Very high frequency
As ultra-short waves ( VHF ) is referred to electromagnetic waves in a frequency range of 30 MHz to 300 MHz corresponding to wavelengths of between ten meters and one meter. They thus lie between the short-wave ( which are longer than ultra-short waves ) and the decimeter ( shorter ).
( - Very high frequency very high frequency ) used in English-speaking countries is the term for ultra-short wave VHF. The term frequency modulation (frequency modulation) is erroneously used in the broadcasting sector as a synonym and it is used the abbreviation FM.
In common parlance, the term is often used for VHF FM broadcasting in the range 87.5 to 108 MHz of the VHF band II. Among the ultra-short waves but also include the frequencies used for television stations in the broadcast bands I and III and the lower and upper special channels of cable television.
The Hyper band (Extended Special channel range) and the broadcast bands IV and V, however, belong to the decimeter.
Furthermore, the term FM is also common in the area of voice communications. It is all about the 4 m band (the frequencies below the VHF broadcasting ), the areas of the aeronautical radio with frequencies above 108 MHz, and the 2- m band in the range of 140 to 174 MHz, where many different professional services, along with an amateur band are.
The range of ultra-short waves is limited by the horizon of the electromagnetic wave propagation. This does not correspond to the optical horizon for the visible light because the refractive index of the atmosphere decreases for the FM band with the height above ground. Therefore, the curvature of the earth for the ultra-short waves appear flatter than for visible light. The so-called radio horizon is thus further away than the optical horizon. Unlike the long-, medium - and short-wave broadcasting are ultra-short radio waves, apart from the sporadic summer overreach " Sporadic - E" does not reflect off the ionosphere, so that their terrestrial range is considerably shorter. In certain weather inversions however, can lead to overreach. Depending on the transmitter and receiver location, the transmitting power and the receiving equipment is the range of an FM station of between 10 and 200 km. Therefore, a VHF transmitter network from quite a number of stations that are constructed on closely spaced, mostly on hills. In mountainous areas are often used a gap-fillers.