The spectrum of a signal is the range of frequencies that it contains.
The entire radio spectrum ranges in frequency from 3 kiloherdz to about 300 gigahertz.
The most crowded portion of the radio spectrum includes the bands in the lowest frequencies.
These Frequencies are ideally suited for mobile wireless communications because signalsbtraveling at these frequencies can travel further with less power than signal traveling at
ligher frequencies.
Radio waves are very long compared to the rest of the electromagnetic spectrum.
The radio spectrum is divided up into a number of 'bands' based on their wavelength and visibility for communication purpose.
The extend from the very low frequency portion of the spectrum through the Low, Medium, High, Very high, ultra high and super high to the extra high frequency range as depicted in the illustration below. Above the EHF band comes infrared radiation and then visible light.
Very Low Frequency (VLF): The VLF _region from 3_ to 30 Khz is used for both
submarine communication and for the omega navigation system.
The omega system might be considered to be a form of radar.
Low Frequency (LF): The LF region from 30 to 300 Khz, is used for some forms
of communication, and for the Loran C position—location system. At the high end of
this range are some radio beacons and weather broadcast stations used in air
navigation.
Medium Frequency (MF): The MF region, from 300 to 3000 KHz contains the
standard broadcast band from 500 to 1500 KHz, with some marine communications
remaining below the band and various communication services above it. The original
Loran a system also was just above the broadcast band at about 1.8 MHz.
High Frequency (HF): The HF region from 3 to N....Mikis used primarily for long—
distance communication and short—wave broad casting over long distances, because
this is the region most affected by reflections from the ionosphere and least affected
by absorption in the ionosphere. Because at the use of ionosphere reflection in this
region, some radar systems are operated in the HF region.
Very High Frequency (VHF): The VHF region from 30 to 300 MHz is used
primarily for television and FM broadcasting over line of sight distances and also for
communication with aircraft and other vehicles. However, some radars intended for
remote sensing have been built in this frequency range
Ultra High Frequency (UHF): The UHF region from 300 to 3000 MHz is extensively populated with radars.
Although part of it is used for television broadcasting and for mobile communications with aircraft and surface vehicles.
The radar in this region of the spectrum are normally used for aircraft detection and tracking.
Super High Frequency (SHF): The SHF ranges from 3 to 30 GHz is used for most of the remote sensing systems.
The remote sensing radars are concentrated in the region between 9 and 10 GHz and around 14 to 16 GHz.
Satellite communications use bands near 4 and 6 GHz .nd between 11 and 13 GHz as well as some higher frequencies.
Extremely High Frequency (EHF): EHF range from 30 to 300 GHz is used less extensively, although the atmospheric-window region between 30 and 40 GHz is rather widely used and applications in the neighborhood of 90 to 100 GHz are increasing because of the strong oxygen absorption in the neighbourhood of f 60 GHz.
Radars are operated for remote sensing in the 32 - 36 GHz region, and some military imaging radars are around 95 GHz.
