GPX Settings

[Daniel Tn]

I just recently purchased a GPX 4500. I bought Jonathan Porter's "SETA Project" dvd and got it in the other day. He does a very good job explaining the differences between the 4500 and previous machines and also demonstrates the changes per timings on real world nuggets. I like his format in doing tests like that. I am well aware that now the 4800 and 5000 are the cats meow now, but I still haven't fully learned the 4500 as of yet. So I have a few questions regarding timings and a few other items. I noticed Mr. Porter occasionally posts here so maybe he can put some feedback in here as well.

I am using the GPX for relic hunting. BUT don't think I'm hunting in low mineralized ground. I am hunting in heavy red iron bearing ground; VLF machines just don't work good here, there is too much feedback from the ground itself and it masks targets in it. I don't think it is as severe as the ground in AU but it's not exactly what you would call benign either. While the end targets may be different...the machine setup is going to be very similar. We are seeking low to mid conductive items, at depths of 6 inches to a couple of feet.

I notice in Mr. Porter's video that he uses the mono coils almost exclusively, and most of his video setup and settings were for mono coils. My first question here is, would a mono coil benefit me over the stock DD coil for more sensitivity and therefore depth? My thinking on this was that mono coils were only for low to mid mineralized ground, but Mr. Porter is using them in heavily mineralized ground with obvious good results. I only have the stock 11" DD coil. If the Mono coils would be better, then which ones should I consider? Minelab brand coils or after market coils by 3rd party companies? The reason I ask is because these coils are pretty expensive (to me). Some of the CoilTek coils are over $400 US money!

Next question is dealing with EMI. Mr. Porter touches bases with this, BUT he does a segment on setting the 4500 up to combat EMI with a mono loop coil. Would similar settings be used with a DD coil? Where I hunt, we have a lot of EMI from power lines and etc. In some cases, when a large group of us get together, there may be 100 or more PI machines running around one another. Would there be any settings I might go to, to quieten the machine down while using the stock coil? And would the settings be different for that, than for hunting around the power lines?

Next question is batteries. It seems like Minelab designed the new battery/charger/amplifier to be used as a multi purpose type deal...say for those wanting to use an external speaker or for those using headphones. Where I hunt, I have no need for an external speaker so I use headphones all the time. A replacement battery from Minelab is very expensive....are there any 3rd party batteries that you would recommend that might be lighter weight and just be good for using with headphones? Who are they are what is expected battery life time on them? I'm looking for any way to shed some ounces of weight.

 

[Jonathan Porter]

Hello Daniel, to try and answer some of your comprehensive questions. Monoloop coils will always provide a sensitivity and depth advantage over a DD coil, reason being a DD coil has two windings which cross each other down the length of the coil from front to back, the proximity of these two windings allows the coil to be used in high mineralisation as well as providing simplistic discrimination. However the trade off from going from say an 11' mono to an 11" DD is approx 30% in depth. DD coils do have pretty good sensitivity for their size because the smaller a winding (loop of wire inside the coil) the greater the amount of turns of wire to get the inductance right in the coil, more windings equals greater near coil sensitivity to small targets which goes some way in reducing the performance reduction of the second winding.

Minelab prospecting detectors are very good at ignoring mineralisation even with the more powerful timings such as Normal or Sensitive extra in combination with Monoloop coils, however they too will react to ground minerals and when this happens gold can be masked by the mineralisation noise just like a VLF detector. To help compensate for this Minelab developed the "Smooth" class of timings of which your GPX-4500 has two, Sensitive Smooth and Enhance. These timings allow an operator to work in extremely mineralised ground without the effects of ground noise or minimal effects especially compared to the other timings. On some targets there is near Zero depth reduction when using the Smooth type timings and on others up to 20% but across the board much better than going to a DD coil and getting a reduction like 30%! Of the two Smooth class timings Enhance is better for outright depth on the majority of targets whilst still ignoring mineralisation.

However if you want to use discrimination with a GPX you need to use a DD coil which is the only way to be able to identify ferrous from non ferrous with a GPX, this also means you need to use the DD mode on the RX switch so the detector knows to transmit off one winding and receive off the other and also use the two parts to make measurements on a targets properties. (simplified explanation). To deal with interference you can either dumb down the Gain, Motion and Audio filters when using a Monoloop coil or revert to a DD and choose the Cancel mode under the RX position, by using this method you convert the DD coil to a Pseudo monoloop thereby receiving on the second winding "out of phase" (the detector ignores signals generated by both windings that are equal (mains generated EMI)) which allows the detector to ignore the pulsing of interference generated by power lines etc, because you have elected to use a pseudo monoloop mode discrim no longer works reliably, however you can also use the Enhance timings (use Fixed Ground Balance with this timing) as there will be more mineralisation noise from the coil due to the process which the Enhance timings can help deal with. I would not recommend using the Smooth type timings in DD mode with a DD coil however as a 30% reduction combined with a further reduction in signal strength from the timing will negate a lot of the advantages of the detector.

The best bang for buck coil that will compliment what you already have is a Minelab Commander 11" monoloop, that coil is slowly generating a cult following here in Australia and elsewhere as people start to realise what a top little performer it really is, and usually they are pretty cheap to buy. There are a number of aftermarket battery options depending on which country you reside but I prefer to use the Minelab offering,

Hope this helps, a lot of this information is covered in our other DVDs on the Minelab series, "Unleashing the GP series", "The Latest Update", "The GPX Factor" and or course the one you already have "The SETA Project" with another video in the works as we speak (if it ever stops raining).

Jonathan Porter

 

[Daniel Tn]

Your post really helps a lot. Thanks for taking your time to respond to it in such depth.

I came from using the Whites TDI PI machine for the last couple of years. That really opened sites up for me that had previously only been hunted with VLF machines. In some cases it was as if the sites had never been touched before with the amount of things that came out of them with the pulse machine. Since I have gotten the 4500, we have had 2 major snow storms hit....which I am just 28 years old and this is the most snow I can remember in 20 years. At any rate, it makes it rough detecting with 8 inches of snow on the ground. I have only had the 4500 out a few times in some local sites and have been amazed at the depth and thus far, what has came out that even the TDI has missed.

With that said, I am almost on the verge of getting a GPX 4800 now. I wish I could afford the 5000, but I think the 4800 would fit the bill for me. After seeing the major difference between the 4000's smooth vs the 4500s enhanced modes....I am REALLY curious as to what the new and improved timings bring to the 4800/5000. If nothing else, just the advantage of them running smoother and quieter would be worth upgrading, in my opinion anyway.

Thank you so much for doing the videos. I have also done a few instructional type videos for a couple of machines, the TDI being one of those. So I fully understand the amount of work that is involved in filming, editing, and etc.