make sure I have a number of options if the AI's do not work. I have read the manual pretty thoroughly and searched the forums and came up with a list of methods to minimize EMI (see Table below). One of the techniques was mentioned by Jonathan Porter in a Treasure Talk article on the GPZ-7000 (link below). He mentioned that "Bogene's Settings" are effective for the GPZ-7000 and have been used in the past for the GPX line for reducing EMI and ground noise. https://www.minelab.com/treasure-talk/using-the-gpz-7000-in-high-emi-conditions-and-audio-smoothing After a bit of searching, I came up with the original thread (link below), which dates back to 2008 and was originally applied using the GPX-4000 and GPX-4500. The method consists of turning down the threshold (until there is no "hum") and turning up the gain and/or stabilizer. http://www.finders.com.au/forum/viewtopic.php?t=3442&postdays=0&postorder=asc&start=0 The technique appears to have been originally developed for very hot ground in Australia, but Jonathan Porter indicates that it can be used for reducing EMI, at least for the GPZ-7000. My question is, has anyone used this method on the GPX-5000 for reducing EMI, and if so how effective was it and what were the disadvantages if any? If this topic has already been covered, I apologize in advance. Thank you! Adjustment Disadvantage of Using Use AI Coil Loss of depth compared to same size DD Use smaller DD coil Loss of depth Decrease gain Loss of depth Use Sens Extra, Normal, or Smooth timing Loss of depth (compared to Sharp timing) Decrease motion medium → slow → very slow Must swing slower Use “Quiet” Audio Type May miss faint signals Decrease stabilizer setting May miss faint signals Lower threshold and raise gain/stabilizer (i.e. Bogene’s Settings) Unknown if this will work for GPX-5000 or how effective it is for EMI. Use Cancel CoilRX setting Inability to discriminate, loss of depth Link to comment Share on other sites More sharing options...
Steve Herschbach Posted January 5, 2019 Share Posted January 5, 2019 Link to comment Share on other sites More sharing options...
fredmason Posted January 5, 2019 Share Posted January 5, 2019 I would use a large DD and Cancel mode...but, if you want iron-discriminate, probably not an option. D never worked very well anyway... I never used the A. I. coils, so no opinion on that. good luck fred Link to comment Share on other sites More sharing options...
PhaseTech Posted January 7, 2019 Share Posted January 7, 2019 Put simply, the AI's or DD coil in Cancel is your best defence against high voltage power lines or electric fences. 2 Link to comment Share on other sites More sharing options...
GoldEn Posted January 8, 2019 Share Posted January 8, 2019 Hi BigSkyGuy, Just me preparing for that trip and thinking loud: As its relic hunting if any possibilities I take treasure hunting detector. Its great opportunity to go after many years to a site with potential so I would try to make most of it. I used Gpx5000 many years in Australia for gold detecting.I tried Bogene settings with and without power lines close.Didnt have much success.Did detect close to power lines and had lot of problems with EMI.even 30-50 meters far it was hard or near impossible to detect.One thing which I noticed helped was to put frequency very low.So try to do manually lower until you can detect or get to the level you can put up with it. Putting in cancel practically you dont have much depth and target has to be quite large.As Fred suggested DD coils are one of better options. I used 10x5 DD coil and it was great but smaller coil smaller area to cover and shallow. Hope you have fun. If you are treasure hunter buy or try equinox and you will be a very happy treaure hunter. Just my personal preference (I have 2 of them). Wish you luck. Stay safe and dig everything. GoldEN 2 Link to comment Share on other sites More sharing options...
BigSkyGuy Posted January 8, 2019 Author Share Posted January 8, 2019 Thanks for the advice. I think I will take the 11" DD, 5x10" DD, and 11" AI. I also have an Equinox 800 to take. Link to comment Share on other sites More sharing options...
PhaseTech Posted January 8, 2019 Share Posted January 8, 2019 If using a DD coil in Cancel, you can often tweak up the machine to get back some of the depth loss. Depending on ground conditions of course. For coin/button sized targets, I'd use Normal timing, and possibly even Sharp depending on the ground. 1 Link to comment Share on other sites More sharing options...
Daniel Tn Posted January 9, 2019 Share Posted January 9, 2019 Sounds like similar conditions to a civil war camp I hunt too. A high tension powerline runs right thru it. I have not found a magic setting on the GPX to allow one to hunt there. I have tried small coils, AI coil (11"), Cancel mode, and various other tricks. I tried hunting thru the warbling and motorboating and did pull some bullets and burnside casings out of my camp but nothing deep. I hunted it with a TDI and could get closer to the lines but not under them. I hunted the edges really well though. In my case I haven't had a VLF that ran smooth there either but the DST mode F75 in all metal seemed to work decent and was deeper than the GPX running throttled back. Have not had an Equinox on that camp yet but have ran into emi with mine in other areas so I figure it will be hard to hunt there with it too. Gonna give it a whirl though this week. Link to comment Share on other sites More sharing options...
BigSkyGuy Posted January 15, 2019 Author Share Posted January 15, 2019 On 1/9/2019 at 12:07 AM, Daniel Tn said: Sounds like similar conditions to a civil war camp I hunt too. A high tension powerline runs right thru it. I have not found a magic setting on the GPX to allow one to hunt there. I have tried small coils, AI coil (11"), Cancel mode, and various other tricks. I tried hunting thru the warbling and motorboating and did pull some bullets and burnside casings out of my camp but nothing deep. I hunted it with a TDI and could get closer to the lines but not under them. I hunted the edges really well though. In my case I haven't had a VLF that ran smooth there either but the DST mode F75 in all metal seemed to work decent and was deeper than the GPX running throttled back. Have not had an Equinox on that camp yet but have ran into emi with mine in other areas so I figure it will be hard to hunt there with it too. Gonna give it a whirl though this week. I will have the EQ800 with me as well, so I will have some options. I will let you all know what I come up with. Thanks Link to comment Share on other sites More sharing options...
PhaseTech Posted January 16, 2019 Share Posted January 16, 2019 On 1/8/2019 at 6:55 PM, phrunt said: Do you think something like an Equinox or other HF VLF will perform better than a GPX when in Cancel with a DD under power lines? The VLF can handle power lines much better but would it be comparable in depth to the PI in that scenario? I can run my Gold Bug Pro and Gold Monster 1000 maxed out under power lines no problems at all. I still haven't found a working viable solution for me to use my GPX under power lines that I'm happy with, the DD didn't solve the problem for me, Cancel was OK but I felt the detector was gutless when in Cancel and thought perhaps I'd be better off swinging something else instead but didn't want to have to walk back to the car to get it ? The GM isn't scared of power lines even in manual 10. The Nox copes pretty well with high voltage too, but you have to adjust the settings accordingly, usually just disabling multi IQ and going to 40khz is all it takes. I'd love to find a solution to my GPX and high voltage power lines but so far I've had no luck, the DD did improve things but not as much as I'd like, my smallest DD is 11", so perhaps I need smaller? If it's bad ground, then a VLF or Multi will never match a PI for depth, even if using a DD in Cancel. But in mild ground, I reckon things could get interestingly close, especially on very small gold. Yes, most high freg VLFs perform very well under high voltage lines, Monster, Gold Kruzer, Eureka in 60 kHz, and others. And you are right with the Nox, you will get better stability in one of the single freq options compared to Multi. And with your last question, if you didn't have luck with an 11" DD in cancel, I don't think going to a smaller DD will be the answer. Going down to say an 8" DD, such as the Detech may reduce noise by a small percentage, but you will just further reduce depth. I have used a 10x5" Commander DD in cancel, and it purred like a kitten, but with only a 2.5" width winding, you can imaging I wasn't about to dig any deep targets ? But for the GP series that are not equipped with any of the smooth timings, but do have cancel modes, those two small DD's are great to have in the kit! Link to comment Share on other sites More sharing options...
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