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Physics_in_Action_Electromagnetic_Spectrum_S32LS06

Physics in Action Electromagnetic Spectrum S32LS06

Physics in Action, The 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.

Overview as tables

Table 1

Class. Frequency. Wavelength. Energy.
X and Gamma rays are Ionising. 300 EHz pm 1.24 MeV
γ Gamma rays
30 EHz 10 pm 124 keV
HX Hard X-rays
3 EHz 100 pm 12.4 keV
SX Soft X-rays
300 PHz nm 1.24 keV
30 PHz 10 nm 124 eV
EUV Extreme

ultraviolet

3 PHz 100 nm 12.4 eV
NUV Near_ultraviolet
Visible 300 THz μm 1.24 eV
NIR Near Infrared
30 THz 10 μm 124 meV
MIR Mid infrared
3 THz 100 μm 12.4 meV
FIR Far infrared
300 GHz mm 1.24 meV

Radio_waves (8-12 GHz for I and  X band radars).

EHF Extremely_high_frequency
30 GHz cm 124 μeV
SHF Super_high_frequency
3 GHz dm 12.4 μeV
UHF Ultra_high_frequency
300 MHz m 1.24 μeV
VHF Very_high_frequency
30 MHz 10 m 124 neV
HF High_frequency
3 MHz 100 m 12.4 neV
MF Medium_frequency
300 kHz km 1.24 neV
LF Low_frequency
30 kHz 10 km 124 peV
VLF Very_low_frequency
3 kHz 100 km 12.4 peV
VF / ULF Voice_frequency
300 Hz Mm 1.24 peV
SLF Super_low_frequency
30 Hz 10 Mm 124 feV
ELF Extremely_low_frequency
3 Hz 100 Mm 12.4 feV

Table 2

Band name. Abbreviation. ITU band. Frequency

and wavelength in air.

Example uses.
Tremendously low frequency TLF < 3 Hz

> 100,000 km

Natural and artificial electromagnetic noise and brain waves (1Hz).
Extremely low frequency ELF 3–30 Hz

100,000 km – 10,000 km

Communication with submarines
Super low frequency SLF 30–300 Hz

10,000 km – 1000 km

Communication with submarines
Ultra low frequency ULF 300–3000 Hz

1000 km – 100 km

Submarine communication, communication within mines
Very low frequency VLF 4 3–30 kHz

100 km – 10 km

Navigationtime signals, submarine communication, wireless heart rate monitorsgeophysics
Low frequency LF 5 30–300 kHz

10 km – 1 km

Navigation, clock time signals, AM longwave broadcasting (Europe and parts of Asia), RFID,amateur radio
Medium frequency MF 6 300–3000 kHz

1 km – 100 m

AM (medium-wave) broadcasts, amateur radio, avalanche beacons
High frequency HF 7 3–30 MHz

100 m – 10 m

Shortwave broadcasts, citizens' band radio, amateur radio and over-the-horizon aviation communications, RFIDover-the-horizon radarautomatic link establishment (ALE) / near-vertical incidence skywave (NVIS) radio communications, marine and mobile radio telephony
Very high frequency VHF 8 30–300 MHz

10 m – 1 m

FMtelevision broadcasts and line-of-sight ground-to-aircraft and aircraft-to-aircraft communications, land mobile and maritime mobile communications, amateur radio, weather radio
Ultra high frequency UHF 9 300–3000 MHz

1 m – 100 mm

Television broadcasts, microwave ovenmicrowave devices/communications, radio astronomy,mobile phoneswireless LANBluetoothZigBeeGPS and two-way radios such as land mobile,FRS and GMRS radios, amateur radio
Super high frequency SHF 10 3–30 GHz

100 mm – 10 mm

Radio astronomy, microwave devices/communications, wireless LAN, most modern radars,communications satellites, satellite television broadcasting, DBS, amateur radio
Extremely high frequency EHF 11 30–300 GHz

10 mm – 1 mm

Radio astronomy, high-frequency microwave radio relay, microwave remote sensing, amateur radio, directed-energy weaponmillimeter wave scanner
Terahertz orTremendously high frequency THz or THF 12 300–3,000 GHz

1 mm – 100 μm

Terahertz imaging – a potential replacement for X-rays in some medical applications, ultrafast molecular dynamics, condensed-matter physicsterahertz time-domain spectroscopy, terahertz computing/communications, sub-mm remote sensing, amateur radio

Radio and Microwave sub-frequencies

Lualualei_VLF_transmitter-0

Lualualei VLF transmitter-0

lualualei vlf transmitter wiki lualualei vlf transmitter vlf transmitter lualualei very low frequency lualualei vlf transmitter.

Extremely low frequency 

Clam Lake ELF

A 1982 aerial view of the U.S. Navy Clam Lake, Wisconsin ELF transmitter facility, used to communicate with deeply submerged submarines.

  • 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

File:VLFatPalmer.JPG

A VLF receiving antenna at Palmer Station, Antarctica, operated by Stanford University.

  • 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

File:Atomic clock.jpg

An LF radio clock.

  • 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

File:2008-07-28 Mast radiator.jpg

Mast radiator of a commercial MF AM broadcasting station, Chapel Hill, North Carolina, USA.

  • 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

File:ICOM IC-M700PRO.jpg

A modern Icom M700Pro two-way radio for marine HF radio communications.

  • 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

File:Antenna.jpg

VHF television antennas used for broadcast television reception. These six antennas are a type known as a Yagi antenna, which is widely used at VHF.

  • 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

UHF TV Antenna 001

UHF television antenna on a residence. This type of antenna, called a Yagi-Uda antenna, is widely used at UHF frequencies.

File:Reflective array, bow tie, grid, or panel UHF television antenna,.jpg

Another antenna type common at UHF; a reflective array TV antenna consisting of two high-bandwidth "bow tie" dipoles in front of a flat reflector screen. The antenna is oriented so as to receive vertically-polarized radio waves, while most UHF TV stations transmit horizontally polarized waves.

File:Binatone MR 200 radio 1.jpg

Walkie talkies which operate on the 446 MHz PMR (Professional Mobile Radio) band. The 67 cm wavelength permits them to use very short "Rubber Ducky" antennas.

  • 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

File:Parabolic antennas.JPG

A variety of parabolic antennas on a communications tower in Australia for point-to-point microwave communication links. Some have white plastic radomes over their apertures to protect against rain.

Radar antennas on USS Theodore Roosevelt SPS-64

A X-band (8 - 12 GHz) marine radar antenna on a ship. The rotating bar sweeps a vertical fan-shaped beam of microwaves around the water surface to the horizon, detecting nearby ships and other obstructions

  • 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 

File:The Atacama Compact Array.jpg

Part of the Atacama Large Millimeter Array (ALMA) a millimeter wave radio telescope being built in Chile.

File:CableFree MMW Link installed in UAE.jpg

CableFree MMW link installed in the UAE installed for Safe City applications, providing 1Gbit/s capacity between sites. The links are fast to deploy, flexible and lower cost than fibre optics.

File:Minsk port bow AK-630 CIWS gun fire control radar.JPG

Millimeter wave fire control radar for CIWS gun on Russian aircraft carrier Minsk.

  • 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

Spectre Terahertz

Terahertz waves lie at the far end of the infrared band, just before the start of the microwave band.

File:Processing of low resolution THz images.png

Fine features are revealed by the THz image: THz image, after being processed, gives the same features as X-ray does.

File:Optical, THz and X-ray Images.png

(a) Optical image of an electronic chip. (b) Terahertz transmission image of the chip. (c) X-ray transmission image of the chip. Terahertz has the privilege of being non-ionizing (non-destructive) but the resolution of X-ray is higher.

  • 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.

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

All_About_the_Electromagnetic_Spectrum

All About the Electromagnetic Spectrum

All About the Electromagnetic Spectrum. How can you see the unseen through a thermal imaging camera?

  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. Radom
  18. Blue Vixen Radar
  19. Ferranti Blue Fox Radar
  20. Westinghouse AN/APG-66 fire-control radar
  21. Telecommunications
  22. Radio

Exsternal links

  1. https://www.researchgate.net/publication/303563271_Developing_terahertz_imaging_equation_and_enhancement_of_the_resolution_of_terahertz_images_using_deconvolution
  2. https://www.researchgate.net/publication/283517706_Impact_of_Mobile_Phone_Electromagnetic_Waves_on_Brainwaves
  3. https://books.google.com/books?id=4LtmjGNwOPIC&pg=PA57&dq=cross+polarization+discrimination
  4. http://en.wikipedia.org/wiki/Radio_spectrum
  5. http://en.wikipedia.org/wiki/Electromagnetic_spectrum
  6. http://en.wikipedia.org/wiki/X_band
  7. http://en.wikipedia.org/wiki/Radar
  8. http://www.flightradar24.com/
  9. http://en.wikipedia.org/wiki/I_band
  10. http://www.bom.gov.au/australia/radar/
  11. http://www.accuweather.com/en/us/national/weather-radar
  12. http://www.intellicast.com/National/Radar/Current.aspx
  13. http://radaronline.com/
  14. http://en.wikipedia.org/wiki/Electromagnetic_radiation
  15. https://directory.eoportal.org/web/eoportal/satellite-missions/p/pleiades
  16. https://en.wikipedia.org/wiki/SPOT_(satellite)
  17. https://en.wikipedia.org/wiki/List_of_2.4_GHz_radio_use
  18. https://en.wikipedia.org/wiki/ISM_band
  19. https://www.wired.com/2010/09/wireless-explainer/
  20. http://www.securitycamera2000.com/categories/Wireless-Devices/TX-%7B47%7D-RX-Kits/2.4GHz-Frequency/
  21. http://acma.gov.au/theACMA/spectrum-at-434-mhz-for-low-powered-devices
  22. http://www.linksys.com/us/support-article?articleNum=134478
  23. http://www.jneuhaus.com/fccindex/2_3_ghz.html
  24. http://www.lightreading.com/mobile/5g/eurobites-ofcom-imposes-5g-spectrum-auction-caps/d/d-id/734448?piddl_msgorder=asc
  25. http://copradar.com/preview/chapt7/ch7d1.html
  26. https://en.wikipedia.org/wiki/Terahertz_radiation#Communication
  27. https://en.wikipedia.org/wiki/Super_high_frequency
  28. https://en.wikipedia.org/wiki/Extremely_high_frequency
  29. https://en.wikipedia.org/wiki/Ultra_high_frequency
  30. https://en.wikipedia.org/wiki/Very_high_frequency
  31. https://en.wikipedia.org/wiki/High_frequency
  32. https://en.wikipedia.org/wiki/Medium_frequency
  33. https://en.wikipedia.org/wiki/Low_frequency
  34. https://en.wikipedia.org/wiki/Very_low_frequency
  35. https://en.wikipedia.org/wiki/Ultra_low_frequency
  36. https://en.wikipedia.org/wiki/Super_low_frequency
  37. https://en.wikipedia.org/wiki/Extremely_low_frequency
  38. https://en.wikipedia.org/wiki/Electromagnetic_spectrum
  39. http://edition.cnn.com/2017/07/17/politics/us-navy-drone-laser-weapon/index.html?CNNPolitics=Tw
  40. https://www.yahoo.com/news/space-corps-military-branch-approved-184442777.html
  41. https://www.yahoo.com/news/us-navy-tests-laser-weapon-125916394.html
  42. https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html
  43. https://images.search.yahoo.com/search/images;_ylt=A0LEV0IJbXJZTq0A.B9XNyoA;_ylu=X3oDMTByMDgyYjJiBGNvbG8DYmYxBHBvcwMyBHZ0aWQDBHNlYwNzYw--?p=Electromagnetic+spectrum&fr=yset_chr_cnewtab