Low frequency or LF is the ITU designation for radio frequencies in the range of 30 kilohertz to 300 kHz. As its wavelengths range from ten kilometres to one kilometre it is 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 and weather systems. A number of time signal broadcasts are broadcast in this band; because of their long wavelength, low frequency radio waves can diffract over obstacles like mountain ranges and travel beyond the horizon, following the contour of the Earth. This mode of propagation, called ground wave, is the main mode in the LF band. Ground waves must be vertically polarized, so vertical monopole antennas are used for transmitting; the attenuation of signal strength with distance by absorption in the ground is lower than at higher frequencies.
Low frequency ground waves can be received up to 2,000 kilometres from the transmitting antenna. Low frequency waves can occasionally travel long distances by reflecting from the ionosphere, although this method, called skywave or "skip" propagation, is not as common as at higher frequencies. Reflection occurs at F layers. Skywave signals can be detected at distances exceeding 300 kilometres from the transmitting antenna. In Europe and Japan, many low-cost consumer devices have since the late 1980s contained radio clocks with an LF receiver for these signals. Since these frequencies propagate by ground wave only, the precision of time signals is not affected by varying propagation paths between the transmitter, the ionosphere, the receiver. In the United States, such devices became feasible for the mass market only after the output power of WWVB was increased in 1997 and 1999. Radio signals below 50 kHz are capable of penetrating ocean depths to 200 metres, the longer the wavelength, the deeper.
The British, Indian, Swedish, United States and other navies communicate with submarines on these frequencies. In addition, Royal Navy nuclear submarines carrying ballistic missiles are under standing orders to monitor the BBC Radio 4 transmission on 198 kHz in waters near the UK, it is rumoured that they are to construe a sudden halt in transmission of the morning news programme Today, as an indicator that the UK is under attack, whereafter their sealed orders take effect. In the US, the Ground Wave Emergency Network or GWEN operated between 150 and 175 kHz, until replaced by satellite communications systems in 1999. GWEN was a land based military radio communications system which could survive and continue to operate in the case of a nuclear attack; the 2007 World Radiocommunication Conference made this band a worldwide amateur radio allocation. An international 2.1 kHz allocation, the 2200 meter band, is available to amateur radio operators in several countries in Europe, New Zealand and French overseas dependencies.
The world record distance for a two-way contact is over 10,000 km from near Vladivostok to New Zealand. As well as conventional Morse code many operators use slow computer-controlled Morse code or specialized digital communications modes; the UK allocated a 2.8 kHz sliver of spectrum from 71.6 kHz to 74.4 kHz beginning in April 1996 to UK amateurs who applied for a Notice of Variation to use the band on a noninterference basis with a maximum output power of 1 Watt ERP. This was withdrawn on 30 June 2003 after a number of extensions in favor of the European-harmonized 136 kHz band. Slow Morse Code from G3AQC in the UK was received 3,275 miles away, across the Atlantic Ocean, by W1TAG in the US on 21-22 November 2001 on 72.401 kHz. In the United States, there is a exemption within FCC Part 15 regulations permitting unlicensed transmissions in the frequency range of 160 to 190 kHz. Longwave radio hobbyists refer to this as the' LowFER' band, experimenters, their transmitters are called'LowFERs'.
This frequency range between 160 kHz and 190 kHz is referred to as the 1750 Meter band. Requirements from 47CFR15.217 and 47CFR15.206 include: The total input power to the final radio frequency stage shall not exceed one watt. The total length of the transmission line and ground lead shall not exceed 15 meters. All emissions below 160 kHz or above 190 kHz shall be attenuated at least 20 dB below the level of the unmodulated carrier; as an alternative to these requirements, a field strength of 2400/F microvolts/meter may be used. In all cases, operation may not cause harmful interference to licensed services. Many experimenters in this band are amateur radio operators. A regular service transmitting RTTY marine meteorological information in SYNOP code on LF is the German Meteorological Service; the DWD operates station DDH47 on 147.3 kHz using standard ITA-2 alphabet with a transmission speed of 50 baud and FSK modulation with 85 Hz shift. In parts of the world where there is no longwave broadcasting service, Non-directional beacons used for aeronavigation operate on 190–300 kHz.
In Europe and Africa, the NDB allocation starts on 283.5 kHz. The LORAN-C radio navigation system operated on 100 kHz. In the past, the Decca Navigator System operated betw
High-voltage direct current
A high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. For underwater power cables, HVDC avoids the heavy currents required to charge and discharge the cable capacitance each cycle. For shorter distances, the higher cost of DC conversion equipment compared to an AC system may still be justified, due to other benefits of direct current links. HVDC uses voltages between 100 kV and 1,500 kV. HVDC allows power transmission between unsynchronized AC transmission systems. Since the power flow through an HVDC link can be controlled independently of the phase angle between source and load, it can stabilize a network against disturbances due to rapid changes in power. HVDC allows transfer of power between grid systems running at different frequencies, such as 50 Hz and 60 Hz.
This improves the stability and economy of each grid, by allowing exchange of power between incompatible networks. The modern form of HVDC transmission uses technology developed extensively in the 1930s in Sweden and in Germany. Early commercial installations included one in the Soviet Union in 1951 between Moscow and Kashira, a 100 kV, 20 MW system between Gotland and mainland Sweden in 1954; the longest HVDC link in the world is the Rio Madeira link in Brazil, which consists of two bipoles of ±600 kV, 3150 MW each, connecting Porto Velho in the state of Rondônia to the São Paulo area. The length of the DC line is 2,375 km. In July 2016, ABB Group received a contract in China to build an ultrahigh-voltage direct-current land link with a 1100 kV voltage, a 3,000 km length and 12 GW of power, setting world records for highest voltage, longest distance, largest transmission capacity. High voltage is used for electric power transmission to reduce the energy lost in the resistance of the wires. For a given quantity of power transmitted, doubling the voltage will deliver the same power at only half the current.
Since the power lost as heat in the wires is directly proportional to the square of the current, doubling the voltage reduces the line losses by a factor of 4. While power lost in transmission can be reduced by increasing the conductor size, larger conductors are heavier and more expensive. High voltage cannot be used for lighting or motors, so transmission-level voltages must be reduced for end-use equipment. Transformers are used to change the voltage levels in alternating current transmission circuits. Transformers made voltage changes practical, AC generators were more efficient than those using DC; because of this, AC became dominant after the conclusion of the War of Currents in 1892. The War of Currents was a competition fought in the US between the DC system of Thomas Edison and the AC system of George Westinghouse. Practical conversion of power between AC and DC became possible with the development of power electronics devices such as mercury-arc valves and, starting in the 1970s, semiconductor devices as thyristors, integrated gate-commutated thyristors, MOS-controlled thyristors and insulated-gate bipolar transistors.
The first long-distance transmission of electric power was demonstrated using direct current in 1882 at Miesbach-Munich Power Transmission, but only 1.5 kW was transmitted. An early method of high-voltage DC transmission was developed by the Swiss engineer René Thury and his method was put into practice by 1889 in Italy by the Acquedotto De Ferrari-Galliera company; this system used series-connected motor-generator sets to increase the voltage. Each set was driven by insulated shafts from a prime mover; the transmission line was operated in a'constant current' mode, with up to 5,000 volts across each machine, some machines having double commutators to reduce the voltage on each commutator. This system transmitted 630 kW at 14 kV DC over a distance of 120 km; the Moutiers–Lyon system transmitted 8,600 kW of hydroelectric power a distance of 200 km, including 10 km of underground cable. This system used eight series-connected generators with dual commutators for a total voltage of 150 kV between the positive and negative poles, operated from c.1906 until 1936.
Fifteen Thury systems were in operation by 1913. Other Thury systems operating at up to 100 kV DC worked into the 1930s, but the rotating machinery required high maintenance and had high energy loss. Various other electromechanical devices were tested during the first half of the 20th century with little commercial success. One technique attempted for conversion of direct current from a high transmission voltage to lower utilization voltage was to charge series-connected batteries reconnect the batteries in parallel to serve distribution loads. While at least two commercial installations were tried around the turn of the 20th century, the technique was not useful owing to the limited capacity of batteries, difficulties in switching between series and parallel connections, the inherent energy inefficiency of a battery charge/discharge cycle. First proposed in 1914, the grid controlled mercury-arc valve became available for power transmission during the period 1920 to 1940. Starting in 1932, General Electric tested mercury-vapor valves and a 12 kV DC transmission line, which served to convert 40 Hz generation to serve 60 Hz loads, at Mechanicville, New York.
In 1941, a 60 MW, ±200 kV, 115 km buried cable
Amateur radio operator
An amateur radio operator is someone who uses equipment at an amateur radio station to engage in two-way personal communications with other amateur operators on radio frequencies assigned to the amateur radio service. Amateur radio operators have been granted an amateur radio license by a governmental regulatory authority after passing an examination on applicable regulations, radio theory, radio operation; as a component of their license, amateur radio operators are assigned a call sign that they use to identify themselves during communication. There are about three million amateur radio operators worldwide. Amateur radio operators are known as radio amateurs or hams; the term "ham" as a nickname for amateur radio operators originated in a pejorative usage by operators in commercial and professional radio communities, dates to wired telegraphy. The word was subsequently adopted by amateur radio operators. Few governments maintain detailed demographic statistics of their amateur radio operator populations, aside from recording the total number of licensed operators.
The majority of amateur radio operators worldwide reside in Japan, the United States, South Korea, the nations of Europe. The top five countries by percentage of the population are Japan, Taiwan, South Korea and Thailand. Only the governments of Yemen and North Korea prohibit their citizens from becoming amateur radio operators. In some countries, acquiring an amateur radio license is difficult because of the bureaucratic processes or fees that place access to a license out of reach for most citizens. Most nations permit foreign nationals to earn an amateur radio license, but few amateur radio operators are licensed in multiple countries. In the vast majority of countries, the population of amateur radio operators is predominantly male. In China, 12% of amateur radio operators are women, while 15% of amateur radio operators in the United States are women; the Young Ladies Radio League is an international organization of female amateur radio operators. A male amateur radio operator can be referred to as an OM, an abbreviation used in Morse code telegraphy for "old man", regardless of the operator's age.
A female amateur radio operator can be referred to as a YL, from the abbreviation used for "young lady", regardless of the operator's age. XYL was once used by amateur radio operators to refer to an unlicensed woman the wife of a male amateur radio operator. Sometimes the wife of a ham operator is called a YF. Although these codes are derived from English language abbreviations, their use is common among amateur radio operators worldwide. In most countries there is no minimum age requirement to earn an amateur radio license and become an amateur radio operator. Although the number of amateur radio operators in many countries increases from year to year, the average age of amateur radio operators is quite high. In some countries, the average age is over 80 years old, with most amateur radio operators earning their license in their 40s or 50s; some national radio societies have responded to this by developing programs to encourage youth participation in amateur radio, such as the American Radio Relay League's Amateur Radio Education and Technology Program.
The World Wide Young Contesters organization promotes youth involvement amongst Europeans, in competitive radio contesting. A strong tie exists between the amateur radio community and the Scouting movement to introduce radio technology to youth. WOSM's annual Jamboree On The Air is Scouting's largest activity, with a half million Scouts and Guides speaking with each other using amateur radio each October. NOTE: AA.. US Armed Forces Americas AE.. US Armed Forces Africa/Canada/Europe/Middle East AP.. US Armed Forces Pacific AS.. American Samoa GU.. Guam MP.. Mariana Islands PR.. Puerto Rico VI.. US Virgin Islands NOTE: ZZ.. Canadian amateurs outside of Canada When referring to a person, the phrase Silent Key and its abbreviation SK indicates an amateur radio operator, deceased; the procedural signal "SK" has been used in Morse code as the last signal sent from a station before ending operation just before shutting off the transmitter. Since this was the last signal received by other operators, the code was adopted to refer to any amateur radio operator, deceased, regardless of whether they were known to have used telegraphy in their communications
High-speed multimedia radio
High-speed multimedia radio is the implementation of wireless data networks over amateur radio frequencies using commercial off-the-shelf hardware such as 802.11 access points. Only licensed amateur radio operators may use amplifiers and specialized antennas to increase the power and coverage of the 802.11 signal. The idea behind this implementation is to use the Amateur bands, namely 420 MHz, 900 MHz, 1270 MHz, 2.3 GHz, 3.4 GHz, 5.8 GHz under the U. S. Federal Communications Commission Part 97 rules instead of the Part 15 rules; this enables licensed amateur operators to use higher output power for wireless devices and allows for longer-range communications. Such communications can be used to assist in emergency communications and disaster relief operations and in everyday amateur radio communications. HSMM can support most of the traffic that the Internet does, including video chat, instant messaging, the Web, file transfer, forums; the only differences being that with HSMM, such services are community instead of commercially implemented and it is wireless.
HSMM can be connected to the Internet and used for web surfing, although because of the FCC regulations on permitted content, this is done only when directly used for ham radio activities. Using high gain directional antennas and amplifiers, reliable long-distance wireless links over many miles are possible and only limited by propagation and the radio horizon; the following is a list of the 802.11 channels that overlap into an amateur radio band under the FCC in the United States. Note that the 5 cm amateur band extends from 5.65 to 5.925 GHz, so that there are many frequencies outside the Part 15 ISM/UNII block used for 802.11a. Many commercial grade 802.11a access points can operate in between the normal channels by using 5 MHz channel spacing instead of the standard 20 MHz channel spacing. 802.11a channels 132, 136 and 140 are only available for unlicensed use in ETSI regions. The following images show the overlapping relationship of the Part 15 unlicensed bands and the Part 97 licensed bands.
The images are not to scale. 2.4 GHz 802.11b/g 5.8 GHz 802.11a Acronyms Used: The 802.11a amateur radio band consists of twelve non-overlapping channels in the 5.650–5.925 GHz band. The 802.11a standard uses OFDM or "Orthogonal Frequency Division Multiplexing" to transmit data and therefore is not classified as spread-spectrum. Because of this 802.11a hardware is not subject to the power rules in FCC Part 97 § 97.311 and the maximum allowable output power is 1500 watts PEP. The 802.11b amateur radio band consists of eight overlapping channels in the 2.390–2.450 GHz band. The 802.11b specification uses Direct Sequence Spread Spectrum to transmit data and is subject to the rules of FCC Part 97 § 97.311. Therefore, the maximum allowable power output in the USA is 10 W PEP; the 802.11g amateur radio band consists of eight overlapping channels in the 2.4 GHz band. The 802.11g standard uses OFDM or "Orthogonal Frequency Division Multiplexing" to transmit data and therefore is not classified as spread-spectrum.
Because of this 802.11g hardware is not subject to the power rules in FCC Part 97 § 97.311 and the maximum allowable output power is 1500 W PEP. The 802.11n amateur radio band consists of eight overlapping channels in the 2.4 GHz band. The 802.11n standard uses OFDM or "Orthogonal Frequency Division Multiplexing" to transmit data and therefore is not classified as spread-spectrum. Because of this 802.11n hardware is not subject to the power rules in FCC Part 97 § 97.311 and the maximum allowable output power is 1500 W PEP. The 5 cm band is shared with the fixed-satellite service in ITU Region 1, the radiolocation service. In ITU Region 2 the primary user is military radiolocation naval radar. Amateur radio operators have secondary privileges to the Federal radiolocation service in the entire band and may not cause interference to these users. Amateur operators are allocated this band are in a co-secondary basis with ISM devices and space research. Amateur, space research, ISM operators each have the "right to operate".
Due to the lack of a high number of Part 15 users, the noise level tends to be lower in many parts of the US but can be quite congested in urban centers and on mountaintops. The 13 cm band is shared with Part 15 users as well as the Federal radiolocation service, ISM devices. Amateur radio operators have secondary privileges to the Federal radiolocation service in the entire band and may not cause interference to these users. Amateur radio operators have primary privileges to ISM devices from 2.390–2.417 GHz and secondary privileges from 2.417–2.450 GHz. Because of the high number of Part 15 users, the noise level in this band tends to be rather high; as with any amateur radio mode, stations must identify at least once every 10 minutes. One acceptable method for doing so is to transmit one’s call sign inside an ICMP echo request. If the access point is set to "master" the user’s call sign may be set as the "SSID" and therefore will be transmitted at regular intervals, it is possible to use a DDNS "push" request to automatically send an amateur call sign in plain text every 10 minutes.
This requires that a computer's hostname be set to the call sign of the amateur operator and that the DHCP servers lease time be set to less than or equal to 10 minutes. With this method implemented the computer will send a DNS "push" request that includes the local computers hostname every time the DHCP lease is renewed; this method is supported by all mode
Frequency is the number of occurrences of a repeating event per unit of time. It is referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency; the period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals, radio waves, light. For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time. In physics and engineering disciplines, such as optics and radio, frequency is denoted by a Latin letter f or by the Greek letter ν or ν; the relation between the frequency and the period T of a repeating event or oscillation is given by f = 1 T.
The SI derived unit of frequency is the hertz, named after the German physicist Heinrich Hertz. One hertz means. If a TV has a refresh rate of 1 hertz the TV's screen will change its picture once a second. A previous name for this unit was cycles per second; the SI unit for period is the second. A traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. 60 rpm equals one hertz. As a matter of convenience and slower waves, such as ocean surface waves, tend to be described by wave period rather than frequency. Short and fast waves, like audio and radio, are described by their frequency instead of period; these used conversions are listed below: Angular frequency denoted by the Greek letter ω, is defined as the rate of change of angular displacement, θ, or the rate of change of the phase of a sinusoidal waveform, or as the rate of change of the argument to the sine function: y = sin = sin = sin d θ d t = ω = 2 π f Angular frequency is measured in radians per second but, for discrete-time signals, can be expressed as radians per sampling interval, a dimensionless quantity.
Angular frequency is larger than regular frequency by a factor of 2π. Spatial frequency is analogous to temporal frequency, but the time axis is replaced by one or more spatial displacement axes. E.g.: y = sin = sin d θ d x = k Wavenumber, k, is the spatial frequency analogue of angular temporal frequency and is measured in radians per meter. In the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has an inverse relationship to the wavelength, λ. In dispersive media, the frequency f of a sinusoidal wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave: f = v λ. In the special case of electromagnetic waves moving through a vacuum v = c, where c is the speed of light in a vacuum, this expression becomes: f = c λ; when waves from a monochrome source travel from one medium to another, their frequency remains the same—only their wavelength and speed change. Measurement of frequency can done in the following ways, Calculating the frequency of a repeating event is accomplished by counting the number of times that event occurs within a specific time period dividing the count by the length of the time period.
For example, if 71 events occur within 15 seconds the frequency is: f = 71 15 s ≈ 4.73 Hz If the number of counts is not large, it is more accurate to measure the time interval for a predetermined number of occurrences, rather than the number of occurrences within a specified time. The latter method introduces a random error into the count of between zero and one count, so on average half a count; this is called gating error and causes an average error in the calculated frequency of Δ f = 1 2 T
The 4-metre band is an amateur radio frequency band in the lower high frequency spectrum. The 4-metre band has a unique character and because few countries have an allocation there little dedicated commercial amateur equipment is available. Therefore, most amateurs active on the band are interested in home construction or modification of private mobile radio equipment; as a result, there is a lot of camaraderie on the band and long ragchews are the norm, as long as there is some local activity. Before World War II, British radio amateurs had been allocated a band at 56 MHz. After the war ended, they were allocated the 5-metre band instead; this only lasted until 1949, as by the 5-metre band had been earmarked for BBC Television broadcasts. Meanwhile, in 1948 72-72.8 MHz was allocated to France. In 1956, after several years of intense lobbying by the Radio Society of Great Britain, the 4-metre band was allocated to British radio amateurs as a replacement for the old 5-metre band allocation. For several years the 4-metre band allocation was only 200 kHz wide—from 70.2 MHz to 70.4 MHz.
It was extended to 70.025 MHz to 70.7 MHz. The band limits were subsequently moved to today's allocation of 70.0 MHz to 70.5 MHz. On the occasion of the international Geophysical Year 1957/1958, the following countries have been allocated frequencies between 70-72.8 MHz. Ireland: 70.575-70.775 MHz, Finland: 70.2-70.3 MHz, Germany: 70.3-70.4 MHz, The Netherlands: 70.3-70.4 MHz, Norway: 70.6-72.0 MHz, Yugoslavia: 72.0-72.8 MHz and Austria: 70 MHz special licences. In March 1993 The European Radiocommunications Office of the CEPT launched Phase II of a Detailed Spectrum Investigation covering the frequency range 29.7 - 960 MHz. The results were presented in March 1995. Regarding the Amateur Radio Service the DSI Management Team recommended that 70 MHz to be considered as an amateur band. In addition to the traditional users, an increasing number of countries in Europe and Africa have allocated the 4-metre band to radio amateurs as a result of the decline in VHF television broadcasts on the 4-metre band.
Movement away from the old Eastern European VHF FM broadcast band and migration of commercial stations to higher frequencies have led to slow but steady growth in the number of countries where 4-metre operation is permitted. Whilst not formally allocated at an ITU or Regional level, in Europe CEPT now recognises the increased access to 70 MHz by radio amateurs with footnote'EU9' which has helped underpin further growth. In July 2015 CEPT updated this footnote to recognise it as a formal secondary allocation: "EU9: CEPT administrations may authorise all or parts of the band 69.9-70.5 MHz to the amateur service on a secondary basis."In practice this ranges from 70 MHz to 70.5 MHz in the United Kingdom, with other countries having a smaller allocation within this window. In most countries the maximum power permitted on the band is lower than in other allocations to minimise the possibility of interference with non-amateur services in neighbouring countries. A table with national and regional allocations is pusblished and updated on the Four Metres Website.
The 4-metre band shares many characteristics with the neighbouring 6-metre band. However, as it is somewhat higher in frequency it does not display the same propagation mechanisms via the F2 ionospheric layer seen at HF which appear in 6 metres, leastwise not at temperate latitudes. However, Sporadic E is common on the band in summer, tropospheric propagation is marginally more successful than on the 6-metre band, propagation via the Aurora Borealis and meteor scatter is effective. While Sporadic E permits Europe wide communication, it can be a mixed blessing as the band is still used for wide bandwidth, high power FM broadcasting on the OIRT FM band in a declining number of Eastern European countries. Although this has lessened in recent years, it can still cause considerable interference to both local and long distance operation. First transequatorial propagation contact on 70 MHz took place on 28 March 2011 between Leonidas Fiskas, SV2DCD, in Greece and Willem Badenhorst, ZS6WAB, in South Africa.
Access to the 4-metre band has always been limited by access to suitable 4-metre transceivers. A limited number of transceivers were purposely built for amateurs on this band while converted Private Mobile Radio equipment is in widespread use e.g. Phillips FM1000 and the Ascom SE550; some low power FM commercial equipment is available for the band although it is of simple specifications as suitable for communication of up to around 50 kilometres or so with simple antennas. In the Sporadic E seasons communication around Europe is possible with such equipment; the only Japanese-made, "mass-market" amateur radio transceivers to cover the Four metre band as standard are the Icom IC-7100 and IC-7300 there was the UK specification Yaesu FT-847 with 4m, discontinued in 2005. As a result, many 4-metre users gain access to the band by using converted "Low band" VHF ex-PMR transceivers but invariably these only have either AM or FM and those users who prefer to have a multi-mode capability but can't afford a second hand Yaesu FT-847 use transverters, either purposely built home builds or sometimes converted 6-metre or 2-metre versions.
In recent years there have been extensive imports of Chinese PMR transceivers such as the Wouxun KG-699E 4m and KG-UVD1P1LV DUAL BAND Handheld Transceiver to Western countries so far in the UK and mainl