Electromagnetic spectrum

Overview
The electromagnetic spectrum is a collective term; referring to the entire range and scope of frequencies of electromagnetic radiation and their respective, associated photon wavelengths. It is the range of all the possible frequencies of known electromagnetic radiation (EM radiation or EMR), which is ultimately a form of radiant energy released by certain electromagnetic processes. Light, microwaves, X-rays, gamma- rays, T-rays, television emergency beacon signals, satellite communications, radar and radio waves are all part of it.

The electromagnetic spectrum extends from below the low frequencies used for modern radio communication to gamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands of kilometers down to a fraction of the size of an atom. Visible light lies toward the shorter end, with wavelengths from 400 to 700 nanometres. The limit for long wavelengths is the size of the universe itself, while it is thought that the short wavelength limit is in the vicinity of the Planck length. Until the middle of the 20th century it was believed by most physicists that this spectrum was infinite and continuous.

Nearly all types of electromagnetic radiation can be used for spectroscopy, to study and characterize matter. Other technological uses are described under electromagnetic radiation.

Extremely low frequency



 * Frequency range- 3 to 30 Hz.
 * Wavelength range- 100,000 to 10,000 km, respectively.

Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively. In atmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz. In the related magnetosphere science, the lower frequency electromagnetic oscillations (pulsations occurring below ~3 Hz) are considered to lie in the ULF range, which is thus also defined differently from the ITU radio bands.

ELF radio waves are generated by lightning and natural disturbances in Earth's magnetic field, so they are a subject of research by atmospheric scientists. Because of the difficulty of building antennas that can radiate such long waves, ELF frequencies have been used in only a very few human-made communication systems. ELF waves can penetrate seawater, which makes them useful in communication with submarines. The US, Russia, and India are the only nations known to have constructed ELF communication facilities. The U.S. facilities were used between 1985 and 2004 but are now decommissioned. ELF waves can also penetrate significant distances into earth or rock, and "through-the-earth" underground mine communication systems use frequencies of 300 to 3000 Hz. The frequency of alternating current flowing in electric power grids, 50 or 60 Hz, also falls within the ELF band, making power grids an unintentional source of ELF radiation.

Super low frequency

 * Frequency range- 30 to 300 Hz
 * Wavelength range- 10,000 to 1,000 km

Super low frequency (SLF) is electromagnetic waves (radio waves) in the frequency range between 30 hertz and 300 hertz. They have corresponding wavelengths of 10,000 to 1,000 kilometers. This frequency range includes the frequencies of AC power grids (50 hertz and 60 hertz). Another conflicting designation which includes this frequency range is Extremely Low Frequency (ELF), which in some contexts refers to all frequencies up to 300 hertz.

Because of the extreme difficulty of building transmitters that can generate such long waves, frequencies in this range have been used in very few artificial communication systems. However, SLF waves can penetrate seawater to a depth of hundreds of meters. Therefore, in recent decades the U.S., Russian and Indian military have built huge radio transmitters using SLF frequencies to communicate with their submarines. The U.S. naval service is called Seafarer and operates at 76 hertz. It became operational in 1989 but was discontinued in 2004 due to advances in VLF communication systems. The Russian service is called ZEVS and operates at 82 hertz. The Indian Navy has an operational ELF communication facility at the INS Kattabomman naval base to communicate with its Arihant class and Akula class submarines.

The requirements for receivers at SLF frequencies is less stringent than transmitters, because the signal strength (set by atmospheric noise) is far above the noise floor of the receiver, so small, inefficient antennas can be used. Radio amateurs have received signals in this range using simple receivers built around personal computers, with coil or loop antennas connected to the PCs sound card. Signals are analysed by a software fast Fourier transform algorithm and converted into audible sound.

Ultra low frequency

 * Frequency range- 0.3 to 3 kHz
 * Wavelength range- 1,000 to 100 km

Ultra low frequency (ULF) is the ITU designation for the frequency range of electromagnetic waves between 300 hertz and 3 kilohertz. In magnetosphere science and seismology, alternative definitions are usually given, including ranges from 1 mHz to 100 Hz, 1 mHz to 1 Hz, 10 mHz to 10 Hz. Frequencies above 3 Hz in atmosphere science are usually assigned to the ELF range.

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 Alfvén 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.

Very low frequency



 * Frequency range- 3 to 30 kHz
 * Wavelength range- 100 to 10 km

Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3 kHz to 30 kHz and corresponding wavelengths from 100 to 10 kilometres, respectively. The band is also known as the myriametre band or myriametre wave as the wavelengths range from one to ten myriametres (an obsolete metric unit equal to 10 kilometres). Due to its limited bandwidth, audio (voice) transmission is highly impractical in this band, and therefore only low data rate coded signals are used. The VLF band is used for a few radio navigation services, government time radio stations (broadcasting time signals to set radio clocks) and for secure military communication. Since VLF waves can penetrate at least 40 meters (120 ft) into saltwater, they are used for military communication with submarines.

Low frequency



 * Frequency range- 30 to 300 kHz.
 * Wavelength range- 10 to 1 km.

Low frequency (low freq) or LF is the ITU designation for radio frequencies (RF) in the range of 30 kHz–300 kHz. As its wavelengths range from ten kilometres to one kilometre, respectively, it is also known as the kilometre band or kilometre wave.

LF radio waves exhibit low signal attenuation, making them suitable for long-distance communications. In Europe and areas of Northern Africa and Asia, part of the LF spectrum is used for AM broadcasting as the "longwave" band. In the western hemisphere, its main use is for aircraft beacon, navigation (LORAN), information, and weather systems. A number of time signal broadcasts are also broadcast in this band.

Medium frequency



 * Frequency range- 0.3 to 3 MHz.
 * Wavelength range- 1000 to 100 m.

Medium frequency (MF) is the ITU designation for radio frequencies (RF) in the range of 300 kHz to 3 MHz. Part of this band is the medium wave (MW) AM broadcast band. The MF band is also known as the hectometer band or hectometer wave as the wavelengths range from ten to one hectometer (1,000 to 100 m). Frequencies immediately below MF are denoted low frequency (LF), while the first band of higher frequencies is known as high frequency (HF). MF is mostly used for AM radio broadcasting, navigational radio beacons, maritime ship-to-shore communication, and transoceanic air traffic control.

High frequency



 * Frequency range- 3 to 30 MHz.
 * Wavelength range- 100 to 10 m.

High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 MHz. It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters (ten to one hundred metres). Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances. The band is used by international shortwave broadcasting stations (2.31–25.82 MHz), aviation communication, government time stations, weather stations, amateur radio and citizens band services, among other uses.

Very high frequency



 * Frequency range- 30 MHz to 300 MHz.
 * Wavelength range- 10 to 1 m.

Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 MHz to 300 MHz, with corresponding wavelengths of ten to one meters. 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 broadcasting, television broadcasting, two way land mobile radio systems (emergency, business, private use and military), long range data communication up to several tens of kilometres with radio modems, amateur radio, and marine communications. Air traffic control communications and air navigation systems (e.g. VOR & ILS) work at distances of 100 kilometres or more to aircraft at cruising altitude.

VHF was used for analog television stations in the US, and continues to be used for digital television as well as in Europe but in the latter only Band III is used even though originally Band I was planned to be used. Some older DVB-T receivers included channels E2 to E4 but newer ones only go down to channel E5.

Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 MHz to 300 MHz, with corresponding wavelengths of ten to one meters. 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 broadcasting, television broadcasting, two way land mobile radio systems (emergency, business, private use and military), long range data communication up to several tens of kilometres with radio modems, amateur radio, and marine communications. Air traffic control communications and air navigation systems (e.g. VOR & ILS) work at distances of 100 kilometres or more to aircraft at cruising altitude.

VHF was used for analog television stations in the US, and continues to be used for digital television as well as in Europe but in the latter only Band III is used even though originally Band I was planned to be used. Some older DVB-T receivers included channels E2 to E4 but newer ones only go down to channel E5.

Ultra high frequency



 * Frequency range- 300 MHz to 3 GHz.
 * Wavelength range- 1 m to 1 dm.

Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 MHz and 3 GHz, also known as the decimetre band as the wavelengths range from one meter to one decimeter. Radio waves with frequencies above the UHF band fall into the SHF (super-high frequency) or microwave frequency range. Lower frequency signals fall into the VHF (very high frequency) or lower bands. UHF radio waves propagate mainly by line of sight; they are blocked by hills and large buildings although the transmission through building walls is strong enough for indoor reception. They are used for television broadcasting, cell phones, satellite communication including GPS, personal radio services including Wi-Fi and Bluetooth, walkie-talkies, cordless phones, and numerous other applications.

The IEEE defines the UHF radar band as frequencies between 300 MHz and 1 GHz. Two other IEEE radar bands overlap the ITU UHF band: the L band between 1 and 2 GHz and the S band between 2 and 4 GHz.

Super high frequency



 * Frequency range- 3 to 30 GHz.
 * Wavelength range- 1 dm to 1 cm.

Super high frequency (SHF) is the ITU designation for radio frequencies (RF) in the range between 3 GHz and 30 GHz. This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from one to ten centimetres. These frequencies fall within the microwave band, so radio waves with these frequencies are called microwaves. The small wavelength of microwaves allows them to be directed in narrow beams by aperture antennas such as parabolic dishes, so they are used for point-to-point communication and data links and for radar. This frequency range is used for most radar transmitters, wireless LANs, satellite communication, microwave radio relay links, and numerous short range terrestrial data links. Wireless USB technology is anticipated to use approximately one-third of this spectrum.[citation needed]

Frequencies in the SHF range are often referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations.

Extremely high frequency



 * Frequency range- 30 to 300 GHz.
 * Wavelength range- 1 cm to 1 mm.

Extremely high frequency (EHF) is the International Telecommunications Union (ITU) designation for the band of radio frequencies in the electromagnetic spectrum from 30 to 300 gigahertz. It lies between the super high frequency band, and the far infrared band which is also referred to as the terahertz gap. Radio waves in this band have wavelengths from ten to one millimetre, giving it the name millimetre band or millimetre wave, sometimes abbreviated MMW or mmW. Millimetre-length electromagnetic waves were first investigated in the 1890s by Indian scientist Jagadish Chandra Bose.

Compared to lower bands, radio waves in this band have high atmospheric attenuation; they are absorbed by the gases in the atmosphere. Therefore, they have a short range and can only be used for terrestrial communication over about a kilometer. Absorption by humidity in the atmosphere is significant except in desert environments, and attenuation by rain (rain fade) is a serious problem even over short distances. However the short propagation range allows smaller frequency reuse distances than lower frequencies. The short wavelength allows modest size antennas to have a small beam width, further increasing frequency reuse potential.

Traffic police use speed-detecting radar guns in the Ka-band (33.4 – 36.0 GHz).

Tremendously high frequency



 * Frequency range- 300 GHz to 3 THz.
 * Wavelength range- 1 mm to 100 μm.

Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency, T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the ITU-designated band of frequencies from 0.3 to 3 terahertz (THz; 1 THz = 1012 Hz). Wavelengths of radiation in the terahertz band correspondingly range from 1 mm to 0.1 mm (or 100 μm). Because terahertz radiation begins at a wavelength of one millimeter and proceeds into shorter wavelengths, it is sometimes known as the submillimeter band, and its radiation as submillimeter waves, especially in astronomy.

Terahertz radiation occupies a middle ground between microwaves and infrared light waves known as the terahertz gap, where technology for its generation and manipulation is in its infancy. It represents the region in the electromagnetic spectrum where the frequency of electromagnetic radiation becomes too high to be measured digitally via electronic counters, so must be measured by proxy using the properties of wavelength and energy. Similarly, the generation and modulation of coherent electromagnetic signals in this frequency range ceases to be possible by the conventional electronic devices used to generate radio waves and microwaves, requiring the development of new devices and techniques. Photon energy in the THz regime is less than the band-gap energy of nonmetallic materials and thus THz radiation can penetrate such materials. THz beams transmitted through materials can be used for material characterization, layer inspection and as an alternative to X-rays for producing high resolution images of the interior of solid objects.

Arial size
The longer the wave length, the longer the aerial. TV aerials are thus smaller then navy aerials fore radioing subs. A civil radio aerial is between the two.

Modern SPOT satellite imaging uses
The SPOT 6 and SPOT 7 satellites are phased in the same orbit as Pléiades 1A and Pléiades 1B at an altitude of 694 km, forming a constellation of 2-by-2 satellites - 90° apart from one another.
 * Image product resolution:
 * Panchromatic: 1.5 m.
 * Colour merge: 1.5 m.
 * Multi-spectral: 6 m.
 * Spectral bands, with simultaneous panchromatic and multi-spectral acquisitions:
 * Panchromatic (450 – 745 nm).
 * Blue (450 – 525 nm).
 * Green (530 – 590 nm).
 * Red (625 – 695 nm).
 * Near-infrared (760 – 890 nm).
 * Other image data.
 * Footprint: 60 km × 60 km.
 * Responsive satellite tasking, with six tasking plans per day, per satellite.
 * Capacity to acquire up to 3 million km2 daily.

Also see



 * 1) RAF Fylingdales
 * 2) The DEW Line
 * 3) Radar
 * 4) AN/FPS-108 Cobra Dane radar
 * 5) Thule Air Base, Greenland
 * 6) AEW&C
 * 7) Boeing RC-135 Cobra Ball
 * 8) Cold War radio jamming
 * 9) XTAR
 * 10) EMP
 * 11) TV
 * 12) Microwave ovens
 * 13) Electromagnetic Pulse (EMP)
 * 14) POMCUS sites
 * 15) Nuclear fallout
 * 16) Nukes
 * 17) Radome
 * 18) Blue Vixen Radar
 * 19) Ferranti Blue Fox Radar
 * 20) Westinghouse AN/APG-66 fire-control radar
 * 21) Telecommunications
 * 22) Radio

Relevant technical terminology Source

 * 1) Frequency
 * 2) fe
 * 3) Ultra low frequency
 * 4) Super_low_frequency
 * 5) Very_low_frequency
 * 6) Radio_wave
 * 7) Nanometre
 * 8) X-ray
 * 9) Mm
 * 10) Hz
 * 11) Microwave
 * 12) ne
 * 13) eV
 * 14) Wave- length
 * 15) Low_frequency
 * 16) km
 * 17) μm
 * 18) infrared
 * 19) THz
 * 20) me
 * 21) Extremely_high_frequency
 * 22) GHz
 * 23) Far infrared
 * 24) Super_high_frequency
 * 25) Ultra_high_frequency
 * 26) Very_high_frequency
 * 27) μe
 * 28) dm
 * 29) mm
 * 30) cm
 * 31) High_frequency
 * 32) m
 * 33) Medium_frequency
 * 34) /Kilohertz
 * 35) Ionizing radiation
 * 36) MHz
 * 37) Pico-
 * 38) Energy
 * 39) Visible
 * 40) Extremely_low_frequency
 * 41) Near_ultraviolet
 * 42) EHz
 * 43) pm
 * 44) Me
 * 45) ke
 * 46) X-rays
 * 47) Gamma rays
 * 48) Extreme ultraviolet
 * 49) PHz