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84-548: As opposed to its predecessor, it featured direct-dialing (so that human operators were not required to connect calls). The frequency plan originally included only 38 channels (with one call possible per frequency channel), but it was upgraded to incorporate the A-Netz frequencies when that network was retired in 1980. The upgraded network had 78 channels and is sometimes referred to as the B2-Netz . A major limitation of system

168-471: A passive missile guidance system , which uses the emission from a target of electromagnetic radiation in the infrared part of the spectrum to track it. Missiles that use infrared seeking are often referred to as "heat-seekers" since infrared (IR) is just below the visible spectrum of light in frequency and is radiated strongly by hot bodies. Many objects such as people, vehicle engines, and aircraft generate and retain heat, and as such, are especially visible in

252-524: A thermographic camera , with the fundamental difference that each pixel contains a full LWIR spectrum. Consequently, chemical identification of the object can be performed without a need for an external light source such as the Sun or the Moon. Such cameras are typically applied for geological measurements, outdoor surveillance and UAV applications. In infrared photography , infrared filters are used to capture

336-600: A chemical and electrical process and then converted back into visible light. Infrared light sources can be used to augment the available ambient light for conversion by night vision devices, increasing in-the-dark visibility without actually using a visible light source. The use of infrared light and night vision devices should not be confused with thermal imaging , which creates images based on differences in surface temperature by detecting infrared radiation ( heat ) that emanates from objects and their surrounding environment. Infrared radiation can be used to remotely determine

420-482: A continuous sequence of weather to be studied. These infrared pictures can depict ocean eddies or vortices and map currents such as the Gulf Stream, which are valuable to the shipping industry. Fishermen and farmers are interested in knowing land and water temperatures to protect their crops against frost or increase their catch from the sea. Even El Niño phenomena can be spotted. Using color-digitized techniques,

504-563: A letter to the editor of Wireless Engineer in 1942. For example, the approximate geometric mean of band 7 is 10 MHz, or 10  Hz. The band name "tremendously low frequency" (TLF) has been used for frequencies from 1–3 Hz (wavelengths from 300,000–100,000 km), but the term has not been defined by the ITU. Frequency bands in the microwave range are designated by letters. This convention began around World War II with military designations for frequencies used in radar , which

588-403: A molecule vibrates at a frequency characteristic of that bond. A group of atoms in a molecule (e.g., CH 2 ) may have multiple modes of oscillation caused by the stretching and bending motions of the group as a whole. If an oscillation leads to a change in dipole in the molecule then it will absorb a photon that has the same frequency. The vibrational frequencies of most molecules correspond to

672-431: A more emissive one. For that reason, incorrect selection of emissivity and not accounting for environmental temperatures will give inaccurate results when using infrared cameras and pyrometers. Infrared is used in night vision equipment when there is insufficient visible light to see. Night vision devices operate through a process involving the conversion of ambient light photons into electrons that are then amplified by

756-490: A move to 2.4 GHz spread spectrum RC control systems. Licensed amateur radio operators use portions of the 6-meter band in North America. Industrial remote control of cranes or railway locomotives use assigned frequencies that vary by area. Radar applications use relatively high power pulse transmitters and sensitive receivers, so radar is operated on bands not used for other purposes. Most radar bands are in

840-463: A near-IR laser may thus appear dim red and can present a hazard since it may actually be quite bright. Even IR at wavelengths up to 1,050 nm from pulsed lasers can be seen by humans under certain conditions. A commonly used subdivision scheme is: NIR and SWIR together is sometimes called "reflected infrared", whereas MWIR and LWIR is sometimes referred to as "thermal infrared". The International Commission on Illumination (CIE) recommended

924-427: A spectrum of wavelengths, but sometimes only a limited region of the spectrum is of interest because sensors usually collect radiation only within a specific bandwidth. Thermal infrared radiation also has a maximum emission wavelength, which is inversely proportional to the absolute temperature of object, in accordance with Wien's displacement law . The infrared band is often subdivided into smaller sections, although how

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1008-407: A traditional name. For example, the term high frequency (HF) designates the wavelength range from 100 to 10 metres, corresponding to a frequency range of 3 to 30 MHz. This is just a symbol and is not related to allocation; the ITU further divides each band into subbands allocated to different services. Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere

1092-405: A worldwide scale, this cooling method has been proposed as a way to slow and even reverse global warming , with some estimates proposing a global surface area coverage of 1-2% to balance global heat fluxes. IR data transmission is also employed in short-range communication among computer peripherals and personal digital assistants . These devices usually conform to standards published by IrDA ,

1176-411: Is a property of a surface that describes how its thermal emissions deviate from the ideal of a black body . To further explain, two objects at the same physical temperature may not show the same infrared image if they have differing emissivity. For example, for any pre-set emissivity value, objects with higher emissivity will appear hotter, and those with a lower emissivity will appear cooler (assuming, as

1260-420: Is a small frequency band (a contiguous section of the range of the radio spectrum) in which channels are usually used or set aside for the same purpose. To prevent interference and allow for efficient use of the radio spectrum, similar services are allocated in bands. For example, broadcasting, mobile radio, or navigation devices, will be allocated in non-overlapping ranges of frequencies. For each radio band,

1344-451: Is absorbed then re-radiated at longer wavelengths. Visible light or ultraviolet-emitting lasers can char paper and incandescently hot objects emit visible radiation. Objects at room temperature will emit radiation concentrated mostly in the 8 to 25 μm band, but this is not distinct from the emission of visible light by incandescent objects and ultraviolet by even hotter objects (see black body and Wien's displacement law ). Heat

1428-426: Is also a technique called ' T-ray ' imaging, which is imaging using far-infrared or terahertz radiation . Lack of bright sources can make terahertz photography more challenging than most other infrared imaging techniques. Recently T-ray imaging has been of considerable interest due to a number of new developments such as terahertz time-domain spectroscopy . Infrared tracking, also known as infrared homing, refers to

1512-430: Is associated with spectra far above the infrared, extending into visible, ultraviolet, and even X-ray regions (e.g. the solar corona ). Thus, the popular association of infrared radiation with thermal radiation is only a coincidence based on typical (comparatively low) temperatures often found near the surface of planet Earth. The concept of emissivity is important in understanding the infrared emissions of objects. This

1596-537: Is being researched as an aid for visually impaired people through the Remote infrared audible signage project. Transmitting IR data from one device to another is sometimes referred to as beaming . IR is sometimes used for assistive audio as an alternative to an audio induction loop . Infrared vibrational spectroscopy (see also near-infrared spectroscopy ) is a technique that can be used to identify molecules by analysis of their constituent bonds. Each chemical bond in

1680-485: Is classified as part of optical astronomy . To form an image, the components of an infrared telescope need to be carefully shielded from heat sources, and the detectors are chilled using liquid helium . The sensitivity of Earth-based infrared telescopes is significantly limited by water vapor in the atmosphere, which absorbs a portion of the infrared radiation arriving from space outside of selected atmospheric windows . This limitation can be partially alleviated by placing

1764-423: Is counted as part of the microwave band, not infrared, moving the band edge of infrared to 0.1 mm (3 THz). Sunlight , at an effective temperature of 5,780  K (5,510 °C, 9,940 °F), is composed of near-thermal-spectrum radiation that is slightly more than half infrared. At zenith , sunlight provides an irradiance of just over 1  kW per square meter at sea level. Of this energy, 527 W

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1848-456: Is defined (according to different standards) at various values typically between 700 nm and 800 nm, but the boundary between visible and infrared light is not precisely defined. The human eye is markedly less sensitive to light above 700 nm wavelength, so longer wavelengths make insignificant contributions to scenes illuminated by common light sources. Particularly intense near-IR light (e.g., from lasers , LEDs or bright daylight with

1932-578: Is efficiently detected by inexpensive silicon photodiodes , which the receiver uses to convert the detected radiation to an electric current . That electrical signal is passed through a high-pass filter which retains the rapid pulsations due to the IR transmitter but filters out slowly changing infrared radiation from ambient light. Infrared communications are useful for indoor use in areas of high population density. IR does not penetrate walls and so does not interfere with other devices in adjoining rooms. Infrared

2016-587: Is emitted or absorbed by molecules when changing rotational-vibrational movements. It excites vibrational modes in a molecule through a change in the dipole moment , making it a useful frequency range for study of these energy states for molecules of the proper symmetry. Infrared spectroscopy examines absorption and transmission of photons in the infrared range. Infrared radiation is used in industrial, scientific, military, commercial, and medical applications. Night-vision devices using active near-infrared illumination allow people or animals to be observed without

2100-491: Is energy in transit that flows due to a temperature difference. Unlike heat transmitted by thermal conduction or thermal convection , thermal radiation can propagate through a vacuum . Thermal radiation is characterized by a particular spectrum of many wavelengths that are associated with emission from an object, due to the vibration of its molecules at a given temperature. Thermal radiation can be emitted from objects at any wavelength, and at very high temperatures such radiation

2184-552: Is especially useful since some radiation at these wavelengths can escape into space through the atmosphere's infrared window . This is how passive daytime radiative cooling (PDRC) surfaces are able to achieve sub-ambient cooling temperatures under direct solar intensity, enhancing terrestrial heat flow to outer space with zero energy consumption or pollution . PDRC surfaces maximize shortwave solar reflectance to lessen heat gain while maintaining strong longwave infrared (LWIR) thermal radiation heat transfer . When imagined on

2268-676: Is infrared radiation, 445 W is visible light, and 32 W is ultraviolet radiation. Nearly all the infrared radiation in sunlight is near infrared, shorter than 4 μm. On the surface of Earth, at far lower temperatures than the surface of the Sun, some thermal radiation consists of infrared in the mid-infrared region, much longer than in sunlight. Black-body, or thermal, radiation is continuous: it radiates at all wavelengths. Of these natural thermal radiation processes, only lightning and natural fires are hot enough to produce much visible energy, and fires produce far more infrared than visible-light energy. In general, objects emit infrared radiation across

2352-531: Is no lower limit to the frequency of radio waves. Radio waves are defined by the ITU as: "electromagnetic waves of frequencies arbitrarily lower than 3000 GHz, propagated in space without artificial guide". At the high frequency end the radio spectrum is bounded by the infrared band. The boundary between radio waves and infrared waves is defined at different frequencies in different scientific fields. The terahertz band , from 300 gigahertz to 3 terahertz, can be considered either as microwaves or infrared. It

2436-403: Is no universally accepted definition of the range of infrared radiation. Typically, it is taken to extend from the nominal red edge of the visible spectrum at 780 nm to 1 mm. This range of wavelengths corresponds to a frequency range of approximately 430 THz down to 300 GHz. Beyond infrared is the microwave portion of the electromagnetic spectrum . Increasingly, terahertz radiation

2520-457: Is often the case, that the surrounding environment is cooler than the objects being viewed). When an object has less than perfect emissivity, it obtains properties of reflectivity and/or transparency, and so the temperature of the surrounding environment is partially reflected by and/or transmitted through the object. If the object were in a hotter environment, then a lower emissivity object at the same temperature would likely appear to be hotter than

2604-530: Is one of the primary parameters studied in research into global warming , together with solar radiation . A pyrgeometer is utilized in this field of research to perform continuous outdoor measurements. This is a broadband infrared radiometer with sensitivity for infrared radiation between approximately 4.5 μm and 50 μm. Astronomers observe objects in the infrared portion of the electromagnetic spectrum using optical components, including mirrors, lenses and solid state digital detectors. For this reason it

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2688-487: Is so great that the atmosphere is effectively opaque, until it becomes transparent again in the near-infrared and optical window frequency ranges. These ITU radio bands are defined in the ITU Radio Regulations . Article 2, provision No. 2.1 states that "the radio spectrum shall be subdivided into nine frequency bands, which shall be designated by progressive whole numbers in accordance with

2772-467: Is that low clouds such as stratus or fog can have a temperature similar to the surrounding land or sea surface and do not show up. However, using the difference in brightness of the IR4 channel (10.3–11.5 μm) and the near-infrared channel (1.58–1.64 μm), low clouds can be distinguished, producing a fog satellite picture. The main advantage of infrared is that images can be produced at night, allowing

2856-519: Is that the IR energy heats only opaque objects, such as food, rather than the air around them. Infrared heating is also becoming more popular in industrial manufacturing processes, e.g. curing of coatings, forming of plastics, annealing, plastic welding, and print drying. In these applications, infrared heaters replace convection ovens and contact heating. A variety of technologies or proposed technologies take advantage of infrared emissions to cool buildings or other systems. The LWIR (8–15 μm) region

2940-824: Is the decreasing bandwidth available at low frequencies, which limits the data rate that can be transmitted. Below about 30 kHz, audio modulation is impractical and only slow baud rate data communication is used. The lowest frequencies that have been used for radio communication are around 80 Hz, in ELF submarine communications systems built by a few nations' navies to communicate with their submerged submarines hundreds of meters underwater. These employ huge ground dipole antennas 20–60 km long excited by megawatts of transmitter power, and transmit data at an extremely slow rate of about 1 bit per minute (17 millibits per second , or about 5 minutes per character). The highest frequencies useful for radio communication are limited by

3024-438: Is the dominant band for long-distance telecommunications networks . The S and L bands are based on less well established technology, and are not as widely deployed. Infrared radiation is popularly known as "heat radiation", but light and electromagnetic waves of any frequency will heat surfaces that absorb them. Infrared light from the Sun accounts for 49% of the heating of Earth, with the rest being caused by visible light that

3108-561: Is the highest band categorized as radio waves by the International Telecommunication Union . but spectroscopic scientists consider these frequencies part of the far infrared and mid infrared bands. Because it is a fixed resource, the practical limits and basic physical considerations of the radio spectrum, the frequencies which are useful for radio communication , are determined by technological limitations which are impossible to overcome. So although

3192-402: Is the most common way for remote controls to command appliances. Infrared remote control protocols like RC-5 , SIRC , are used to communicate with infrared. Free-space optical communication using infrared lasers can be a relatively inexpensive way to install a communications link in an urban area operating at up to 4 gigabit/s, compared to the cost of burying fiber optic cable, except for

3276-520: Is the spectroscopic wavenumber . It is the frequency divided by the speed of light in vacuum. In the semiconductor industry, infrared light can be used to characterize materials such as thin films and periodic trench structures. By measuring the reflectance of light from the surface of a semiconductor wafer, the index of refraction (n) and the extinction Coefficient (k) can be determined via the Forouhi–Bloomer dispersion equations . The reflectance from

3360-404: Is typically in the range 10.3–12.5 μm (IR4 and IR5 channels). Clouds with high and cold tops, such as cyclones or cumulonimbus clouds , are often displayed as red or black, lower warmer clouds such as stratus or stratocumulus are displayed as blue or grey, with intermediate clouds shaded accordingly. Hot land surfaces are shown as dark-grey or black. One disadvantage of infrared imagery

3444-555: Is used in coastal waters and relatively short-range communication between vessels and to shore stations. Radios are channelized, with different channels used for different purposes; marine Channel 16 is used for calling and emergencies. Amateur radio frequency allocations vary around the world. Several bands are common for amateurs worldwide, usually in the HF part of the spectrum. Other bands are national or regional allocations only due to differing allocations for other services, especially in

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3528-582: The ITU and the local regulating agencies like the US Federal Communications Commission (FCC) and voluntary best practices help avoid interference. As a matter of convention, the ITU divides the radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten (10 ) metres, with corresponding frequency of 3×10   hertz , and each covering a decade of frequency or wavelength. Each of these bands has

3612-543: The VHF and UHF parts of the radio spectrum. Citizens' band radio is allocated in many countries, using channelized radios in the upper HF part of the spectrum (around 27 MHz). It is used for personal, small business and hobby purposes. Other frequency allocations are used for similar services in different jurisdictions, for example UHF CB is allocated in Australia. A wide range of personal radio services exist around

3696-507: The microwave part of the spectrum, although certain important applications for meteorology make use of powerful transmitters in the UHF band. Infrared Infrared ( IR ; sometimes called infrared light ) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves . The infrared spectral band begins with waves that are just longer than those of red light (the longest waves in

3780-517: The terahertz radiation band. Almost all black-body radiation from objects near room temperature is in the IR band. As a form of electromagnetic radiation, IR carries energy and momentum , exerts radiation pressure , and has properties corresponding to both those of a wave and of a particle , the photon . It was long known that fires emit invisible heat ; in 1681 the pioneering experimenter Edme Mariotte showed that glass, though transparent to sunlight, obstructed radiant heat. In 1800

3864-426: The visible spectrum ), so IR is invisible to the human eye. IR is generally understood to include wavelengths from around 750  nm (400  THz ) to 1  mm (300  GHz ). IR is commonly divided between longer-wavelength thermal IR, emitted from terrestrial sources, and shorter-wavelength IR or near-IR, part of the solar spectrum . Longer IR wavelengths (30–100 μm) are sometimes included as part of

3948-535: The IR spectrum is thereby divided varies between different areas in which IR is employed. Infrared radiation is generally considered to begin with wavelengths longer than visible by the human eye. There is no hard wavelength limit to what is visible, as the eye's sensitivity decreases rapidly but smoothly, for wavelengths exceeding about 700 nm. Therefore wavelengths just longer than that can be seen if they are sufficiently bright, though they may still be classified as infrared according to usual definitions. Light from

4032-456: The ITU has a band plan (or frequency plan ) which dictates how it is to be used and shared, to avoid interference and to set protocol for the compatibility of transmitters and receivers . Each frequency plan defines the frequency range to be included, how channels are to be defined, and what will be carried on those channels. Typical definitions set forth in a frequency plan are: The actual authorized frequency bands are defined by

4116-488: The Infrared Data Association. Remote controls and IrDA devices use infrared light-emitting diodes (LEDs) to emit infrared radiation that may be concentrated by a lens into a beam that the user aims at the detector. The beam is modulated , i.e. switched on and off, according to a code which the receiver interprets. Usually very near-IR is used (below 800 nm) for practical reasons. This wavelength

4200-533: The VHF and UHF parts of the spectrum, are allocated for communication between fixed base stations and land mobile vehicle-mounted or portable transceivers. In the United States these services are informally known as business band radio. See also Professional mobile radio . Police radio and other public safety services such as fire departments and ambulances are generally found in the VHF and UHF parts of

4284-417: The absorption of microwave energy by the atmosphere. As frequency increases above 30 GHz (the beginning of the millimeter wave band), atmospheric gases absorb increasing amounts of power, so the power in a beam of radio waves decreases exponentially with distance from the transmitting antenna. At 30 GHz, useful communication is limited to about 1 km, but as frequency increases the range at which

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4368-502: The allocation still dedicated to television, TV-band devices use channels without local broadcasters. The Apex band in the United States was a pre-WWII allocation for VHF audio broadcasting; it was made obsolete after the introduction of FM broadcasting. Airband refers to VHF frequencies 108 to 137 MHz, used for navigation and voice communication with aircraft. Trans-oceanic aircraft also carry HF radio and satellite transceivers. The greatest incentive for development of radio

4452-521: The astronomer Sir William Herschel discovered that infrared radiation is a type of invisible radiation in the spectrum lower in energy than red light, by means of its effect on a thermometer . Slightly more than half of the energy from the Sun was eventually found, through Herschel's studies, to arrive on Earth in the form of infrared. The balance between absorbed and emitted infrared radiation has an important effect on Earth's climate . Infrared radiation

4536-539: The division of infrared radiation into the following three bands: ISO 20473 specifies the following scheme: Astronomers typically divide the infrared spectrum as follows: These divisions are not precise and can vary depending on the publication. The three regions are used for observation of different temperature ranges, and hence different environments in space. The most common photometric system used in astronomy allocates capital letters to different spectral regions according to filters used; I, J, H, and K cover

4620-522: The end of 1988, there were 1,078 participants in West Berlin alone. The network was vastly oversubscribed and finding an available channel could prove difficult. The connection between base station and handset was unencrypted , so eavesdropping was easy and common. In rare cases, additional devices were added by both participants to encrypt conversations (such as discussions of important politicians). The B-Netz would eventually be superseded by

4704-473: The eye is given a moment to adjust to the extremely dim image coming through a visually opaque IR-passing photographic filter, it is possible to see the Wood effect that consists of IR-glowing foliage. In optical communications , the part of the infrared spectrum that is used is divided into seven bands based on availability of light sources, transmitting/absorbing materials (fibers), and detectors: The C-band

4788-619: The following table". The table originated with a recommendation of the fourth CCIR meeting, held in Bucharest in 1937, and was approved by the International Radio Conference held at Atlantic City, NJ in 1947. The idea to give each band a number, in which the number is the logarithm of the approximate geometric mean of the upper and lower band limits in Hz, originated with B. C. Fleming-Williams, who suggested it in

4872-499: The frequencies of infrared light. Typically, the technique is used to study organic compounds using light radiation from the mid-infrared, 4,000–400 cm . A spectrum of all the frequencies of absorption in a sample is recorded. This can be used to gain information about the sample composition in terms of chemical groups present and also its purity (for example, a wet sample will show a broad O-H absorption around 3200 cm ). The unit for expressing radiation in this application, cm ,

4956-421: The generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU). Different parts of the radio spectrum are allocated by the ITU for different radio transmission technologies and applications; some 40 radiocommunication services are defined in the ITU's Radio Regulations (RR). In some cases, parts of

5040-537: The gray-shaded thermal images can be converted to color for easier identification of desired information. The main water vapour channel at 6.40 to 7.08 μm can be imaged by some weather satellites and shows the amount of moisture in the atmosphere. In the field of climatology, atmospheric infrared radiation is monitored to detect trends in the energy exchange between the Earth and the atmosphere. These trends provide information on long-term changes in Earth's climate. It

5124-411: The infrared light can also be used to determine the critical dimension, depth, and sidewall angle of high aspect ratio trench structures. Weather satellites equipped with scanning radiometers produce thermal or infrared images, which can then enable a trained analyst to determine cloud heights and types, to calculate land and surface water temperatures, and to locate ocean surface features. The scanning

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5208-496: The infrared range of the electromagnetic spectrum (roughly 9,000–14,000 nm or 9–14 μm) and produce images of that radiation. Since infrared radiation is emitted by all objects based on their temperatures, according to the black-body radiation law, thermography makes it possible to "see" one's environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature, therefore thermography allows one to see variations in temperature (hence

5292-412: The infrared wavelengths of light compared to objects in the background. Infrared radiation can be used as a deliberate heating source. For example, it is used in infrared saunas to heat the occupants. It may also be used in other heating applications, such as to remove ice from the wings of aircraft (de-icing). Infrared radiation is used in cooking, known as broiling or grilling . One energy advantage

5376-455: The largest use of these bands has been by short-range low-power communications systems, since users do not have to hold a radio operator's license. Cordless telephones , wireless computer networks , Bluetooth devices, and garage door openers all use the ISM bands. ISM devices do not have regulatory protection against interference from other users of the band. Bands of frequencies, especially in

5460-438: The name). A hyperspectral image is a "picture" containing continuous spectrum through a wide spectral range at each pixel. Hyperspectral imaging is gaining importance in the field of applied spectroscopy particularly with NIR, SWIR, MWIR, and LWIR spectral regions. Typical applications include biological, mineralogical, defence, and industrial measurements. Thermal infrared hyperspectral imaging can be similarly performed using

5544-405: The near-infrared spectrum. Digital cameras often use infrared blockers . Cheaper digital cameras and camera phones have less effective filters and can view intense near-infrared, appearing as a bright purple-white color. This is especially pronounced when taking pictures of subjects near IR-bright areas (such as near a lamp), where the resulting infrared interference can wash out the image. There

5628-446: The near-infrared wavelengths; L, M, N, and Q refer to the mid-infrared region. These letters are commonly understood in reference to atmospheric windows and appear, for instance, in the titles of many papers . A third scheme divides up the band based on the response of various detectors: Near-infrared is the region closest in wavelength to the radiation detectable by the human eye. mid- and far-infrared are progressively further from

5712-453: The need to utilize it more effectively is driving modern telecommunications innovations such as trunked radio systems , spread spectrum , ultra-wideband , frequency reuse , dynamic spectrum management , frequency pooling, and cognitive radio . The frequency boundaries of the radio spectrum are a matter of convention in physics and are somewhat arbitrary. Since radio waves are the lowest frequency category of electromagnetic waves , there

5796-431: The observer being detected. Infrared astronomy uses sensor-equipped telescopes to penetrate dusty regions of space such as molecular clouds , to detect objects such as planets , and to view highly red-shifted objects from the early days of the universe . Infrared thermal-imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, to assist firefighting, and to detect

5880-506: The overheating of electrical components. Military and civilian applications include target acquisition , surveillance , night vision , homing , and tracking. Humans at normal body temperature radiate chiefly at wavelengths around 10 μm. Non-military uses include thermal efficiency analysis, environmental monitoring, industrial facility inspections, detection of grow-ops , remote temperature sensing, short-range wireless communication , spectroscopy , and weather forecasting . There

5964-426: The radiation damage. "Since the eye cannot detect IR, blinking or closing the eyes to help prevent or reduce damage may not happen." Infrared lasers are used to provide the light for optical fiber communications systems. Wavelengths around 1,330 nm (least dispersion ) or 1,550 nm (best transmission) are the best choices for standard silica fibers. IR data transmission of audio versions of printed signs

6048-466: The radio spectrum are sold or licensed to operators of private radio transmission services (for example, cellular telephone operators or broadcast television stations). Ranges of allocated frequencies are often referred to by their provisioned use (for example, cellular spectrum or television spectrum). Because it is a fixed resource which is in demand by an increasing number of users, the radio spectrum has become increasingly congested in recent decades, and

6132-595: The radio spectrum is becoming increasingly congested, there is no possible way to add additional frequency bandwidth outside of that currently in use. The lowest frequencies used for radio communication are limited by the increasing size of transmitting antennas required. The size of antenna required to radiate radio power efficiently increases in proportion to wavelength or inversely with frequency. Below about 10 kHz (a wavelength of 30 km), elevated wire antennas kilometers in diameter are required, so very few radio systems use frequencies below this. A second limit

6216-595: The spectrum. Trunking systems are often used to make most efficient use of the limited number of frequencies available. The demand for mobile telephone service has led to large blocks of radio spectrum allocated to cellular frequencies . Reliable radio control uses bands dedicated to the purpose. Radio-controlled toys may use portions of unlicensed spectrum in the 27 MHz or 49 MHz bands, but more costly aircraft, boat, or land vehicle models use dedicated radio control frequencies near 72 MHz to avoid interference by unlicensed uses. The 21st century has seen

6300-548: The technically superior C-Netz , which was put into operation on May 1, 1985. This article related to telecommunications is a stub . You can help Misplaced Pages by expanding it . Frequency plan The radio spectrum is the part of the electromagnetic spectrum with frequencies from 3  Hz to 3,000  GHz (3  THz ). Electromagnetic waves in this frequency range, called radio waves , are widely used in modern technology, particularly in telecommunication . To prevent interference between different users,

6384-479: The temperature of objects (if the emissivity is known). This is termed thermography, or in the case of very hot objects in the NIR or visible it is termed pyrometry . Thermography (thermal imaging) is mainly used in military and industrial applications but the technology is reaching the public market in the form of infrared cameras on cars due to greatly reduced production costs. Thermographic cameras detect radiation in

6468-464: The term has not been defined by the ITU. Broadcast frequencies: Designations for television and FM radio broadcast frequencies vary between countries, see Television channel frequencies and FM broadcast band . Since VHF and UHF frequencies are desirable for many uses in urban areas, in North America some parts of the former television broadcasting band have been reassigned to cellular phone and various land mobile communications systems. Even within

6552-476: The visible light filtered out) can be detected up to approximately 780 nm, and will be perceived as red light. Intense light sources providing wavelengths as long as 1,050 nm can be seen as a dull red glow, causing some difficulty in near-IR illumination of scenes in the dark (usually this practical problem is solved by indirect illumination). Leaves are particularly bright in the near IR, and if all visible light leaks from around an IR-filter are blocked, and

6636-472: The visible spectrum. Other definitions follow different physical mechanisms (emission peaks, vs. bands, water absorption) and the newest follow technical reasons (the common silicon detectors are sensitive to about 1,050 nm, while InGaAs 's sensitivity starts around 950 nm and ends between 1,700 and 2,600 nm, depending on the specific configuration). No international standards for these specifications are currently available. The onset of infrared

6720-468: The waves can be received decreases. In the terahertz band above 300 GHz, the radio waves are attenuated to zero within a few meters due to the absorption of electromagnetic radiation by the atmosphere (mainly due to ozone , water vapor and carbon dioxide ), which is so great that it is essentially opaque to electromagnetic emissions, until it becomes transparent again near the near-infrared and optical window frequency ranges. A radio band

6804-422: The world, usually emphasizing short-range communication between individuals or for small businesses, simplified license requirements or in some countries covered by a class license, and usually FM transceivers using around 1 watt or less. The ISM bands were initially reserved for non-communications uses of RF energy, such as microwave ovens , radio-frequency heating, and similar purposes. However, in recent years

6888-531: Was that, in order to reach a subscriber, one had to know his location since the handset would assume the local area code of the base station serving it. Handoff was not possible and calls were dropped when cells were switched. Roaming was possible between the implementing countries. At its height in 1986, the network had 158 base stations and about 27,000 subscribers in Germany and 1,770 in Austria . At

6972-620: Was the first application of microwaves. There are several incompatible naming systems for microwave bands, and even within a given system the exact frequency range designated by a letter may vary somewhat between different application areas. One widely used standard is the IEEE radar bands established by the US Institute of Electrical and Electronics Engineers . The band name "tremendously low frequency" (TLF) has been used for frequencies from 1–3  Hz (wavelengths of 300,000–100,000 km), but

7056-478: Was the need to communicate with ships out of visual range of shore. From the very early days of radio, large oceangoing vessels carried powerful long-wave and medium-wave transmitters. High-frequency allocations are still designated for ships, although satellite systems have taken over some of the safety applications previously served by 500 kHz and other frequencies. 2182 kHz is a medium-wave frequency still used for marine emergency communication. Marine VHF radio

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