I have now had 2 trips out to try and get to know the new GPZ 19 coil and I can tell you it has been a real eye opener.
My first trip out was to some heavily worked / raked ground, detecting with everything in factory preset. I was a little surprised that I did not find anything- I was not really expecting to though as our local goldfield here does not have the deepest of ground or the largest nuggets. I was amazed at the sensitivity of the coil on small targets though, finding a number of shotgun pellets, and one of the tiniest bits of copper wire ive ever found. With everything in factory settings I found the coil to run quite smooth but what really impressed me is how the coil handled ground noise. I would hear a noise, then on the second sweep it had diminished and on the 3rd sweep over it was gone. (this comes into play later……..)
The lack of finds puzzled me to no end and with all the negativity popping up on the forums I had to really put the old grey matter into overdrive and think about everything I know about the GPZ and ZVT tech to see if I could work out what I needed to do to get the performance claimed out of this coil.
So I have spent 2 weeks or so coming up with some theories about settings and techniques and on Friday I headed out to put them to the test.
Firstly I put some of my theorised settings into the machine, ground balanced and detected for a few mins to allow the ground balance to ‘warm up’. Placing the detector on the ground, I then began passing nuggets of different sizes and types over the coil to get an idea of depth.
I was quite impressed with the clarity of signal from all of the nuggets 30grm and up. I did notice that some smaller pieces would signal at a much greater depth than some of the bigger ones (ie 31grm vs 53grm)- which I think is where some of the negativity surrounding this coil has arisen from. It has become clear since starting to use the gpz that each nugget, regardless of weight, can be detected at its own depth, depending on its physical size, shape, surface area and orientation. I have a half gram flat ‘cornflake’ nugget that gives more depth than a solid, irregular shaped 3 grammer. I also have a solid 2 grammer that has a very bubbly surface, that is invisible to the pulse induction machines (GP/GPX/SDC) yet air tests at 34cm when presented broad side to a GPZ, and when presented with its end will only signal at 5-10cm.
So I have come to the conclusion that many of us are getting hung up with depth testing on these known targets. we don’t know what is still out there or what depth we will find them- so the need to focus on understanding and setting the machine has now become my primary objective.
So what settings are you running?
Here are the settings I came to that I felt gave the smoothest operation, the clearest target response and best depth. Be warned- you will need to use a very different detecting technique to use these settings - but that’s what the GPZ is about! It’s a new tech, and we need to re learn some things to utilise its full power.
First thing we need to do is re-set the machine to factory presets. I find the quickest way to do this is to select the quick start icon, then it will prompt you to reset the detector and audio settings. When you select reset, it will begin the auto noise cancel- press the return button now and it will bring you back to the main detect screen.
I do the reset this way for 2 reasons. To dump the ground balance data from previous detecting sessions and to not disconnect my wireless module!
Now put in the following settings-
Gold mode - High yield
Ground type - Normal
Sensitivity - 4 ( yes that’s right 4!)
Leave everything else on factory preset except volume, which I took up to 10-12, and detector tone (this is your own preference- my sweet tone is 33)
Now perform an auto noise cancel.
Next, we need to ground balance using the ferrite ring. This is very important as we need to make sure our initial ferrite balance is correct. Depress the quick track trigger and sweep the coil over the ferrite ring and ground, taking in as much ground and the ring with each sweep as you can. I find if I move around the ferrite ring as I sweep, it allows me to take in lots of ground thus helping the machine to get a better picture of the ground mineralisation. It is important to keep the coil about an inch off the ground while balancing, keeping the coil as level as possible. After about 10 seconds of sweeping over the ferrite and ground, release the trigger, and bob the coil up and down. If the threshold does not smooth out within a few seconds, or if you still hear the ferrite ring, depress the trigger and try balancing again. When correct balance is achieved, you should find the threshold smooths out quickly when you bob the coil after releasing the quick track button. If you still can’t get it right, then back the sensitivity down to 3 and try again! I can’t stress enough the importance of getting the initial ground balance right! If it is not right, the gpz will react too much to the ground resulting in unwanted noise- and these settings are centred around removing as much noise as possible, allowing all the audio from targets to come through.
Next, change the gold mode to general and repeat the ground balance procedure above.
Now we are ready to do some depth testing (if you must…….) or get detecting.
This is where we need to start re-learning how to detect……
I think they key to success with this coil is not to just wander aimlessly, but rather be super thorough. To help with this I would suggest putting your pick down, marking out an area of say 20m by 20m and cover every inch of it, marking suspected targets with a boot scrape, then come back with the pick and investigate.
When detecting in normal, it is important to keep the coil about an inch above the ground to stop from saturating the soil with signal, causing noise that could hide a target. Use a slow and controlled sweep speed, say 3-4 seconds per meter to allow the ground balance to work properly- sorting the ground noise from metallic signal.
When a ground noise is encountered- and you will encounter many- sweep the coil not only over the noise but well beyond. This again will enable the ground balance to build up information and start to cancel out the noise. I found many ground noises would disappear with a few sweeps, or change in response. If in doubt, bob the coil over the noise, and it will usually disappear and throw off the ground balance around it. If this happens, simply bob the coil away from your ground signal to bring it back into line. Now if it is indeed a target, bobbing the coil over it will not cause the signal to dissipate, nor will it throw the ground balance off away from the target. If in any doubt- dig it!
Now, after all that, what did I find?????
Well after about 5 minutes I heard a distinct but quiet double signal. I thought it may have just have been a pellet or the such at first- but how could I have missed that with the GPZ 14 coil? I scraped away the leaf litter and loose soil, and the double signal remained. Calling my mate over, we removed the top 2 inches and the signal brightened up and became a sweet single response. Taking more soil out it got louder. We were careful to take it slow to ensure we got the target from the bottom of the hole. Pinpointing was surprisingly easy with the big coil and we were confident it was dead centre in the bottom of the hold. With one more scrape the signal was out and was sitting directly on top of the pile next to the hole. To my amazement from a depth of 6” in the ground + 1” of leaf matter and 1” of height of coil above the ground- it was a whole 0.57 grams!
We measured with a ruler just to be sure we weren’t guessing! After a quick drink my mate had to head away leaving me to it.
Then about 1.5 feet in front of that one I got another very clear signal. Very distinct from the ground noise. Much more concise and symmetrical, and wouldn’t balance out.
I could tell it was deep so knocked 3 inches out to start and the signal perked up a little. So 3 more inches out and it got better. Now I was getting excited……
Well after some more digging, the target was loud now and I was able to pin point it with the coil. I benched out one side of the hole to allow better pin pointing with the coil, then switched on the pro-find pin pointer and could just pick it up. So again being slow and careful took little by little out to make sure I wasn’t going past the nugget. I was right on top of it in the centre of the hole with the pin pointer, and out popped a nugget of 1.75 grams!
I measured the depth at 34cm to the soil surface, but again about another 1” of leaves and the coil was about another 1”off the ground. Before digging I noted I could hear the signal about 4” above the ground clearly. I was stoked!
I won’t tell you about the 35grammer I pulled in another spot about 300m away…….
Except that it was in a hole that took quite some time to dig, was about 69cm deep and turned out to be a slug of lead painted gold!!!!!!!!!