In the Goldfields

Well it’s nearly a year now since the release of Minelab’s most potent gold prospecting machine ever the GP3500, and of course as with anything new it takes a while to find out what makes ‘em tick. One of the most astounding things I noticed this year had more to do with actually not making any adjustments to any of the controls at all rather than switching from one mode to another, now in my case I could do this because I was working solely with the big Nugget Finder Mono’s and the ground although noisy in places did not require the use of a lot of the other features of the GP platform such as Sensitive mode, Cancel mode, Salt Mode etc…. (this was mainly due to the new MEDIUM GB speed option (YES I tend to detect in TRACKING mode all the time now).

But what did come as a major surprise was the new Quick Trak control on the handle of the machine, as most readers would already know plenty of GP users had already implemented their own basic push button GB control on the handle of the previous 2 GP models, but in truth this really was a stop gap only measure and in some cases a major cause for concern because of interference generated by a lack of correct shielding on the wiring harness. With this in mind I would also say there would be a pretty tight grip on the sale of replacement Quick Trak GB control buttons from Minelab for the fear that GP3000 users tried to plug into a GP3000’s smart point which could cause the unit to wipe its internal program because of a perceived breach of its very tight internal security code.

As an aside one of my biggest concerns when I first tested the GP3500 was a perceived delay from the moment of triggering the Fast Trak and the actual internal electronics performing the task, this was not such an issue when in the tracking mode because the electronics go into a FAST GB anyway but what about when you’re in FIXED GB? As you can imagine pushing a button with your thumb is a bit of an unnatural position especially when you are holding close on three kilo’s of metal detector with nothing but a flexible piece of rubber between your self and complete exhaustion. Most of us tend to roll our wrist which concerned me because a mono coil requires an almost perfect aspect to the ground to gain what I call acceptable/perfect GB. This is not such a problem with the smaller monos but with something as large as a 20” Nugget Finder (although they are very light) can be of major concern. The perceived delay was a left over from the original GP extremes and caused me a fair bit of angst, although Minelab’s techs did allay my fears. The delay I am talking about is when you are in the FIXED GB mode and trigger the Quick Trak feature on the handle, if you pay careful attention to the audio you should notice a slight ping/chirp (very slight) as the button is released as if the GB has slightly gone out of whack.

This little chirp would give the impression that the GB was not quite right and caused me to waste many hours a day going back through the procedure of re-ground balancing, just to be sure (sounds a little obsessive compulsive doesn’t it?). This effect could sometimes be noticed on the extremes and 3000’s when you went from Tracking to Fixed on the GB switch. As you can imagine if the switch was even further away the delay could be even more pronounced, but thankfully this has proved to not be the case with the 3500. However if you are trying to re-Ground balance in the FIXED GB mode then pay attention to how much roll you have on your wrist as the button is released, personally I would recommend users to use the onboard GB switch on the front end cap (coil side of the control box) rather than the Quick Trak option because you have more control and less tendency to roll the wrist (this is only for FIXED GB use).

However you need to keep in mind a mono coil can go out of balance in the blink of an eye; that crucial moment as you release the button is vital for accurate GB especially if you are working in FIXED GB for maximum depth. Basically if the wrist is rolled that last split second it forces one edge of the coil to come nearer to the ground which can cause the GB to go out of whack fractionally. The little chirp mentioned earlier is an inbuilt quirk which could mask an "out of whack" GB response as the button transitions from on to off.

During a private viewing of our latest video “The Outback Prospector – The latest Update” I was asked why I have so much air between the coil and the ground during some of the test bed scenes; my answer was simple, it is because a mono coil does not like to be scrubbed right on the ground, especially if the ground is extreme! I tend to run a mono coil at least 50mm above the deck (see our first video for more info) to allow a buffer between the grounds extreme surface minerals and the coil, so as not to saturate the coils magnetic field. If you dip an edge of the coil into this buffer after performing a GB at a set height you can throw the whole GB out of whack (as described above), because the electronics see the ground completely differently once the coils original plane has been altered. BTW the 50mm distance is not a “set in stone” measurement but a guide only, as long as you GB to the same height and detect at that height things will be fine, be prepared to experiment as some ground will allow much closer coil heights depending on the internal GB position. Also as an another aside generally the smaller the coil the closer you can get a mono to the ground which explains why the larger coils tend to miss a few of the smaller shallow pieces.

Now getting back to the purpose of this post, the Quick Trak control on the GP3500 handle is a very powerful feature especially with the mono coils because it allows the user to GB quickly on the FLY without even pausing for breath. This feature is very powerful with Mono coils but I am sure it will benefit DD’s as well. Just to explain the DD coil situation, DD coils tend to perform a mild sort of GB (NULL) in their own right and as such don’t require the “extreme’s of GB” a mono coil needs to achieve a null (position where the machine ignores the ground signal). What I have found out is this, when prospecting large amounts of ground rather then stopping to re-ground balance to a perfect position for that exact spot I hit the Quick Trak on the FLY (OK I admit it I’m in love with that little bird chime from the machine) without even stopping my swing or stride, this then causes a forced GB to be performed which then provides a MEAN of the immediate area rather than a specific GB of a fixed position (remember you have 3 to 5 seconds of forced GB). I will perform these on the FLY GB actions on a regular basis but usually when the machine is starting to warm up (a bit more ground noise) or becomes vociferous, but generally I’ll conduct one of these on the FLY actions every few minutes or so (the old obsessive compulsive thing again!). Now for those of you concerned about missing a target at the crucial moment the Machine conducts it’s FAST FORCED GB, don’t worry because I’ve pinged nuggets both deep and shallow when this is happening with out any problems.