What does frequency mean when metal detecting?
A common definition of frequency is as follows: The number of waves per unit of time measured in Khz or kilohertz. In a metal detector this is the number of electronic waves sent into the ground to detect metal.
Example: 10 Khz means your detector will send and receive 10 000 times per second.
Why is Frequency important?
- Both Pulse induction and beat frequency oscillator type metal detectors use frequency of electronic fields or pulses sent into the ground.
- Different frequencies have different advantages and disadvantages when metal detecting.
- Metal detector frequencies range between 3 – 100 Khz as a general rule.
- Have longer wavelength.
- Gets greater depth as long waves penetrate the ground more easily.
- Better for detecting high conductivity targets like silver.
- Not good for finding smaller targets.
- Not good for low conductivity targets like gold or Iron.
- Have shorter wavelengths.
- Great for detecting small objects like tiny gold nuggets.
- Better for low conductivity targets like gold and Iron.
- Less depth is achieved than low frequency.
- Higher accuracy, closer to the surface.
- More sensitive to ground mineralisation interference.
Most hobby detectors use a middle ground to try and get the best of both frequencies in the Goldilocks zone around 6 – 8 Khz for the best depth and sensitivity trade off. Some detectors even let you manually set the frequency on your detector. Others even use multiple frequencies at one time.
2 types of Frequencies:
Single Frequency operation: Also called continuous wave has only one frequency selection. This is usually found in the Beat Frequency Oscilators like the Garrett Ace 250. This type is most often found in Entry level machines.
Multiple or Dual Frequency operation: Some more advanced metal detectors make use of more than one frequency at the same time. Examples of this can be found in the Minelab Excalibur II, Etrac and CTX 3030. This is often called full band spectrum frequency technology allowing the user to get the best depth and accuracy at the same time. This is more often found on Pulse induction machines.
Metal Detector Frequency Comparison Chart:
|Garrett||Ace 150||Single||6.5 Khz||Beat frequency.|
|Garrett||Ace 250||Single||6.5 Khz||Beat frequency.|
|Garrett||Ace 350||Single||8.25 Khz||Beat frequency.|
|Garrett||Sea Hunter||Multiple (manually adjustable)||7.5 Khz||Pulse induction.|
|Garrett||AT Pro||Single||15 Khz||Beat frequency.|
|Garrett||Infinium||Multiple (manually adjustable)||7.3 Khz||Pulse induction.|
|Garrett||GTI 2500||Multiple (manually adjustable)||7.2 khz||Pulse induction and Beat frequency.|
|Garrett||AT Gold||Single||18 Khz||Beat frequency.|
|Minelab||GPX||Multiple (manually adjustable)||Multiple specially calibrated to conditions selected.||Pulse induction.|
|Minelab||Eureka Gold||Triple||6.4, 20, 60 Khz||Pulse induction.|
|Minelab||Xterra 305||Single||7 Khz or 18.5 Khz with a different coil.||Pulse induction.|
|Minelab||Xterra 505||Single||7 Khz or 18.5 Khz with a different coil.||Pulse induction.|
|Minelab||Xterra 705||Single||7 Khz or 18.5 Khz with a different coil.||Pulse induction.|
|Minelab||Xcalibur 2||Multiple (17 concurrent)||1,5 – 25,5 Khz||BBS Broad band spectrum Pulse induction.|
|Minelab||Etrac||Multiple concurrent||1,5 – 100 Khz||FBS Full band spectrum Pulse induction.|
|Minelab||CTX 3030||Multiple concurrent||1,5 – 100 Khz||FBS Full band spectrum Pulse induction.|
Frequency and Conductivity.
Metal objects in the ground all conduct electricity better or worse. This may be plotted on a scale from Ferrous iron on the low side to Non Ferrous silver on the high side with gold and foil somewhere in the middle. This is often the basis for the LCD screen layout as you can see on the Garrett Ace.
Hobby metal detectors can tell the type of metal by how well it conducts electricity of the frequency pulses it sends into the ground (usually the speed that the signal sent back decays over time.) This allows the modern hobby metal detector to discriminate between metals and not only indicate the type of metal it thinks it’s found but also allows you to screen out certain metals like iron if you want to stop the detector from picking them up.
Whether it is a simple single frequency machine like the Ace 350 or a complex machine like the Etrac using 1 – 100 Khz at the same time frequency is an important consideration when making your purchase.
We hope this helps your choice and understanding of a hobby metal detector and frequency!
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