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.
This range from 3Hz to 300GHz has been split into regions.
The good thing is that once this range 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? Instead, 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.
On some documents that describe electromagnetic
spectrum you might see terms like LW, MW and SW. In a lot of occasions
you might see them mixed in the same context as frequency range
we mentioned above. For example here is a quote from one webpage:
''...extends thru LW, MW, HF and VHF.''
This is wrong!
We talk apples
and oranges here. LW is not LF, and MW is not MF, therefore you
can't put them together in same context with HF and VHF.
LW, MW and SW are frequency designations of AM broadcast
radio stations, and thats about it. They have nothing to do with
ITU's band designations we mentioned in the table above. Some countries
don't even have LW, so you should not mix LW, MW or SW with
HF, VHF etc. unless you are talking about AM broadcast stations. To be exact MW and HF should never
be mixed together in the the same context. Here is the frequency table
for AM broadcast bands:
Designation
|
Name
|
Frequency
|
LW
|
long wave
|
153
- 279 kHz
|
MW
|
medium
wave
|
531 - 1620
kHz
|
SW
|
short wave
|
2310
- 25820 kHz
|
|