VLF means Very Low Frequency that extend its range from 3 to 30 KHz, corresponding to a wavelength ranging from 100 to 10 KM. They are radio waves that propagates by ground wave or by ionospheric duct, following the curvature of the earth and are capable of diffracting around obstacles and not being reflected by them. The distances reached by these radio waves are not limited by the horizon but are in the order of thousands of km. Often in this band, we listen to radio navigation services, beacons, government radio stations, and standard frequency and time signal stations. Since VLF can also propagate in the water, they are used for military communications with submarines. The modulation used in this band are mostly digital at low transmission speed, this is due to the narrow bandwidth which makes using audio modulation unthinkable.

As mentioned above, the main propagation of VLF is through a system called an ionospheric waveguide. The Earth, at a distance of 60-90 km above sea level, is surrounded by a conductive layer of electrons and ions (called Layer D), which form the Ionosphere. It has the ability to reflect radio waves in the VLF band and prevent them from dispersing into space. A "channel" is thus created between the earth's surface and the ionosphere which ensures that the VLF band radio waves remain confined within this duct or waveguide. Bouncing in a zigzag between the earth's surface and the ionosphere, radio waves undergo an attenuation of approximately 2-3 dB for every 1000 km travelled, reaching distances varying from 5,000 to 20,000 km with very stable fading but high atmospheric noise due to the interference produced by electrical discharges from lightning.

Another phenomenon that contributes to the production of radio interference in the VLF band is electron energy precipitation (EEP). This is a phenomenon that occurs when electrons coming from the solar wind and trapped in the Van Allen belts fall into the Ionosphere and collide with the ions. This occurs as a result of the propagation of VLF radio waves through the Earth's magnetic field lines. Lightning often contributes to this phenomenon (LEP) as the electrical discharge of a lightning produces an electromagnetic pulse (EMP) which strikes the electrons in the Van Allen radiation belt causing them to precipitate.