electromagnetic spectrum - technical definition

The full range of electromagnetic energy that can be radiated, as defined by frequency (f), or wavelength , which is the inverse of frequency. In terms of frequency, the spectrum begins at almost zero (0) and extends to infinity. In terms of wavelength, the spectrum begins at almost zero and extends to infinity, but in reverse.The portion of the spectrum currently usable for telecommunications includes electricity, radio, and infrared light. Table E-4 includes frequency band designations, nominal frequency ranges, nominal wavelengths, and example telecommunications applications.

Table E-4: Frequency Spectrum: Band Designations, Nominal Frequency Ranges, Nominal Wavelengths, and Example Communications Applications

Band Designation	Frequency (Hz)1	Wavelength2	Applications
Audible	20 Hz ­ 20 kHz	>100 km	Acoustics
Extremely Low Frequency (ELF) Radio	30 Hz ­ 300 Hz	10,000 km ­ 1,000 km	Submarine Communications
Infralow Frequency (ILF)	300 Hz ­ 3 kHz	1,000 km ­ 100 km	Not Applicable
Very Low Frequency (VLF) Radio	3 kHz ­ 30 kHz	100 km ­ 10 km	Navigation, Weather
Low Frequency (LF) Radio	30 kHz ­ 300 kHz	10 km ­ 1 km	Navigation, Maritime Communications, Information and Weather Systems, Time Systems
Medium Frequency (MF) Radio	300 kHz ­ 3 MHz	1 km ­ 100 m	Navigation, AM Radio, Mobile Radio
High Frequency (HF) Radio	3 MHz ­ 30 MHz	100 ­ 10 m	Citizens Band (CB) Radio (aka Shortwave Radio), Mobile Radio, Maritime Radio
Very High Frequency (VHF) Radio	30 MHz ­ 300 MHz	10 m ­ 1 m	Amateur (Ham) Radio, VHF TV, FM Radio, Mobile Satellite, Mobile Radio, Fixed Radio
Ultra High Frequency (UHF) Radio	300 MHz ­ 3 GHz	1 m ­ 10 cm	Microwave, Satellite, UHF TV, Paging, Cordless Telephony, Cellular and PCS Telephony, Wireless LAN
Super High Frequency (SHF) Radio	3 GHz ­ 30 GHz	10 cm ­ 1 cm	Microwave, Satellite, Wireless LAN
Extremely High Frequency (EHF) Radio	30 GHz ­ 300 GHz	1 cm ­ 1 mm	Microwave, Satellite, Radiolocation
Infrared Light (IR)	300 GHz ­ 400 THz	1 mm ­ 750 nm	Wireless LAN Bridges, Wireless LANs, Fiber Optics
Visible Light	400 THz ­ 1 PHz	750 nm ­ 380 nm	Not Applicable
Ultraviolet Light (UV)	1 PHz ­ 30 PHz	380 nm ­ 10 nm	Not Applicable
X-Rays	30 PHz ­ 30 EHz	10 nm ­ .01 nm	Not Applicable
Gamma and Cosmic Rays	>3 EHz	<.1 nm	Not Applicable

1 k = kilo = 1,000 (1 thousand) 1 M = Mega = 1,000,000 (1 million) 1 G = Giga = 1,000,000,000 (1 billion) 1 T = Tera = 1,000,000,000,000 (1 trillion) 1 P = Peta = 1,000,000,000,000,000 (1 quadrillion) 1 E = Exa = 1,000,000,000,000,000,000 (1 quintillion) 2 km = kilometer (1,000 meters) 2 m = meter 2 cm = centimeter (1/100 meter) 2 mm = millimeter (1/1,000 meter) 2 µ = micron (1/1,000,000 meter) 2 nm = nanometer (1/1,000,000,000 meter) The wavelength figures assume transmission in a vacuum.Wavelength in a medium will be shorter due to the fact that the frequency remains the same while the signal propagates at speeds less than 300 km/s. For example, in glass the speed of light is reduced by the index of refraction, which is about 1.5 in practice, so the velocity of propagation (Vp) is approximately 200 km/s (300/1.5 = 200). Index of refraction (IOR) is the ratio of speed in a vacuum divided by speed in the medium. See also IOR, medium, vacuum, and Vp.