How do VLF detectors work?
Very Low-Frequency detectors are considered to be the most versatile type out there, based on the range of metallic objects it can actually find for you.
VLFs function with 2 distinct coils. These include:
- Transmitter coil: This is the outer coil loop, within which is a coil of wire. Electricity is passed along this wire, first in one direction and then in the other direction. The electricity passed can even go up to thousands of times per second.
- Receiver coil: This is the inner coil loop, which contains another coil of wire. It is what acts as an antenna to pick up and then amplify the frequencies that are coming from target objects in the ground.
This is getting a bit technical, but please bear with me for a second! (btw, if you don’t care about this technical part, just skip to the next paragraphs)
So, to make it simpler for you, just keep in mind that the electric current that moves through the transmitter coil creates an electromagnetic field …
… The polarity of this magnetic field is perpendicular or opposite to that of the coil of wire. So every time the current changes direction, the polarity of the magnetic field also changes …
… This means that if the coil of wire is parallel to the ground, the magnetic field keeps constantly pushing down into the ground, and then it pulls back from it!
As this magnetic field keeps pulsing back and forth into the ground, it also interacts with any conductive objects that are present in the ground. This causes them to generate weak magnetic fields of their own.
The polarity of the target’s magnetic field is going to be directly opposite to that created by the transmitter coil’s magnetic field:
For example, if the transmitter coil’s field is pulsing downwards, then the object’s field is going to be pulsing upwards.
When the receiver coil passes over this object that is giving off a magnetic field, a small current travels along with the coil that oscillates at the same frequency as that of the object’s magnetic field.
The coil then amplifies this frequency and sends it to the control box of the VLF machine, where the sensors analyze the signal they receive.
The machine can roughly determine the depth at which the object in question is buried based on the strength of the magnetic field it is generating.
The closer to the surface an object is located, the stronger will be the electric current it creates. The farther down the object is, the weaker will be this field.
After a certain depth, though, the object’s magnetic field becomes so weak by the time it reaches the surface that it becomes undetectable by the detector’s receiver coil.
VLF vs PI Metal Detectors – What’s the difference?
Pulse induction (PI) is a more sophisticated type of detecting technology … Indeed, it involves a high voltage pulse that is sent into the ground.
The PI technology does not get affected by ground minerals, unlike VLF detectors … That’s they are the Best choice when it comes to gold prospecting!
Below a table that gather the main differences between the 2:
| Feature | VLF | PI |
| Frequency | Mostly Low | Operate on Higher frequencies |
| Constant Swinging | Required | Not Required |
| Mineralized Soil | Could be affected | Not Affected |
| Targets Size | Big and Average | All including small ones |
| Price | Low to Medium | Medium to High |
| Weight | Light | A bit Heavier |
| Battery Power | Require less Power | Require More Power |
| Purpose | Multi-purpose | Mostly Single |
| Discrimination | Need to be Set | No Discm per default |
Do VLF detectors operate deep enough?
The depth till which a Very Low Frequency device can detect depends on several factors, including the machine itself, size, and ground conditions, etc.
A typical good model can easily detect up to 6 to 10 inches below the ground for objects like coins and those with similar size. This could decrease quite a bit if you are dealing with smaller objects …
Anyway, below some of the other factors that can affect the depth:
- The amount of discrimination you have set on the detector: If you have not set proper discrimination, or your machine is just not able to, then you won’t be able to locate deeper targets through the trash metals in the ground.
- Metallic composition of the object: Certain metals have higher electrical conductivity, for example, brass, copper, and silver. Other metals do not have sufficient conductivity, for example, stainless steel. Therefore, it is harder to detect the latter type of metals at higher depth.
- Proximity of the object to other larger metallic targets in the same area also affects the depth of your detector.
- The machine’s sensitivity setting: Generally higher sensitivity means less in terms of depth and vice versa.
- Coil’s size: If you use a bigger coil, you will be able to go deeper, just make sure your machine supports that.
What coil design work for VLF machines in general?
There is really no better choice, the only factor is whether you want to go deeper with less sensitivity (Bigger Coil) or more sensitivity with a bit less depth (smaller Coil) …
Another thing you may want to consider the weight, that is, a larger coil generally means a heavier machine … However, since VLFs are generally light, then it wouldn’t really matter if you use a larger searchcoil.
Finally, make sure to check the manufacturer recommendations for the exact model you are using. They are the one who designed it, so they just know what would work best for it.
Just, please don’t bother yourself with these details until you’ve gained some experience!
Conclusion
I really wanted to go into some nerdy details, so not only you will know the right detector you should use, but also to understand how this kind of machines actually work … (Hope this was not boring lol)
… If you are a beginner, understanding all these features won’t come overnight, yet after you’ve understood all these features you will always have an edge selecting a good vlf detection device and also using it properly!
