Definition of frequency bands (VLF, ELF... etc.)
text by: Tomislav Stimac (http://www.inet.hr/~tstimac/contacts.htm)
For too many times I've seen wrong usage of terms like VLF, ELF and similar.
As a matter of fact if you go and look over the web in articles connected with
VLF, you'll see that almost everyone uses different term for something that
is ELF, or SLF or vice versa. In some article you will read that 4kHz is ELF,
while the other article you'll read that 4kHz it is VLF. So where is this 4kHz
anyway? And what is difference between ELF, ULF and VLF?
Each frequency range has a band designator and each range of frequencies behaves differently and performs different functions. The frequency spectrum is shared by civil, government, and military users of all nations according to International Telecommunications Union (ITU) radio regulations. For communications purposes, the usable frequency spectrum now extends from about 3Hz to about 300GHz. There are also some experiments at about 100THz where research on laser communications is taking place but we won't discuss this now. So this area from 3Hz to 300GHz has been split in some regions. The good thing is that once this area has been split it remained that way and became standard. And it is up to you if you want to accept this standard or not. Frequency band standard is described in International Telecommunications Union radio regulations. And it looks as follows.
Designation |
Frequency |
Wavelength |
|
ELF |
extremely low frequency |
3Hz to 30Hz |
100'000km to 10'000 km |
SLF |
superlow frequency |
30Hz to 300Hz |
10'000km to 1'000km |
ULF |
ultralow frequency |
300Hz to 3000Hz |
1'000km to 100km |
VLF |
very low frequency |
3kHz to 30kHz |
100km to 10km |
LF |
low frequency |
30kHz to 300kHz |
10km to 1km |
MF |
medium frequency |
300kHz to 3000kHz |
1km to 100m |
HF |
high frequency |
3MHz to 30MHz |
100m to 10m |
VHF |
very high frequency |
30MHz to 300MHz |
10m to 1m |
UHF |
ultrahigh frequency |
300MHz to 3000MHz |
1m to 10cm |
SHF |
superhigh frequency |
3GHz to 30GHz |
10cm to 1cm |
EHF |
extremely high frequency |
30GHz to 300GHz |
1cm to 1mm |
However, to simplify things about VLF a good idea would be to use term audio frequency range. Imagine doing a project covering 20 Hz to 20 kHz, it would be annoying to write ELF/SLF/ULF/VLF all the time. But again it would not be correct if you just write VLF because there is much more in that range. Right? So you can simply use term 'audio frequency range'. As I said in the beginning there are already dozens of articles with wrong frequency designations and a good thing would be to correct and minimize mistakes. Here below is a simplified version of above table. It is a silver plate that I've made to help you to remember frequency range designations since lot of us have tendency to forget tables, but we don't forget images that easy.