Effective radiated power
Effective radiated power, synonymous with equivalent radiated power, is an IEEE standardized definition of directional radio frequency power, such as that emitted by a radio transmitter. It is the total power in watts that would have to be radiated by a half-wave dipole antenna to give the same radiation intensity as the actual source at a distant receiver located in the direction of the antenna's strongest beam. ERP measures the combination of the power emitted by the transmitter and the ability of the antenna to direct that power in a given direction, it is equal to the input power to the antenna multiplied by the gain of the antenna. It is used in electronics and telecommunications in broadcasting to quantify the apparent power of a broadcasting station experienced by listeners in its reception area. An alternate parameter that measures the same thing is effective isotropic radiated power. Effective isotropic radiated power is the total power that would have to be radiated by a hypothetical isotropic antenna to give the same signal strength as the actual source in the direction of the antenna's strongest beam.
The difference between EIRP and ERP is that ERP compares the actual antenna to a half-wave dipole antenna, while EIRP compares it to a theoretical isotropic antenna. Since a half-wave dipole antenna has a gain of 1.64, or 2.15 decibels compared to an isotropic radiator, if ERP and EIRP are expressed in watts their relation is E I R P = 1.64 ⋅ E R P If they are expressed in decibels E I R P = E R P + 2.15 Effective radiated power and effective isotropic radiated power both measure the amount of power a radio transmitter and antenna radiates in a specific direction: in the direction of maximum signal strength of its radiation pattern. This maximum radiated power is dependent on two factors: the total power output and the radiation pattern of the antenna – how much of that power is radiated in the desired direction; the latter factor is quantified by the antenna gain, the ratio of the signal strength radiated by an antenna to that radiated by a standard antenna. For example, a 1,000-watt transmitter feeding an antenna with a gain of 4 will have the same signal strength in the direction of its main lobe, thus the same ERP and EIRP, as a 4,000-watt transmitter feeding an antenna with a gain of 1.
So ERP and EIRP are measures of radiated power that can compare different combinations of transmitters and antennas on an equal basis. The difference between ERP and EIRP is that antenna gain has traditionally been measured in two different units, comparing the antenna to two different standard antennas; the decibel gain relative to an isotropic antenna is given by G = 10 log S max S max,isotropic Dipole gain is the ratio of the power density received from the antenna in the direction of its maximum radiation to the power density S max,dipole received from a lossless half-wave dipole antenna in the direction of its maximum radiation G d = S max S max,dipole The decibel gain relative to a dipole is given by G = 10 log S max S max,dipole In contrast to an isotropic antenna, the dipole has a "donut-shaped" radiation pattern, its radiated power is maximum in directions perpendicular to the antenna, declining to zero on the antenna axis. Since the radiation of the dipole is concentrated in horizontal directions, the gain of a half-wave dipole is greater than that of an isotropic antenna.
The isotropic gain of a half-wave dipole is 1.64, or in decibels 10 log 1.64 = 2.15 dBi, so G i = 1.64 G d In decibels G = G + 2.15 {\displ
Low frequency
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
Canada
Canada is a country in the northern part of North America. Its ten provinces and three territories extend from the Atlantic to the Pacific and northward into the Arctic Ocean, covering 9.98 million square kilometres, making it the world's second-largest country by total area. Canada's southern border with the United States is the world's longest bi-national land border, its capital is Ottawa, its three largest metropolitan areas are Toronto and Vancouver. As a whole, Canada is sparsely populated, the majority of its land area being dominated by forest and tundra, its population is urbanized, with over 80 percent of its inhabitants concentrated in large and medium-sized cities, many near the southern border. Canada's climate varies across its vast area, ranging from arctic weather in the north, to hot summers in the southern regions, with four distinct seasons. Various indigenous peoples have inhabited what is now Canada for thousands of years prior to European colonization. Beginning in the 16th century and French expeditions explored, settled, along the Atlantic coast.
As a consequence of various armed conflicts, France ceded nearly all of its colonies in North America in 1763. In 1867, with the union of three British North American colonies through Confederation, Canada was formed as a federal dominion of four provinces; this began an accretion of provinces and territories and a process of increasing autonomy from the United Kingdom. This widening autonomy was highlighted by the Statute of Westminster of 1931 and culminated in the Canada Act of 1982, which severed the vestiges of legal dependence on the British parliament. Canada is a parliamentary democracy and a constitutional monarchy in the Westminster tradition, with Elizabeth II as its queen and a prime minister who serves as the chair of the federal cabinet and head of government; the country is a realm within the Commonwealth of Nations, a member of the Francophonie and bilingual at the federal level. It ranks among the highest in international measurements of government transparency, civil liberties, quality of life, economic freedom, education.
It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many other countries. Canada's long and complex relationship with the United States has had a significant impact on its economy and culture. A developed country, Canada has the sixteenth-highest nominal per capita income globally as well as the twelfth-highest ranking in the Human Development Index, its advanced economy is the tenth-largest in the world, relying chiefly upon its abundant natural resources and well-developed international trade networks. Canada is part of several major international and intergovernmental institutions or groupings including the United Nations, the North Atlantic Treaty Organization, the G7, the Group of Ten, the G20, the North American Free Trade Agreement and the Asia-Pacific Economic Cooperation forum. While a variety of theories have been postulated for the etymological origins of Canada, the name is now accepted as coming from the St. Lawrence Iroquoian word kanata, meaning "village" or "settlement".
In 1535, indigenous inhabitants of the present-day Quebec City region used the word to direct French explorer Jacques Cartier to the village of Stadacona. Cartier used the word Canada to refer not only to that particular village but to the entire area subject to Donnacona. From the 16th to the early 18th century "Canada" referred to the part of New France that lay along the Saint Lawrence River. In 1791, the area became two British colonies called Upper Canada and Lower Canada collectively named the Canadas. Upon Confederation in 1867, Canada was adopted as the legal name for the new country at the London Conference, the word Dominion was conferred as the country's title. By the 1950s, the term Dominion of Canada was no longer used by the United Kingdom, which considered Canada a "Realm of the Commonwealth"; the government of Louis St. Laurent ended the practice of using'Dominion' in the Statutes of Canada in 1951. In 1982, the passage of the Canada Act, bringing the Constitution of Canada under Canadian control, referred only to Canada, that year the name of the national holiday was changed from Dominion Day to Canada Day.
The term Dominion was used to distinguish the federal government from the provinces, though after the Second World War the term federal had replaced dominion. Indigenous peoples in present-day Canada include the First Nations, Métis, the last being a mixed-blood people who originated in the mid-17th century when First Nations and Inuit people married European settlers; the term "Aboriginal" as a collective noun is a specific term of art used in some legal documents, including the Constitution Act 1982. The first inhabitants of North America are hypothesized to have migrated from Siberia by way of the Bering land bridge and arrived at least 14,000 years ago; the Paleo-Indian archeological sites at Old Crow Flats and Bluefish Caves are two of the oldest sites of human habitation in Canada. The characteristics of Canadian indigenous societies included permanent settlements, complex societal hierarchies, trading networks; some of these cultures had collapsed by the time European explorers arrived in the late 15th and early 16th centuries and have only been discovered through archeological investigations.
The indigenous population at the time of the first European settlements is estimated to have been between 200,000
Amateur radio
Amateur radio known as ham radio, describes the use of radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport and emergency communication. The term "amateur" is used to specify "a duly authorised person interested in radioelectric practice with a purely personal aim and without pecuniary interest; the amateur radio service is established by the International Telecommunication Union through the Radio Regulations. National governments regulate technical and operational characteristics of transmissions and issue individual stations licenses with an identifying call sign. Prospective amateur operators are tested for their understanding of key concepts in electronics and the host government's radio regulations. Radio amateurs use a variety of voice, text and data communications modes and have access to frequency allocations throughout the RF spectrum; this enables communication across a city, country, the world, or into space.
In many countries, amateur radio operators may send, receive, or relay radio communications between computers or transceivers connected to secure virtual private networks on the Internet. Amateur radio is represented and coordinated by the International Amateur Radio Union, organized in three regions and has as its members the national amateur radio societies which exist in most countries. According to an estimate made in 2011 by the American Radio Relay League, two million people throughout the world are involved with amateur radio. About 830,000 amateur radio stations are located in IARU Region 2 followed by IARU Region 3 with about 750,000 stations. A smaller number, about 400,000, are located in IARU Region 1; the origins of amateur radio can be traced to the late 19th century, but amateur radio as practiced today began in the early 20th century. The First Annual Official Wireless Blue Book of the Wireless Association of America, produced in 1909, contains a list of amateur radio stations.
This radio callbook lists wireless telegraph stations in Canada and the United States, including 89 amateur radio stations. As with radio in general, amateur radio was associated with various amateur experimenters and hobbyists. Amateur radio enthusiasts have contributed to science, engineering and social services. Research by amateur operators has founded new industries, built economies, empowered nations, saved lives in times of emergency. Ham radio can be used in the classroom to teach English, map skills, math and computer skills; the term "ham" was first a pejorative term used in professional wired telegraphy during the 19th century, to mock operators with poor Morse code sending skills. This term continued to be used after the invention of radio and the proliferation of amateur experimentation with wireless telegraphy; the use of "ham" meaning "amateurish or unskilled" survives today in other disciplines. The amateur radio community subsequently began to reclaim the word as a label of pride, by the mid-20th century it had lost its pejorative meaning.
Although not an acronym, it is mistakenly written as "HAM" in capital letters. The many facets of amateur radio attract practitioners with a wide range of interests. Many amateurs begin with a fascination of radio communication and combine other personal interests to make pursuit of the hobby rewarding; some of the focal areas amateurs pursue include radio contesting, radio propagation study, public service communication, technical experimentation, computer networking. Amateur radio operators use various modes of transmission to communicate; the two most common modes for voice transmissions are single sideband. FM offers high quality audio signals, while SSB is better at long distance communication when bandwidth is restricted. Radiotelegraphy using Morse code known as "CW" from "continuous wave", is the wireless extension of landline telegraphy developed by Samuel Morse and dates to the earliest days of radio. Although computer-based modes and methods have replaced CW for commercial and military applications, many amateur radio operators still enjoy using the CW mode—particularly on the shortwave bands and for experimental work, such as earth-moon-earth communication, because of its inherent signal-to-noise ratio advantages.
Morse, using internationally agreed message encodings such as the Q code, enables communication between amateurs who speak different languages. It is popular with homebrewers and in particular with "QRP" or very-low-power enthusiasts, as CW-only transmitters are simpler to construct, the human ear-brain signal processing system can pull weak CW signals out of the noise where voice signals would be inaudible. A similar "legacy" mode popular with home constructors is amplitude modulation, pursued by many vintage amateur radio enthusiasts and aficionados of vacuum tube technology. Demonstrating a proficiency in Morse code was for many years a requirement to obtain an amateur license to transmit on frequencies below 30 MHz. Following changes in international regulations in 2003, countries are no longer required to demand proficiency; the United States Federal
AM broadcasting
AM broadcasting is a radio broadcasting technology, which employs amplitude modulation transmissions. It was the first method developed for making audio radio transmissions, is still used worldwide for medium wave transmissions, but on the longwave and shortwave radio bands; the earliest experimental AM transmissions began in the early 1900s. However, widespread AM broadcasting was not established until the 1920s, following the development of vacuum tube receivers and transmitters. AM radio remained the dominant method of broadcasting for the next 30 years, a period called the "Golden Age of Radio", until television broadcasting became widespread in the 1950s and received most of the programming carried by radio. Subsequently, AM radio's audiences have greatly shrunk due to competition from FM radio, Digital Audio Broadcasting, satellite radio, HD radio and Internet streaming. AM transmissions are much more susceptible than FM or digital signals are to interference, have lower audio fidelity.
Thus, AM broadcasters tend to specialise in spoken-word formats, such as talk radio, all news and sports, leaving the broadcasting of music to FM and digital stations. The idea of broadcasting — the unrestricted transmission of signals to a widespread audience — dates back to the founding period of radio development though the earliest radio transmissions known as "Hertzian radiation" and "wireless telegraphy", used spark-gap transmitters that could only transmit the dots-and-dashes of Morse code. In October 1898 a London publication, The Electrician, noted that "there are rare cases where, as Dr. Lodge once expressed it, it might be advantageous to'shout' the message, spreading it broadcast to receivers in all directions". However, it was recognized that this would involve significant financial issues, as that same year The Electrician commented "did not Prof. Lodge forget that no one wants to pay for shouting to the world on a system by which it would be impossible to prevent non-subscribers from benefiting gratuitously?"On January 1, 1902, Nathan Stubblefield gave a short-range "wireless telephone" demonstration, that included broadcasting speech and music to seven locations throughout Murray, Kentucky.
However, this was transmitted using induction rather than radio signals, although Stubblefield predicted that his system would be perfected so that "it will be possible to communicate with hundreds of homes at the same time", "a single message can be sent from a central station to all parts of the United States", he was unable to overcome the inherent distance limitations of this technology. The earliest public radiotelegraph broadcasts were provided as government services, beginning with daily time signals inaugurated on January 1, 1905, by a number of U. S. Navy stations. In Europe, signals transmitted from a station located on the Eiffel tower were received throughout much of Europe. In both the United States and France this led to a small market of receiver lines designed geared for jewelers who needed accurate time to set their clocks, including the Ondophone in France, the De Forest RS-100 Jewelers Time Receiver in the United States The ability to pick up time signal broadcasts, in addition to Morse code weather reports and news summaries attracted the interest of amateur radio enthusiasts.
It was recognized that, much like the telegraph had preceded the invention of the telephone, the ability to make audio radio transmissions would be a significant technical advance. Despite this knowledge, it still took two decades to perfect the technology needed to make quality audio transmissions. In addition, the telephone had been used for distributing entertainment, outside of a few "telephone newspaper" systems, most of which were established in Europe. With this in mind, most early radiotelephone development envisioned that the device would be more profitably developed as a "wireless telephone" for personal communication, or for providing links where regular telephone lines could not be run, rather than for the uncertain finances of broadcasting; the person credited as the primary early developer of AM technology is Canadian-born inventor Reginald Fessenden. The original spark-gap radio transmitters were impractical for transmitting audio, since they produced discontinuous pulses known as "damped waves".
Fessenden realized that what was needed was a new type of radio transmitter that produced steady "undamped" signals, which could be "modulated" to reflect the sounds being transmitted. Fessenden's basic approach was disclosed in U. S. Patent 706,737, which he applied for on May 29, 1901, was issued the next year, it called for the use of a high-speed alternator that generated "pure sine waves" and produced "a continuous train of radiant waves of uniform strength", or, in modern terminology, a continuous-wave transmitter. Fessenden began his research on audio transmissions while doing developmental work for the United States Weather Service on Cobb Island, Maryland; because he did not yet have a continuous-wave transmitter he worked with an experimental "high-frequency spark" transmitter, taking advantage of the fact that the higher the spark rate, the closer a spark-gap transmission comes to producing continuous waves. He reported that, in the fall of 1900, he transmitted speech over a distance of about 1.6 kilometers, which appears to have been the first successful audio transmission using radio signals.
However, at this time the sound was far too distorted to be commercially practical. For a time he continued working with more sophist
International Telecommunication Union
The International Telecommunication Union the International Telegraph Union, is a specialized agency of the United Nations, responsible for issues that concern information and communication technologies. It is the oldest among all the 15 specialised agencies of UN; the ITU coordinates the shared global use of the radio spectrum, promotes international cooperation in assigning satellite orbits, works to improve telecommunication infrastructure in the developing world, assists in the development and coordination of worldwide technical standards. The ITU is active in areas including broadband Internet, latest-generation wireless technologies and maritime navigation, radio astronomy, satellite-based meteorology, convergence in fixed-mobile phone, Internet access, voice, TV broadcasting, next-generation networks; the agency organizes worldwide and regional exhibitions and forums, such as ITU Telecom World, bringing together representatives of government and the telecommunications and ICT industry to exchange ideas and technology.
ITU, based in Geneva, Switzerland, is a member of the United Nations Development Group, has 12 regional and area offices in the world. ITU has been an intergovernmental public–private partnership organization since its inception, its membership includes 193 Member States and around 800 public and private sector companies, academic institutions as well as international and regional telecommunication entities, known as Sector Members and Associates, which undertake most of the work of each Sector. ITU was formed in Paris, at the International Telegraph Convention; the International Radiotelegraph Union was unofficially established at first International Radiotelegraph Convention in 1906. Both were merged into the International Telecommunication Union in 1932. ITU became a United Nations specialized agency in 1947; the ITU comprises three sectors, each managing a different aspect of the matters handled by the Union, as well as ITU Telecom. The sectors were created during the restructuring of ITU at its 1992 Plenipotentiary Conference.
Radio communication Established in 1927 as the International Radio Consultative Committee or CCIR, this sector manages the international radio-frequency spectrum and satellite orbit resources. In 1992, the CCIR became the ITU-R. Standardisation Standardisation was the original purpose of ITU since its inception. Established in 1956 as the International Telephone and Telegraph Consultative Committee or CCITT, this sector standardizes global telecommunications. In 1993, the CCITT became the ITU-T. Development Established in 1992, this sector helps spread equitable and affordable access to information and communication technologies. ITU Telecom ITU Telecom organizes major events for the world's ICT community. A permanent General Secretariat, headed by the Secretary General, manages the day-to-day work of the Union and its sectors; the basic texts of the ITU are adopted by the ITU Plenipotentiary Conference. The founding document of the ITU was the 1865 International Telegraph Convention, which has since been amended several times and is now entitled the "Constitution and Convention of the International Telecommunication Union".
In addition to the Constitution and Convention, the consolidated basic texts include the Optional Protocol on the settlement of disputes, the Decisions and Recommendations in force, as well as the General Rules of Conferences and Meetings of the Union. The ITU is headed by a Secretary-General, a Deputy Secretary General and the three directors of the Bureaux, who are elected to a four-year terms by the member states at the ITU Plenipotentiary Conference. On 23 October 2014 Houlin Zhao was elected 19th Secretary-General of the ITU at the Plenipotentiary Conference in Busan, Republic of Korea, his four-year mandate started on 1 January 2015, he was formally inaugurated on 15 January 2015. Houlin Zhao was reelected at the 2018 Plenipotentiary Conference in Dubai. Membership of ITU is open to only Member States of the United Nations, which may join the Union as Member States, as well as to private organizations like carriers, equipment manufacturers, funding bodies and development organizations and international and regional telecommunication organizations, which may join ITU as non-voting Sector Members.
There are 193 Member States of the ITU, including all UN member states except the Republic of Palau, plus the Vatican City. The most recent member state to join the ITU is South Sudan, which became a member on 14 July 2011; the Republic of China was blocked from membership by the People's Republic of China, but received a country code, being listed as "Taiwan, China". Palestine was admitted as an observer in 2010. Six Regional Offices and seven Area Offices guarantee a regional presence of ITU: Regional Office for CSI Africa Regional Office in Addis Ababa, with Area Offices in Dakar and Yaoundé Arab States Regional Office in Cairo Asia-Pacific Regional Office in Bangkok, with Area Office in Jakarta America Regional Office in Brasilia, with Area Offices in Bridgetown and Tegucigalpa; the sixth is a Coordination office for Europe Region Europe at ITU Headquarters. Other Regional organizations, connected to ITU, are: Asia-Pacific Telecommunity Arab Spectrum Management Group African Telecommunications Union European Conference of Posta
Single-sideband modulation
In radio communications, single-sideband modulation or single-sideband suppressed-carrier modulation is a type of modulation, used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modulation, it uses transmitter bandwidth more efficiently. Amplitude modulation produces an output signal the bandwidth of, twice the maximum frequency of the original baseband signal. Single-sideband modulation avoids this bandwidth increase, the power wasted on a carrier, at the cost of increased device complexity and more difficult tuning at the receiver. Radio transmitters work by mixing a radio frequency signal of a specific frequency, the carrier wave, with the audio signal to be broadcast. In AM transmitters this mixing takes place in the final RF amplifier, it is less common and much less efficient to do the mixing at low power and amplify it in a linear amplifier. Either method produces a set of frequencies with a strong signal at the carrier frequency and with weaker signals at frequencies extending above and below the carrier frequency by the maximum frequency of the input signal.
Thus the resulting signal has a spectrum whose bandwidth is twice the maximum frequency of the original input audio signal. SSB takes advantage of the fact that the entire original signal is encoded in each of these "sidebands", it is not necessary to transmit both sidebands plus the carrier, as a suitable receiver can extract the entire original signal from either the upper or lower sideband. There are several methods for eliminating the one sideband from the transmitted signal. Producing this single sideband signal is too complicated to be done in the final amplifier stage as with AM. SSB Modulation must be done at a low level and amplified in a linear amplifier where lower efficiency offsets the power advantage gained by eliminating the carrier and one sideband. SSB transmissions use the available amplifier energy more efficiently, providing longer-range transmission for the same power output. In addition, the occupied spectrum is less than half that of a full carrier AM signal. SSB reception requires frequency stability and selectivity well beyond that of inexpensive AM receivers, why broadcasters have used it.
In point to point communications where expensive receivers are in common use they can be adjusted to receive whichever sideband is being transmitted. The first U. S. patent application for SSB modulation was filed on December 1915 by John Renshaw Carson. The U. S. Navy experimented with SSB over its radio circuits before World War I. SSB first entered commercial service on January 7, 1927 on the longwave transatlantic public radiotelephone circuit between New York and London; the high power SSB transmitters were located at New York and Rugby, England. The receivers were in quiet locations in Houlton and Cupar Scotland. SSB was used over long distance telephone lines, as part of a technique known as frequency-division multiplexing. FDM was pioneered by telephone companies in the 1930s. With this technology, many simultaneous voice channels could be transmitted on a single physical circuit, for example in L-carrier. With SSB, channels could to be spaced only 4,000 Hz apart, while offering a speech bandwidth of nominally 300 Hz to 3,400 Hz.
Amateur radio operators began serious experimentation with SSB after World War II. The Strategic Air Command established SSB as the radio standard for its aircraft in 1957, it has become a de facto standard for long-distance voice radio transmissions since then. Single-sideband has the mathematical form of quadrature amplitude modulation in the special case where one of the baseband waveforms is derived from the other, instead of being independent messages: where s is the message, s ^ is its Hilbert transform, f 0 is the radio carrier frequency. To understand this formula, we may express s as the real part of a complex-valued function, with no loss of information: s = Re = Re , where j represents the imaginary unit. S a is the analytic representation of s, which means that it comprises only the positive-frequency components of s: 1 2 S a = { S, for f > 0, 0, for f < 0, {\displaystyle S_{\
