This article relates to VLF (Very Low Frequency) metal detectors, which account for most hobby detectors as well as some gold detectors on the market today.
If you look at the specifications of the metal detector, you will find a frequency that the machine runs at.
Garrett ACE 200i – 6.5 kHz
Nokta Simplex+ – 12 kHz
Minelab Equinox 800 – Multi, 5, 10, 15, 20, 40 kHz
Nokta Gold Kruzer – 61 kHz
So what do these numbers actually mean and should you worry about them?
Well this depends, if you a just want a machine to have some fun with in the park to see what you can find, then no, it’s not all that important, however if you are looking for a specific item like shallow gold, then yes, you would want a machine that runs at the correct frequency to help best find what you looking for.
Let’s start with depth – The lower the frequency, the better depth you will get. As you start increasing the frequency, you will start to sacrifice on depth.
Well that’s easy then, we all want as much depth as possible, so let’s all use machines that have low frequencies then…. well no, it’s not quite as simple as that which brings me to my next point…
The size of the target – To find really large targets, you would want to use a low frequency. A massive drain cover for example, a low frequency here will be perfect as you looking for a large target and will get you the best depth. Now if you out to look for tiny sub gram gold nuggets, then you would not want to use a low frequency but rather a much higher frequency. By using a high frequency, when you sweep over the tiniest target it can provide a good solid signal whereas a really low frequency could miss this tiny target altogether. The higher the frequency is, the smaller the target can be while still receiving a good signal from the detector as sensitivity is increased.
The conductivity of the target – Different metals have different conductive properties. Silver for example is a high conductive metal whereas gold has low conductive properties. Low frequencies are better suited to high conductive metals (such as silver) whereas high frequencies are better suited to low conductive metals (such as gold).
So that is why you will notice that most VLF Gold Machines are considered specialist machines which run at a much higher frequency than most hobby detectors for these exact reasons – to be able to provide a solid signal to the tiniest of sub gram gold nuggets out in the goldfields as well as to provide a good hit on the low conductive properties of gold. The Minelab Gold Monster runs at 45 kHz, Nokta Gold Kruzer 61 kHz and XP ORX with 9.5″ elliptical coil has selectable frequencies from 14 kHz all the way to 81 kHz, making it an excellent choice for gold prospecting as you can change the frequency depending on ground conditions (The higher the frequency, the more susceptible the machine will be to giving false targets in highly mineralised ground due to the increased sensitivity).
Some metal detectors come with one frequency only which can be limiting, some come with a range of frequencies that you can manually select from and some of the newer machines come with a multi frequency option which can run at multiple frequencies simultaneously.
I would suggest that it is usually better to manually select one frequency if you searching for something in particular, otherwise run on multi frequency if your machine has that option to give you the best average of all the frequencies to give a good signal on a wide range of metals.
Here is a video that Minelab posted on their multi IQ technology which uses multiple frequencies simultaneously:
This is not to say that a low frequency machine cannot find gold or a high frequency machine cannot find silver – this is not the case at all but it just improves the detectors ability to find exactly what you searching for – using the best tool for the job!