Better Understanding Zero Voltage Transmission (ZVT)

Following on from my last blog about the GPZ 19 coil, here are some further tips to help you get the best from your GPZ 7000, irrespective of which coil you are using.  The GPZ 7000 is not difficult once you come to terms with the way the technology performs over the ground. It is a blend of behaviours which are dictated by ZVT technology, the Super-D coil design and the detector’s ability to tap into the full gamut of target information, thanks to being able to run a very low noise floor without any major trade-offs to audio stability.

The key points for better ZVT understanding are:

• Conservative Sensitivity and target Volume settings
• Obtaining and maintaining a good ferrite balance
• Keeping on top of the Auto Tracking ground balance
• Effective range of coil motion relative to target depth
• Knowing your detector settings (recap from previous blog)

Let’s consider some of the specifics…

Conservative Sensitivity and target Volume settings

It is important to understand it is the ZVT technology that is the driving force behind the GPZ 7000, not some insane amount of Sensitivity level or Volume control settings. Learn to be conservative when making adjustments. Deep signals do not improve greatly when the Volume or Sensitivity is increased, threshold noise and ground instability do.

Imagine two lines one above the other, with your Threshold Level being the baseline volume and the maximum signal response as being the detector’s loudest possible response as the top line. Obviously you need to be able to clearly hear the threshold so that determines your baseline. However, by increasing Sensitivity or Target Volume or both, you will compress the important information that resides between your baseline and maximum volume. This is because the maximum target volume has a top out point so the detector’s target signal audio response has to live within those two physical constraints.

Obtaining and maintaining a good ferrite balance

At no time should there be any Ferrite signal. If the GPZ 7000 makes a signal on the Ferrite it will also make a signal on ground mineralisation that presents the response to the detector’s electronics. This can potentially mask good deep gold targets.

Keeping on top of the Auto Tracking ground balance

I generally operate in Auto GB mode, but I also configure the User button so I can quickly place the GB in Manual mode when I want to actually start removing soil to get the coil closer to a potential target. I do not recommend continually passing the coil over a target in Auto mode. Four or five times should be sufficient, but then I ‘pump’ the coil nearby to get the GB back to the local ground condition before passing the coil over the target zone again.

Effective range of coil motion relative to target depth

The transmit field of the GPZ 7000 is very powerful and travels a long way from the coil into the ground to effectively ‘liven up’ any targets within range. However, the resultant field generated by the target itself can be very weak and so requires careful sweeping of the coil to get the target signal in the sweet spot of the coil’s receive areas. This requires a good combination of motion range and sweep speed to achieve and is probably the most constantly changing aspect of my detecting sessions when using the GPZ 7000. The coil has to be in motion to generate a signal response. The more refined you can make your sweep speed and range of movement of the coil, the greater your chances of achieving a good clear target response.

Knowing your detector settings

The GPZ 7000 is a very powerful metal detector, but target signals do not always just ‘jump out’, especially the deeper ones, they require input and interpretation from the detector operator. The smoother and more controlled you are, the better the results. Learn to trust what ZVT is ‘telling’ you. It is the fundamental reason why ‘good gold’ is coming from the goldfields all over again.

The typical settings I have used for best results are:

• Sensitivity: 9
• Audio Smoothing: Off
• Volume: 8 for headphones/B&Z Booster, 12 for WM 12
• Threshold: 27
• Threshold Pitch: 60
• Volume Limit: 8 to 12
• Ground Balance Mode: Auto
• User Button: Ground Balance Mode

Keeping the word “control” at the forefront of your mind at all times, while using the GPZ 7000, will pay dividends. Repeatability and consistency should be your mantra, combined with a decent range of coil movement to afford a subtle deep target every opportunity to be recognised for what it is. Best of luck out there using the most powerful detector I've ever encountered!

Jonathan Porter

Aurum Australis 

To read more about the GPZ 19 Super-D coil, click here.