GPX series detectors Are these as complicated as people think? To decide the answer to this question we need to investigate the settings and adjustments. If we look at the front panel starting where the coil lead plugs in, we find a Fixed/Tracking switch. In conjunction with the green button in the handle (and this applies to the GP 3500 also) we have the choice of detecting in automatic ground balance mode, or fixed. As the name applies, fixed means that we have “set” the ground balance to a figure, and when the ground mineralisation levels change we need to manually readjust this setting. Tracking means that the detector will automatically adjust (track) as we detect, and we have a choice of how fast this happens with the slow, medium or fast option in the menu. Medium is the recommended option, so we can set this and forget it for the most part. (most of the Minelab PI’s have this except for the SD2000 and SD2100) The next choice is the Coil RX, and again, this was on the GP Extreme and up (names were different). This determines how the electronics treat the coil being used in relation to how the transmit and receive areas are. There is a lot of information in the owner’s manual about how this works. We then have the Soil switch. This switch determines what soil timing we are using from the selection available. All Minelabs from the SD2200 have this switch although the choices are different in the later GPX models. The last toggle switch is the Mode switch. This switch has 3 positions being, Deep, General and Custom. Each of these names is just that, a name. Deep, for example does not search deeply if you have modified the menu settings. These could have been called A, B and C or whatever you can think of. These 3 modes are capable of being customised to suit different applications. I tell customers that the easiest way of thinking about these 3 modes is to consider you have 3 different detectors at the flick of a switch. I set up Deep to look for deeper nuggets with a larger mono coil, General as a day to day platform for small or large coils, and Custom (which is called Patch in the menu unless it has been changed) as an EMI blocker. Thus we can switch between modes without having to fiddle in the menu and we get more detecting done. The threshold rotary switch is set on the front panel and basically forgotten about, much like the predecessors except the SD2000 and SD2100. (The GP3500 was different as it incorporated the on/off switch also) Lastly we have a push button for tuning out interference (Auto tune - which has been there since the SD2200) OK, so the switches on the front for the most part have been there since the SD2200 days. Those detectors and subsequent ones that followed also had switches on the rear panel for signal, tone and volume which are now in the menu, and another timing switch which is also a menu item now. The battery voltage is just to tell us how charged it is and we cannot change it in any way. The discriminator control (for those brave enough to trust it) is in the menu. The volume control is in the menu. The tone control is in the menu. The Signal control is in the menu. The manual tune (3500 and up) is in the menu. The audio control is in the menu. The tracking control switch is in the menu also. So the major differences are; 1. A second volume control that limits how loud a target can be so we don’t damage our hearing. 2. A backlight so we can see the screen more easily (4500 and 5000). 3. A selection of ground balance types that we usually run at General. 4. A timing selection which was previously a switch on one of the panels. 5. A motion control. 6. A gain control. 7. A Stabiliser control. Items 4 to 7 are the ones that we are concerned with, and are the items that actually get changed as numbers 1 to 3 are set and forget mostly. Looking at this means that the “supposedly” complicated GPX models have not that many differences to most of the earlier machines, specifically the motion, gain and stabiliser controls. We will deal with these in another document.
This document explains the basic differences with a GPX series detector as opposed to the earlier offerings, and hopes to remove some of the myths. GPX5000, GPX4800, GPX4500, GPX4000.
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GPX Series Detectors