The 6-meter band is the lowest portion of the very high frequency (VHF) radio spectrum (50.000-54.000 MHz) internationally allocated to amateur radio use. The term refers to the average signal wavelength of 6 meters.
90-610: Although located in the lower portion of the VHF band, it nonetheless occasionally displays propagation mechanisms characteristic of the high frequency (HF) bands. This normally occurs close to sunspot maximum, when solar activity increases ionization levels in the upper atmosphere. Worldwide 6 meter propagation occurred during the sunspot maximum of 2005, making 6 meter communications as good as or, in some cases and locations, better than HF frequencies. The prevalence of HF characteristics on this VHF band has inspired amateur operators to dub it
180-477: A function of frequency , distance and other conditions. A single model is usually developed to predict the behavior of propagation for all similar links under similar constraints. Created with the goal of formalizing the way radio waves are propagated from one place to another, such models typically predict the path loss along a link or the effective coverage area of a transmitter . The inventor of radio communication, Guglielmo Marconi , before 1900 formulated
270-471: A band's article for specifics. [ w ] HF allocation created at the 1979 World Administrative Radio Conference . These are commonly called the " WARC bands ". [ x ] This is not mentioned in the ITU 's Table of Frequency Allocations , but many individual administrations have commonly adopted this allocation under "Article 4.4" . [ y ] This includes a currently active footnote allocation mentioned in
360-607: A bandwidth of less than 60 Hz. The Report and Order also allows the use of modes that comply with emission designator “2K80J2D”, which includes any digital mode with a bandwidth of 2.8 kHz or less whose technical characteristics have been documented publicly, per Part 97.309(4) of the FCC Rules. Such modes would include PACTOR I, II, or III, 300 baud packet, MFSK , MT63 , Contestia , Olivia , DominoEX, and others. On 60 meters , hams are restricted to only one signal per channel, and automatic operation
450-462: A combination of other atmospheric factors can occasionally cause skips that duct high-power signals to places well over 1000 km (600 miles) away. Non-broadcast signals are also affected. Mobile phone signals are in the UHF band, ranging from 700 to over 2600 MHz, a range which makes them even more prone to weather-induced propagation changes. In urban (and to some extent suburban ) areas with
540-700: A distance of more than 6 000 km (4 000 miles). Tropo-scatter happens when water droplets and dust particles refract a VHF or UHF signal over the horizon. Using relatively high power and a high gain antenna, this propagation will give marginal enhanced over-the-horizon VHF and UHF communications up to several hundred kilometres (miles). During the 1970s commercial "scatter site" operators using huge parabolic antennas and high power used this mode successfully for telephone communications services into northern remote Alaska and Canadian communities. Satellite, buried fibre optic, and terrestrial microwave access have relegated commercial use of tropo-scatter to
630-586: A few hundred miles. At different frequencies, radio waves travel through the atmosphere by different mechanisms or modes: Ground waves . Ground waves . E, F layer ionospheric refraction at night, when D layer absorption weakens. F1, F2 layer ionospheric refraction. Infrequent E ionospheric (E s ) refraction . Uncommonly F2 layer ionospheric refraction during high sunspot activity up to 50 MHz and rarely to 80 MHz. Sometimes tropospheric ducting or meteor scatter In free space , all electromagnetic waves (radio, light, X-rays, etc.) obey
720-926: A formal ITU Region-1 allocation at WRC-19 of 50-52 MHz, with some non-European countries allocating up to 50-54MHz. For example, the United Kingdom , has an allocation in the 6 meter band between 50 and 52 MHz, split as 50–51 MHz amateur primary, and the rest is secondary, with a lower power limit. A detailed bandplan can be obtained from the Radio Society of Great Britain (RSGB) website. this has 50.0-50.5 MHz for narrowband DX modes and propagation beacons, whilst wider bandwidth FM, repeaters and Digital modes can be used in 50.5-52 MHz, including experimental Digital-ATV. Many organizations promote regular competitions in this frequency range to promote its use and to familiarize operators to its quirks. For example, RSGB VHF Contest Committee has
810-417: A free-space path by one-half. Radio waves in vacuum travel at the speed of light . The Earth's atmosphere is thin enough that radio waves in the atmosphere travel very close to the speed of light, but variations in density and temperature can cause some slight refraction (bending) of waves over distances. Line-of-sight refers to radio waves which travel directly in a line from the transmitting antenna to
900-654: A future allocation of 50–54 MHz to amateur radio in Region ;1. 6 meter frequency allocations for amateur radio are not universal worldwide. In the United States and Canada, the band ranges from 50-54 MHz. In some other countries, the band is restricted to military communications . Further, in a few nations, the frequency range is still used for television transmissions, although most countries have (re)assigned those television channels to higher frequencies (see TV channel 1 ). For many years
990-468: A gap that would become the Amateur radio 6-meter band in the United States. FCC Order 130-C went into effect at 3 am Eastern Standard Time on March 1, 1946, and created the 6-meter band allocation for the amateur service as 50–54 MHz. Emission types A1, A2, A3 and A4 were allowed for the entire band and special emission for frequency modulation telephony was allowed from 52.5 to 54 MHz. At
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#17327726512001080-432: A high population density , this is partly offset by the use of smaller cells, which use lower effective radiated power and beam tilt to reduce interference, and therefore increase frequency reuse and user capacity. However, since this would not be very cost-effective in more rural areas, these cells are larger and so more likely to cause interference over longer distances when propagation conditions allow. While this
1170-500: A large number of contests on 6 meters every year. Because of its peculiarity, there are a number of 6 meter band operator groups. These people monitor the status of the band between different paths and promote 6 meter band operations. For a full list of countries using 6 meters, refer to the bandplan of the International Amateur Radio Union . Because the 6 meter band is just below
1260-658: A period of time following World War II, but lost the band to UK analogue television channel 4 . They gained a 4-meter band in 1956 and eventually gained the 6 meter band from 50–52 MHz, when it was decided to terminate analogue television broadcasts on channel 2. The Radio Regulations of the International Telecommunication Union allow amateur radio operations in the frequency range from 50.000–54.000 MHz in ITU Regions ;2 and 3. At ITU level, Region 1
1350-458: A physical object present in the innermost Fresnel zone . Obstacles that commonly cause NLOS propagation include buildings, trees, hills, mountains, and, in some cases, high voltage electric power lines. Some of these obstructions reflect certain radio frequencies, while some simply absorb or garble the signals; but, in either case, they limit the use of many types of radio transmissions, especially when low on power budget. Lower power levels at
1440-422: A point source. Doubling the distance of a receiver from a transmitter means that the power density of the radiated wave at that new location is reduced to one-quarter of its previous value. The power density per surface unit is proportional to the product of the electric and magnetic field strengths. Thus, doubling the propagation path distance from the transmitter reduces each of these received field strengths over
1530-645: A receiver reduce the chance of successfully receiving a transmission. Low levels can be caused by at least three basic reasons: low transmit level, for example Wi-Fi power levels; far-away transmitter, such as 3G more than 5 miles (8.0 km) away or TV more than 31 miles (50 km) away; and obstruction between the transmitter and the receiver, leaving no clear path. NLOS lowers the effective received power. Near Line Of Sight can usually be dealt with using better antennas, but Non Line Of Sight usually requires alternative paths or multipath propagation methods. How to achieve effective NLOS networking has become one of
1620-641: A search of the ACMA Radcomms register [2] . ) The Wireless Institute of Australia has charts for Amateur frequencies for Australia . The New Zealand Association of Radio Transmitters (NZART) has charts for Amateur frequencies for New Zealand . The Japanese have charts for Amateur frequencies in Japan Radio amateurs may engage in satellite and space craft communications; however, the frequencies allowed for such activities are allocated separately from more general use radio amateur bands. Under
1710-424: A significant depth into seawater, and so are used for one-way military communication to submerged submarines. Early long-distance radio communication ( wireless telegraphy ) before the mid-1920s used low frequencies in the longwave bands and relied exclusively on ground-wave propagation. Frequencies above 3 MHz were regarded as useless and were given to hobbyists ( radio amateurs ). The discovery around 1920 of
1800-477: A simple antenna, range would be around 50 km (30 miles). With a large antenna system like a long yagi , and higher power (typically 100 watts or more) contacts of around 1 000 km (600 miles) using the Morse code (CW) and single-sideband (SSB) modes are common. Ham operators seek to exploit the limits of the frequencies usual characteristics looking to learn, understand, and experiment with
1890-599: A slight "drag" on the bottom of the radio waves, bending the signals down such that they can follow the Earth's curvature over the normal radio horizon. The result is typically several stations being heard from another media market – usually a neighboring one, but sometimes ones from a few hundred kilometers (miles) away. Ice storms are also the result of inversions, but these normally cause more scattered omnidirection propagation, resulting mainly in interference, often among weather radio stations. In late spring and early summer,
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#17327726512001980-408: A straight line from the transmitting antenna to the receiving antenna. Line of sight transmission is used for medium-distance radio transmission, such as cell phones , cordless phones , walkie-talkies , wireless networks , FM radio , television broadcasting , radar , and satellite communication (such as satellite television ). Line-of-sight transmission on the surface of the Earth is limited to
2070-470: A transmitter or modeling the distribution of signals over different regions. Because each individual telecommunication link has to encounter different terrain, path, obstructions, atmospheric conditions and other phenomena, it is intractable to formulate the exact loss for all telecommunication systems in a single mathematical equation. As a result, different models exist for different types of radio links under different conditions. The models rely on computing
2160-483: Is allocated to broadcasting. However, in practice a large number of ITU Region 1 countries allow amateur use of at least some of the 6 meter band. Over the years portions have been vacated by VHF television broadcasting channels for one reason or another. In November 2015 the ITU World Radio Conference (WRC-15) agreed that for their next conference in 2019, Agenda Item 1.1 would study
2250-622: Is available for use in several countries, and the 2007 World Radiocommunication Conference (WRC-07) recommended it as a worldwide amateur allocation. Before the introduction of the 2 200 metre band in the U.K. in 1998, operation on the even lower frequency of 73 kHz, in the LF time signal band, was allowed from 1996–2003. ITU Region 1 corresponds to Europe, Russia, Africa and the Middle East. For ITU region 1, Radio Society of Great Britain 's band plan will be more definitive (click on
2340-412: Is customarily used for local FM communications, repeaters, radio control. In North America, especially in the United States and Canada, the 6-meter band may be used by licensed amateurs for the safe operation of radio-controlled (RC) aircraft and other types of radio control hobby miniatures. By general agreement among the amateur radio community, 200 kHz of the 6 meter band is reserved for
2430-661: Is done by national telecommunication authorities. Globally, the International Telecommunication Union (ITU) oversees how much radio spectrum is set aside for amateur radio transmissions. Individual amateur stations are free to use any frequency within authorized frequency ranges; authorized bands may vary by the class of the station license. Radio amateurs use a variety of transmission modes, including Morse code , radioteletype , data, and voice. Specific frequency allocations vary from country to country and between ITU regions as specified in
2520-431: Is generally transparent to the user thanks to the way that cellular networks handle cell-to-cell handoffs , when cross-border signals are involved, unexpected charges for international roaming may occur despite not having left the country at all. This often occurs between southern San Diego and northern Tijuana at the western end of the U.S./Mexico border , and between eastern Detroit and western Windsor along
2610-491: Is most common from November through early February. The 6-meter band shares many characteristics with the neighboring 8-meter band , but it is somewhat higher in frequency. On October 10, 1924, the 5-meter band (56–64 MHz) was first made available to amateurs in the United States by the Third National Radio Conference. On October 4, 1927, the band was allocated on a worldwide basis by
2700-588: Is not permitted. In addition, the FCC continues to require that all digital transmissions be centred on the channel-centre frequencies, which the Report and Order defines as being 1.5 kHz above the suppressed carrier frequency of a transceiver operated in the upper side-band (USB) mode. As amateur radio equipment displays the carrier frequency, it is important for operators to understand correct frequency calculations for digital "sound-card" modes to ensure compliance with
2790-517: Is not really a propagation mode, but rather an active repeater system. Satellites have been highly successful in providing VHF/UHF/SHF users "propagation" beyond the horizon. Amateurs have sponsored the launch of dozens of communications satellites since the 1970s. These satellites are usually known as OSCARs (Orbiting Satellite Carrying Amateur Radio). Also, the ISS has amateur radio repeaters and radio location services on board. Amateur television (ATV)
6-meter band - Misplaced Pages Continue
2880-455: Is on the order of 270 dB for 70 cm signals. Return signals are weak and distorted because of the relative velocities of the transmitting station, Moon and the receiving station. The Moon's surface is also very rocky and irregular. Because of the weak, distorted return signals, Moon bounce communications use digital modes. For example, old-fashioned Morse code or modern JT65 , designed for working with weak signals. Satellite relay
2970-643: Is proportional to frequency, so ground waves are the main mode of propagation at lower frequencies, in the MF , LF and VLF bands. Ground waves are used by radio broadcasting stations in the MF and LF bands, and for time signals and radio navigation systems. At even lower frequencies, in the VLF to ELF bands, an Earth-ionosphere waveguide mechanism allows even longer range transmission. These frequencies are used for secure military communications . They can also penetrate to
3060-510: Is the hobby of transmitting broadcast -compatible video and audio by amateur radio. It also includes the study and building of such transmitters and receivers and the propagation between these two. In NTSC countries, ATV operation requires the ability to use a 6 MHz wide channel. All bands at VHF or lower are less than 6 MHz wide, so ATV operation is confined to UHF and up. Bandwidth requirements will vary from this for PAL and SECAM transmissions. ATV operation in
3150-584: Is the method used by cell phones , cordless phones , walkie-talkies , wireless networks , point-to-point microwave radio relay links, FM and television broadcasting and radar . Satellite communication uses longer line-of-sight paths; for example home satellite dishes receive signals from communication satellites 22,000 miles (35,000 km) above the Earth, and ground stations can communicate with spacecraft billions of miles from Earth. Ground plane reflection effects are an important factor in VHF line-of-sight propagation. The interference between
3240-511: The International Telecommunication Union did not allocate 6 meter frequencies to amateurs in Europe. However the decline of VHF television broadcasts and commercial pressure on the lower VHF spectrum enabled most European countries to provide a 6 meter amateur allocation. Eventually in 2015, following a proposal by IARU to CEPT, the ITU adopted Agenda Item AI-1.1, which four years later led to
3330-672: The International Telecommunication Union 's rules, all amateur radio operations may only occur within 50 kilometres (31 mi) of the Earth's surface. As such, the Amateur Radio Service is not permitted to engage in satellite operations; however, a sister radio service, called the Amateur Satellite Service , exists which allows satellite operations for the same purposes as the Amateur Radio Service . In most countries, an amateur radio license conveys operating privileges in both services, and in practice,
3420-707: The U.S./Canada border . Since signals can travel unobstructed over a body of water far larger than the Detroit River , and cool water temperatures also cause inversions in surface air, this "fringe roaming" sometimes occurs across the Great Lakes , and between islands in the Caribbean . Signals can skip from the Dominican Republic to a mountainside in Puerto Rico and vice versa, or between
3510-476: The WSPR mode provides maps with real time propagation conditions between a network of transmitters and receivers. Even without special beacons the realtime propagation conditions can be measured: A worldwide network of receivers decodes morse code signals on amateur radio frequencies in realtime and provides sophisticated search functions and propagation maps for every station received. The average person can notice
3600-417: The channelled 60 meter band is the U.S. National Telecommunications and Information Administration (NTIA). Effective 5 March 2012 the FCC permits CW, USB, and certain digital modes on these frequencies by amateurs on a secondary basis. The FCC Report and Order permits the use of digital modes that comply with emission designator “60H0J2B”, which includes PSK31 as well as any RTTY signal with
3690-549: The frequencies formerly allocated to the old VHF television Channel 2 in North America (54–60 MHz), television interference (TVI) to neighbors' sets was a common problem for amateurs operating in this band prior to June 2009, when analog television transmissions ended in the U.S. Beginning around the turn of the millennium, the availability of transceivers that include the 6 meter band has increased greatly. Many commercial HF transceivers now include
6-meter band - Misplaced Pages Continue
3780-401: The inverse-square law which states that the power density ρ {\displaystyle \rho \,} of an electromagnetic wave is proportional to the inverse of the square of the distance r {\displaystyle r\,} from a point source or: At typical communication distances from a transmitter, the transmitting antenna usually can be approximated by
3870-752: The ionosphere , a layer of charged particles ( ions ) high in the atmosphere. This means that medium and short radio waves transmitted at an angle into the sky can be refracted back to Earth at great distances beyond the horizon – even transcontinental distances. This is called skywave propagation . It is used by amateur radio operators to communicate with operators in distant countries, and by shortwave broadcast stations to transmit internationally. In addition, there are several less common radio propagation mechanisms, such as tropospheric scattering (troposcatter), tropospheric ducting (ducting) at VHF frequencies and near vertical incidence skywave (NVIS) which are used when HF communications are desired within
3960-457: The kilohertz -wide allocations in the HF bands. forwarding systems While "line of sight" propagation is a primary factor for range calculation, much of the interest in the bands above HF comes from use of other propagation modes. A signal transmitted on VHF from a hand-held portable will typically travel about 5–10 km (3–6 miles) depending on terrain. With a low power home station and
4050-588: The medium-wave broadcast band , but in recent times, as the historic users of these low frequencies have been vacating the spectrum, limited space has opened up to allow for new amateur radio allocations and special experimental operations. Since parts of the 500 kHz band are no longer used for regular maritime communications, some countries permit amateur radio radiotelegraph operations in that band. Many countries, however, continue to restrict these frequencies which were historically reserved for maritime and aviation distress calls. The 2 200 metre band
4140-422: The telecommand of models, by licensed amateurs using amateur frequencies. The sub-band reserved for this use is 50.79–50.99 MHz with ten "specified" frequencies, numbered "00" through "09", spaced at 20 kHz apart from 50.800–50.980 MHz. The upper end of the band, starting at 53.0 MHz, and going upwards in 100 kHz steps to 53.8 MHz, used to be similarly reserved for RC modelers, but with
4230-430: The " magic band ". In the northern hemisphere, activity peaks from May through early August, when regular sporadic E propagation enables long-distance contacts spanning up to 2,500 kilometres (1,600 mi) for single-hop propagation. Multiple-hop sporadic E propagation allows intercontinental communications at distances of up to 10,000 kilometres (6,200 mi). In the southern hemisphere, sporadic E propagation
4320-596: The 11 year sunspot cycle. The longest terrestrial contact ever reported on 2 metres (146 MHz) was between a station in Italy and a station in South Africa, a distance of 7 784 km (4 837 miles), using trans-equatorial anomalous enhancement (TE) of the ionosphere over the geomagnetic equator. This enhancement is known as TE, or trans-equatorial propagation and (usually) occurs at latitudes 2 500–3 000 km (1500–1900 miles) within either side of
4410-600: The 1947 International Radio Conference in Atlantic City, New Jersey , the amateur service was allocated 50–54 MHz in ITU Region 2 and 3. Broadcasting was allocated from 41 to 68 MHz in ITU Region 1, but allowed exclusive amateur use of the 6-meter band (50–54 MHz) in a portion of southern Africa. Amateurs in the United Kingdom remained in the 5-meter band (58.5–60 MHz) for
4500-412: The 6 meter band along with shortwave , as do a few handheld VHF/ UHF transceivers. There are also a number of stand-alone 6 meter band transceivers, although commercial production of these has been relatively rare in recent years. Despite support in more available radios, however, the 6 meter band does not share the popularity of amateur radio's 2-meter band . This is due, in large part, to
4590-546: The 6 meter band. Many of these operators develop a real affection for the challenge of the band, and often continue to devote much time to it, even when they gain access to the HF frequencies after upgrading their licenses. For antennas, horizontal polarization is used for 6 meter weak signal, SSB communications using tropospheric propagation , sporadic-E, and multi-hop sporadic-E, and for other propagation modes where polarization does not matter as much. Vertical polarization
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#17327726512004680-498: The 70 cm band is particularly popular, because the signals can be received on any cable-ready television. Operation in the 33 cm and 23 cm bands is easily augmented by the availability of various varieties of consumer-grade wireless video devices that exist and operate in unlicensed frequencies coincident to these bands. Repeater ATV operation requires specially-equipped repeaters. Historically, amateur stations have rarely been allowed to operate on frequencies lower than
4770-463: The European region. The conference maintained the 56–60 MHz allocation for other regions and allowed administrations in Europe latitude to allow amateurs to continue using 56–58.5 MHz. Starting in 1938, the FCC created 6 MHz wide television channel allocations working around the 5-meter amateur band with channel 2 occupying 50–56 MHz. In 1940, television channel 2
4860-516: The ITU's Table of Frequency Allocations . These allocations may only apply to a group of countries. Radio propagation Radio propagation is the behavior of radio waves as they travel, or are propagated , from one point to another in vacuum , or into various parts of the atmosphere . As a form of electromagnetic radiation , like light waves, radio waves are affected by the phenomena of reflection , refraction , diffraction , absorption , polarization , and scattering . Understanding
4950-875: The International Radiotelegraph Conference in Washington, D.C. 56–60 MHz was allocated for amateur and experimental use. There was no change to this allocation at the 1932 International Radiotelegraph Conference in Madrid . At the 1938 International Radiocommunication Conference in Cairo , television broadcasting was given priority in a portion of the 5- and 6-meter band in Europe. Television and low power stations, meaning those with less than 1 kW power, were allocated 56–58.5 MHz and amateurs, experimenters and low power stations were allocated 58.5–60 MHz in
5040-485: The U.S. and British Virgin Islands , among others. While unintended cross-border roaming is often automatically removed by mobile phone company billing systems, inter-island roaming is typically not. A radio propagation model , also known as the radio wave propagation model or the radio frequency propagation model , is an empirical mathematical formulation for the characterization of radio wave propagation as
5130-758: The United States. It allows an unidentified maximum radiated RF power output of one watt for RC model operations of any type. IF higher power is used, then all applicable sections of Part 97 must be followed. In Canada, Industry Canada 's RBR-4, Standards for the Operation of Radio Stations in the Amateur Radio Service, limits radio control of craft, for those models intended for use on any amateur radio-allocated frequency, to amateur service frequencies above 30 MHz. [ v ] All allocations are subject to variation by country. For simplicity, only common allocations found internationally are listed. See
5220-456: The amateur satellite community for proposed satellite operating frequencies before deciding local bandplans above 1300 MHz. Not all Member Unions follow this plan. As an example, the ACMA does not allow Australian Amateurs to use 3.700 MHz to 3.768 MHz and 3.800 MHz to 3.900 MHz, allocating this region to Emergency and Ambulatory services (Allocations can be found conducting
5310-502: The band, above 50.1 MHz, by any licensed amateur operator in the United States; however, an indiscriminate choice of frequencies for RC operations is discouraged by the amateur radio community via its self-imposed band plan for 6 meters. In the United States, the Federal Communications Commission 's (FCC) Part 97.215 rules regulate certain telecommand of model craft in the amateur service within
5400-464: The boundaries of these warm/cold atmospheric layers. Radio signals have been known to travel hundreds, even thousands of kilometres (miles) due to these unique weather conditions. For example: The longest distance reported contact due to tropospheric refraction on 2 metres is 4 754 km (2 954 miles) between Hawaii and a ship south of Mexico . There were reports of the reception of one way signals from Réunion to Western Australia ,
5490-594: The buttons at the bottom of the page). The following charts show the voluntary bandplans used by amateurs in ITU Region ;1. Unlike the US, slots for the various transmission modes are not set by the amateur's license but most users do follow these guidelines. ITU Region 2 consists of the Americas, including Greenland. The frequency allocations for hams in ITU Region 2 are: The primary (first priority) user of
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#17327726512005580-637: The channel-center requirement. The ARRL has a "detailed band plan" for US hams showing allocations within each band. RAC has a "chart showing the frequencies available to amateurs in Canada" . 21 June 2017 . Canadian operators are restricted to 100 watts PEP. ITU region 3 consists of Australia, Indonesia, Japan, New Zealand, the South Pacific, and Asia south of Siberia. The IARU frequency allocations for hams in ITU Region 3 are: Bands above 1300 MHz: societies should consult with
5670-413: The conductive surface of the Earth. The wave "clings" to the surface and thus follows the curvature of the Earth, so ground waves can travel over mountains and beyond the horizon. Ground waves propagate in vertical polarization so vertical antennas ( monopoles ) are required. Since the ground is not a perfect electrical conductor, ground waves are attenuated as they follow the Earth's surface. Attenuation
5760-963: The current ITU HF frequency allocations for amateur radio. The list of frequency ranges is called a band allocation , which may be set by international agreements, and national regulations. The modes and types of allocations within each frequency band is called a bandplan ; it may be determined by regulation, but most typically is set by agreements between amateur radio operators. National authorities regulate amateur usage of radio bands. Some bands may not be available or may have restrictions on usage in certain countries or regions. International agreements assign amateur radio bands which differ by region. Frequencies above 30 MHz are referred to as Very High Frequency (VHF) region and those above 300 MHz are called Ultra High Frequency (UHF). The allocated bands for amateurs are many megahertz wide, allowing for high-fidelity audio transmission modes ( FM ) and very fast data transmission modes that are unfeasible for
5850-432: The direct beam line-of-sight and the ground reflected beam often leads to an effective inverse-fourth-power ( 1 ⁄ distance ) law for ground-plane limited radiation. Lower frequency (between 30 and 3,000 kHz) vertically polarized radio waves can travel as surface waves following the contour of the Earth; this is called ground wave propagation. In this mode the radio wave propagates by interacting with
5940-545: The distance to the visual horizon, which depends on the height of transmitting and receiving antennas. It is the only propagation method possible at microwave frequencies and above. At lower frequencies in the MF , LF , and VLF bands, diffraction allows radio waves to bend over hills and other obstacles, and travel beyond the horizon, following the contour of the Earth. These are called surface waves or ground wave propagation . AM broadcast and amateur radio stations use ground waves to cover their listening areas. As
6030-669: The effects of changes in radio propagation in several ways. In AM broadcasting , the dramatic ionospheric changes that occur overnight in the mediumwave band drive a unique broadcast license scheme in the United States, with entirely different transmitter power output levels and directional antenna patterns to cope with skywave propagation at night. Very few stations are allowed to run without modifications during dark hours, typically only those on clear channels in North America . Many stations have no authorization to run at all outside of daylight hours. For FM broadcasting (and
6120-452: The effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for amateur radio communications, international shortwave broadcasters , to designing reliable mobile telephone systems, to radio navigation , to operation of radar systems. Several different types of propagation are used in practical radio transmission systems. Line-of-sight propagation means radio waves which travel in
6210-414: The equator. An intense solar storm causing aurora borealis (northern lights) will also provide occasional propagation enhancement to HF-low (6-metre) band radio waves. Aurorae only occasionally affect signals on the 2 metre band . Signals are often distorted and on the lower frequencies give a curious "watery sound" to normally propagated HF signals. Peak signals usually come from the north, even if
6300-794: The exact behavior of a link, rather, they predict the most likely behavior the link may exhibit under the specified conditions. Different models have been developed to meet the needs of realizing the propagation behavior in different conditions. Types of models for radio propagation include: ELF 3 Hz/100 Mm 30 Hz/10 Mm SLF 30 Hz/10 Mm 300 Hz/1 Mm ULF 300 Hz/1 Mm 3 kHz/100 km VLF 3 kHz/100 km 30 kHz/10 km LF 30 kHz/10 km 300 kHz/1 km MF 300 kHz/1 km 3 MHz/100 m HF 3 MHz/100 m 30 MHz/10 m VHF 30 MHz/10 m 300 MHz/1 m Amateur radio frequency allocations Amateur radio frequency allocation
6390-437: The few remaining low-band TV stations ), weather is the primary cause for changes in VHF propagation, along with some diurnal changes when the sky is mostly without cloud cover . These changes are most obvious during temperature inversions, such as in the late-night and early-morning hours when it is clear, allowing the ground and the air near it to cool more rapidly. This not only causes dew , frost , or fog , but also causes
6480-406: The first crude empirical rule of radio propagation: the maximum transmission distance varied as the square of the height of the antenna. As the path loss encountered along any radio link serves as the dominant factor for characterization of propagation for the link, radio propagation models typically focus on realization of the path loss with the auxiliary task of predicting the area of coverage for
6570-471: The frequency gets lower, the attenuation with distance decreases, so very low frequency (VLF) to extremely low frequency (ELF) ground waves can be used to communicate worldwide. VLF to ELF waves can penetrate significant distances through water and earth, and these frequencies are used for mine communication and military communication with submerged submarines . At medium wave and shortwave frequencies ( MF and HF bands), radio waves can refract from
6660-403: The history books. Because of high cost and complexity this mode is usually out of reach for the average amateur radio operator. F2 and TE band openings from other ionospheric reflection/refraction modes, or sky-wave propagation as it is known can also occasionally occur on the low band VHF frequencies of 6 or 4 metres, and very rarely on 2 metres (high band VHF) during extreme peaks in
6750-444: The ionospheric reflection or skywave mechanism made the medium wave and short wave frequencies useful for long-distance communication and they were allocated to commercial and military users. Non-line-of-sight (NLOS) radio propagation occurs outside of the typical line-of-sight (LOS) between the transmitter and receiver, such as in ground reflections . Near-line-of-sight (also NLOS) conditions refer to partial obstruction by
6840-587: The larger size of 6 meter antennas, power limitations in some countries outside the United States, and the 6 meter band's greater susceptibility to local electrical interference. As transceivers have become more available for the 6 meter band, it has quickly gained popularity. In many countries, including the United States , access is granted to entry-level license holders. Those without access to international HF frequencies often gain their first experience with truly long-distance communications on
6930-432: The legal distinction between the two services is transparent to the average licensee. The primary reason the two services are separate is to limit the frequencies available for satellite operations. Due to the shared nature of the amateur radio allocations internationally, and the nature of satellites to roam worldwide, the ITU does not consider all amateur radio bands appropriate for satellite operations. Being separate from
7020-493: The link could actually become NLOS but the quality of the radio channel could be virtually unaffected. If, instead, a large building was constructed in the path making it NLOS, the channel may be impossible to receive. HF propagation conditions can be simulated using radio propagation models , such as the Voice of America Coverage Analysis Program , and realtime measurements can be done using chirp transmitters . For radio amateurs
7110-452: The major questions of modern computer networking. Currently, the most common method for dealing with NLOS conditions on wireless computer networks is simply to circumvent the NLOS condition and place relays at additional locations, sending the content of the radio transmission around the obstructions. Some more advanced NLOS transmission schemes now use multipath signal propagation, bouncing
7200-511: The median path loss for a link under a certain probability that the considered conditions will occur. Radio propagation models are empirical in nature, which means, they are developed based on large collections of data collected for the specific scenario. For any model, the collection of data has to be sufficiently large to provide enough likeliness (or enough scope) to all kind of situations that can happen in that specific scenario. Like all empirical models, radio propagation models do not point out
7290-784: The possibilities of these enhanced propagation modes. Occasionally, several different ionospheric conditions allow signals to travel beyond the ordinary line-of-sight limits. Some amateurs on VHF seek to take advantage of "band openings" where natural occurrences in the atmosphere and ionosphere extend radio transmission distances well over their normal range. Many hams listen for hours hoping to take advantage of these occasional extended propagation "openings". The ionospheric conditions are called sporadic E and anomalous enhancement . Less frequently used anomalous modes are tropospheric scatter and Aurora Borealis (Northern Lights). Moon bounce and satellite relay are also possible. Some openings are caused by islands of intense ionization of
7380-429: The radio wave propagation and therefore the quality of operation of a radio channel, if it is possible at all, over an NLOS path. The acronym NLOS has become more popular in the context of wireless local area networks (WLANs) and wireless metropolitan area networks such as WiMAX because the capability of such links to provide a reasonable level of NLOS coverage greatly improves their marketability and versatility in
7470-403: The radio signal off other nearby objects to get to the receiver. Non-Line-of-Sight (NLOS) is a term often used in radio communications to describe a radio channel or link where there is no visual line of sight (LOS) between the transmitting antenna and the receiving antenna . In this context LOS is taken There are many electrical characteristics of the transmission media that affect
7560-453: The receiving antenna, often also called direct-wave. It does not necessarily require a cleared sight path; at lower frequencies radio waves can pass through buildings, foliage and other obstructions. This is the most common propagation mode at VHF and above, and the only possible mode at microwave frequencies and above. On the surface of the Earth, line of sight propagation is limited by the visual horizon to about 40 miles (64 km). This
7650-489: The rise of amateur repeater stations operating above 53 MHz in the United States, and very few 53 MHz RC units in Canada, the move to the lower end of the 6 meter spectrum for radio-controlled model flying activities by amateur radio operators was undertaken in North America, starting in the early 1980s, and more-or-less completed by 1991. It is still completely legal for ground-level RC model operation (cars, boats, etc.) to be accomplished on any frequency within
7740-477: The signal originates from a station to the east or west of the receiver. This effect is most significant in the latitudes north of 45 degrees. Amateurs do successfully communicate by bouncing their signals off the surface of the Moon, called Earth-Moon-Earth (EME) transmission. The mode requires moderately high power (more than 500 watts) and a fairly large, high-gain antenna because round-trip path loss
7830-459: The spring and early summer months. This phenomenon occurs during the fall months, although not as often. Band openings are sometimes caused by a weather phenomenon known as a tropospheric "inversion" , where a stagnant high pressure area causes alternating stratified layers of warm and cold air generally trapping the colder air beneath. This may make for smoggy or foggy days, but it also causes VHF and UHF radio transmissions to travel or duct along
7920-401: The typical urban environments where they are most frequently used. However NLOS contains many other subsets of radio communications. The influence of a visual obstruction on a NLOS link may be anything from negligible to complete suppression. An example might apply to a LOS path between a television broadcast antenna and a roof mounted receiving antenna. If a cloud passed between the antennas
8010-525: The upper atmosphere, known as the E ;Layer ionosphere . These islands of intense ionization are called " sporadic E " and result in erratic but often strong propagation characteristics on the "low[er] band" VHF radio frequencies. The 6 metre amateur band falls into this category, often called "the magic band", will often "open up" from one small area into another small geographic area 1 000–1 700 km (600–1 000 miles) away during
8100-501: Was reallocated to 60 MHz and TV channel 1 was moved to 50–56 MHz maintaining a gap for the 5-meter amateur band. When the US entered World War II, transmissions by amateur radio stations were suspended for the duration of the war. After the war, the 5-meter band was briefly reopened to amateurs from 56–60 MHz until March 1, 1946. At that time the FCC moved television channel 2 down to 54–60 MHz and reallocated channel 1 down to 44–50 MHz opening
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