It's pretty difficult to compare the PI Metal Detector and VLF metal detector technologies, relating to gold detecting as they are very different types of machines.
...But for WA conditions the metal detectors that will find you the most gold nuggets are the Pulse Induction metal detectors like the Minelab 4500.
Attached is a link to the compare metal detectors page, perhaps that will assist you with the decision YOU need to make to purchase the detector YOU need for your metal detecting profile.
Here is some information from the book written by Dave Johnson Chief Designer Fisher Research Labs which is available at this link; How VLF Metal Detector works.
How VLF Metal Detectors Work
The searchcoil assembly (also called search head or "loop") contains two electrical induction coils which are like antennas.
One coil is a transmitting antenna which is surrounded by a rapidly alternating magnetic field. If metal is present, the alternating magnetic field will induce current to flow in the metal.
The other coil in the searchcoil assembly is a receiving antenna which detects changes in the magnetic field caused by the electric current circulating in the piece of metal. Electronic circuits amplify this weak signal, analyze it to determine the changes which occur as the searchcoil sweeps over the target and then convey the information to the user in the form of a visual display or audio tones.
Most modern metal detectors perform some of these tasks in software running on an internal microcomputer.
The iron minerals which are present in most soils distort the magnetic field, obscuring the weak signals of small or deep metal objects. This can cause the object to go undetected, or to be misidentified when it is detected. Much of the technology that goes into modern metal detectors is devoted to the task of eliminating the unwanted signals from iron minerals in the soil, while not losing the signals from metal objects.
This book is a good read on VLF metal detectors with plenty of information about how to use the VLF metal detector and metal detecting in general.
The VLF coil generates a continuous low power transmit signal via the transmit coil antenna then analyses the amplitude and change of the signal which is generated by a target through the separate receive coil antenna.
Theoretically the signal of an object can be analysed to determine the type of metal that has created the signal.
Unfortunately the VLF detector will respond to magnetite and other hotrocks and overload in some of the conditions encountered in the WA Goldfields whereas in the same conditions the PI detector will not create a response.
Price - much cheaper than PI Machines
Weight - Much lighter than PI machines.
Less Power Required
Small Nugget Detection, Usually better in VLF machines, particularly with small coils. This is totally lost in magnetite or hot rock areas because of noise and overload of the VLF circuits.
Can get a multipurpose machine for gold, coin and relic hunting
Metal Discrimination mode, to deal with iron trash.
Not as sensitive to electical interference.
Discrimination, This is also a Disadvantage because it can entail loss of sensitivity to gold.
Hot Rocks and Mineralisation, Hot rocks and Mineralisation will affect the VLF machine much more than the PI detectors.
Does not have the depth of a PI
That is also a difficult question which will depend on what you want in a metal detector and what you will use it for.
If you want to specialise in finding gold nuggets in Western Australia as more that just a once a year hobby, and PRICE is not your key issue then a top range Pulse induction metal detector like the Minelab 4500, 4800 or 5000 is a very good choice.
Remember too that if you look after this machine it will have a good resale value after use - check out sales on ebay or other sites!
Dont waste your time on lesser or old technology - its just false economy.
Alternatively a Second hand Minelab 4000 or 4500 will save you $000's and still do as good a job for you.
For example now the Minelab 5000 metal detector has been released, Minelab 4500 machines are readily available second hand for about $Aud4500. whereas a new 5000 machine will set you back $Aud6700 - the technology of the Minelab 4500 is excellent for finding gold in Western Australia.
If you just want to use a metal detector occasionally when you are travelling to look for a few coins or relics with the odd trip gold prospecting then a good VLF Detector or a lower price range PI Detector might be quite OK for you.
If you want a waterproof detector for beach hunting or underwater detecting then you can also get models that are designed for land and underwater use.
Here is a link to a page where you can compare metal detectors.
That page also has a link to software that enables you to make an informed decision on any question you would like to ask, including the type of metal detector that is best for you.
If you review this page and the Pulse induction metal detector page it will help you make a more informed decision based on your needs and the criteria you want to use when selecting a metal detector and coil combination.
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