ULF, ELF, VLF, LF, HF, VHF

1) Extremely low frequency (ELF): 0 to 300 Hz
United States Government agencies, such as NASA, describe ELF with ranges between 3 to 30 Hz, >0 to 300 Hz, and even, according to WHO, >0 to 100 kHz. At frequencies this low (>0 to 300 Hz), "the wavelengths in air are very long (6000 km at 50 Hz and 5000 km at 60 Hz),

2) Ultra low frequency (ULF): 300 hertz and 3 kilohertz
is the frequency range between 300 hertz and 3 kilohertz. Many types of waves in the ULF frequency band can be observed in the magnetosphere and on the ground. These waves represent important physical processes in the near-Earth plasma environment. The speed of the ULF waves is often associated with the Alfven velocity that depends on the ambient magnetic field and plasma mass density. This band is used for communications in mines, as it can penetrate the earth.

3) Very low frequency or VLF : 3 kHz to 30 kHz
refers to radio frequencies (RF) in the range of 3 kHz to 30 kHz. VLF waves can penetrate water to a depth of roughly 10 to 40 metres (30 to 130 feet), depending on the frequency employed and the salinity of the water. VLF is used to communicate with submarines near the surface (for example using the transmitter DHO38), while ELF is used for deeply-submerged vessels.

4) Low frequency or low freq or LF: 30 kHz–300 kHz
refers to radio frequencies (RF) in the range of 30 kHz–300 kHz. Propagation by reflection (the actual mechanism is one of refraction) from the ionosphere is also possible. The reflection can take place at the D layer (50–90 km) or the E layer (90–150 km).


5)High frequency (HF): 3MHz and 30 MHz
radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters (ten to one hundred metres). Frequencies immediately below HF are denoted Medium-frequency (MF), and the next higher frequencies are known as Very high frequency (VHF). Since the ionosphere often refracts HF radio waves quite well (a phenomenon known as skywave propagation), this range is extensively used for medium and long range radio communication. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors:

* Sunlight/darkness at site of transmission and reception
* Transmitter/receiver proximity to terminator
* Season
* Sunspot cycle
* Solar activity
* Polar aurora

6) VHF (Very high frequency):
is the radio frequency range from 30 MHz to 300 MHz. Frequencies immediately below VHF are denoted High frequency (HF), and the next higher frequencies are known as Ultra high frequency (UHF). Common uses for VHF are FM radio broadcast, television broadcast, land mobile stations (emergency, business, and military), long range data communication with radio modems, Amateur Radio, marine communications, air traffic control communications and air navigation systems (e.g. VOR, DME & ILS).VHF propagation characteristics are ideal for short-distance terrestrial communication, with a range generally somewhat farther than line-of-sight from the transmitter (see formula below). Unlike high frequencies (HF), the ionosphere does not usually reflect VHF radio and thus transmissions are restricted to the local area (and don't interfere with transmissions thousands of kilometres away). VHF is also less affected by atmospheric noise and interference from electrical equipment than lower frequencies. Whilst it is more easily blocked by land features than HF and lower frequencies, it is less affected by buildings and other less substantial objects than UHF frequencies.