Height above average terrain
Height above average terrain, or effective height above average terrain, is a measure of how high an antenna site is above the surrounding landscape. HAAT is used extensively in FM radio and television, as it is more important than effective radiated power in determining the range of broadcasts. For international coordination, it is measured in meters by the Federal Communications Commission in the United States, as Canada and Mexico have extensive border zones where stations can be received on either side of the international boundaries. Stations that want to increase above a certain HAAT must reduce their power accordingly, based on the maximum distance their station class is allowed to cover; the FCC procedure to calculate HAAT is: from the proposed or actual antenna site, either 12 or 16 radials were drawn, points at 2, 4, 6, 8, 10 miles radius along each radial were used. The entire radial graph could be rotated to achieve the best effect for the station; the altitude of the antenna site, minus the average altitude of all the specified points, is the HAAT.
This can create some unusual cases in mountainous regions—it is possible to have a negative number for HAAT. The FCC has divided the Contiguous United States into three zones for the determination of spacing between FM and TV stations using the same frequencies. FM and TV stations are assigned maximum ERP and HAAT values, depending on their assigned zones, to prevent co-channel interference; the FCC regulations for ERP and HAAT are listed under Title 47, Part 73 of the Code of Federal Regulations. Maximum HAAT: 150 metres Maximum ERP: 50 kilowatts Minimum co-channel separation: 241 km Maximum HAAT: 600 metres Maximum ERP: 100 kilowatts Minimum co-channel separation: 290 km. In all zones, maximum ERP for analog TV transmitters is. In addition, Zone I-A consists of all of California south of 40° north latitude, Puerto Rico and the U. S. Virgin Islands. Zones I and I-A have the most "grandfathered" overpowered stations, which are allowed the same extended coverage areas that they had before the zones were established.
One of the most powerful of these stations is WBCT in Grand Rapids, which operates at 320,000 watts and 238 meters HAAT. Zone III consists of all of Florida and the areas of Alabama, Louisiana and Texas within 241.4 kilometers of the Gulf of Mexico. Zone II is all the rest of the Continental United States and Hawaii. Above mean sea level Above ground level Canadian Radio-television and Telecommunications Commission List of broadcast station classes United States Federal Communications Commission 47 CFR Part 73 Index FCC: Mass Media Calculated Contours FCC: HAAT Calculator "Superpower" Grandfathered FM stations
Very high frequency
High frequency is the ITU designation for the range of radio frequency electromagnetic waves from 30 to 300 megahertz, with corresponding wavelengths of ten meters to one meter. Frequencies below VHF are denoted high frequency, the next higher frequencies are known as ultra high frequency. Common uses for radio waves in the VHF band are FM radio broadcasting, television broadcasting, two way land mobile radio systems, long range data communication up to several tens of kilometers with radio modems, amateur radio, marine communications. Air traffic control communications and air navigation systems work at distances of 100 kilometres or more to aircraft at cruising altitude. In the Americas and many other parts of the world, VHF Band I was used for the transmission of analog television; as part of the worldwide transition to digital terrestrial television most countries require broadcasters to air television in the VHF range using digital rather than analog format. Radio waves in the VHF band propagate by line-of-sight and ground-bounce paths.
They do not follow the contour of the Earth as ground waves and so are blocked by hills and mountains, although because they are weakly refracted by the atmosphere they can travel somewhat beyond the visual horizon out to about 160 km. They can penetrate building walls and be received indoors, although in urban areas reflections from buildings cause multipath propagation, which can interfere with television reception. Atmospheric radio noise and interference from electrical equipment is less of a problem in the band than at lower frequencies; the VHF band is the first band at which efficient transmitting antennas are small enough that they can be mounted on vehicles and portable devices, so the band is used for two-way land mobile radio systems, such as walkie-talkies, two way radio communication with aircraft and ships. When conditions are right, VHF waves can travel long distances by tropospheric ducting due to refraction by temperature gradients in the atmosphere. For analog TV, VHF transmission range is a function of transmitter power, receiver sensitivity, distance to the horizon, since VHF signals propagate under normal conditions as a near line-of-sight phenomenon.
The distance to the radio horizon is extended over the geometric line of sight to the horizon, as radio waves are weakly bent back toward the Earth by the atmosphere. An approximation to calculate the line-of-sight horizon distance is: distance in nautical miles = 1.23 × A f where A f is the height of the antenna in feet distance in kilometers = 12.746 × A m where A m is the height of the antenna in meters. These approximations are only valid for antennas at heights that are small compared to the radius of the Earth, they may not be accurate in mountainous areas, since the landscape may not be transparent enough for radio waves. In engineered communications systems, more complex calculations are required to assess the probable coverage area of a proposed transmitter station; the accuracy of these calculations for digital TV signals is being debated. VHF is the first band at which wavelengths are small enough that efficient transmitting antennas are short enough to mount on vehicles and handheld devices, a quarter wave whip antenna at VHF frequencies is 25 cm to 2.5 meter long.
So the VHF and UHF wavelengths are used for two-way radios in vehicles and handheld transceivers and walkie-talkies. Portable radios use whips or rubber ducky antennas, while base stations use larger fiberglass whips or collinear arrays of vertical dipoles. For directional antennas, the Yagi antenna is the most used as a high gain or "beam" antenna. For television reception, the Yagi is used, as well as the log-periodic antenna due to its wider bandwidth. Helical and turnstile antennas are used for satellite communication since they employ circular polarization. For higher gain, multiple Yagis or helicals can be mounted together to make array antennas. Vertical collinear arrays of dipoles can be used to make high gain omnidirectional antennas, in which more of the antenna's power is radiated in horizontal directions. Television and FM broadcasting stations use collinear arrays of specialized dipole antennas such as batwing antennas. Certain subparts of the VHF band have the same use around the world.
Some national uses are detailed below. 50–54 MHz: Amateur Radio 6-meter band. 108–118 MHz: Air navigation beacons VOR and Instrument Landing System localizer. 118–137 MHz: Airband for air traffic control, AM, 121.5 MHz is emergency frequency 144–148 MHz: Amateur Radio 2-meter band. The VHF TV band in Australia was allocated channels 1 to 10-with channels 2, 7 and 9 assigned for the initial services in Sydney and Melbourne, the same channels were assigned in Brisbane and Perth. Other capital cities and regional areas used a combination of these and other frequencies as available; the initial commercial services in Hobart and Darwin were allocated channels 6 and 8 rather than 7 or 9. By the early 1960s it became apparent that the 10 VHF channels were insufficient to support the growth of television services; this was rectified by the addition of th
A television station is a set of equipment managed by a business, organisation or other entity, such as an amateur television operator, that transmits video content via radio waves directly from a transmitter on the earth's surface to a receiver on earth. Most the term refers to a station which broadcasts structured content to an audience or it refers to the organization that operates the station. A terrestrial television transmission can occur via analog television signals or, more via digital television signals. Television stations are differentiated from cable television or other video providers in that their content is broadcast via terrestrial radio waves. A group of television stations with common ownership or affiliation are known as a TV network and an individual station within the network is referred to as O&O or affiliate, respectively; because television station signals use the electromagnetic spectrum, which in the past has been a common, scarce resource, governments claim authority to regulate them.
Broadcast television systems standards vary around the world. Television stations broadcasting over an analog system were limited to one television channel, but digital television enables broadcasting via subchannels as well. Television stations require a broadcast license from a government agency which sets the requirements and limitations on the station. In the United States, for example, a television license defines the broadcast range, or geographic area, that the station is limited to, allocates the broadcast frequency of the radio spectrum for that station's transmissions, sets limits on what types of television programs can be programmed for broadcast and requires a station to broadcast a minimum amount of certain programs types, such as public affairs messages. Another form a television station may take is non-commercial educational and considered public broadcasting. To avoid concentration of media ownership of television stations, government regulations in most countries limit the ownership of television stations by television networks or other media operators, but these regulations vary considerably.
Some countries have set up nationwide television networks, in which individual television stations act as mere repeaters of nationwide programs. In those countries, the local television station has no station identification and, from a consumer's point of view, there is no practical distinction between a network and a station, with only small regional changes in programming, such as local television news. To broadcast its programs, a television station requires operators to operate equipment, a transmitter or radio antenna, located at the highest point available in the transmission area, such as on a summit, the top of a high skyscraper, or on a tall radio tower. To get a signal from the master control room to the transmitter, a studio/transmitter link is used; the link can be either by radio or T1/E1. A transmitter/studio link may send telemetry back to the station, but this may be embedded in subcarriers of the main broadcast. Stations which retransmit or simulcast another may pick-up that station over-the-air, or via STL or satellite.
The license specifies which other station it is allowed to carry. VHF stations have tall antennas due to their long wavelength, but require much less effective radiated power, therefore use much less transmitter power output saving on the electricity bill and emergency backup generators. In North America, full-power stations on band I are limited to 100 kW analog video and 10 kW analog audio, or 45 kW digital ERP. Stations on band III can go up by 31.6 kW audio, or 160 kW digital. Low-VHF stations are subject to long-distance reception just as with FM. There are no stations on Channel 1. UHF, by comparison, has a much shorter wavelength, thus requires a shorter antenna, but higher power. North American stations can go up to 5000 1000 kW digital. Low channels travel further than high ones at the same power, but UHF does not suffer from as much electromagnetic interference and background "noise" as VHF, making it much more desirable for TV. Despite this, in the U. S. the Federal Communications Commission is taking another large portion of this band away, in contrast to the rest of the world, taking VHF instead.
This means. Since at least 1974, there are no stations on channel 37 in North America for radio astronomy purposes. Most television stations are commercial broadcasting enterprises which are structured in a variety of ways to generate revenue from television commercials, they may be some other structure. They can produce some or all of their programs or buy some broadcast syndication programming for or all of it from other stations or independent production companies. Many stations have some sort of television studio, which on major-network stations is used for newscasts or other local programming. There is a news department, where journalists gather information. There is a section where electronic news-gathering operations are based, receiving remote broadcasts via remote pickup unit or satellite TV. Outside broadcasting vans, production trucks, or SUVs with electronic field production equipment are sent out with reporters, who may bring back news stories on video tape rather than sending them back live.
To keep pace with technology United States television stations have been replacing operators with broadcast automation systems to increas
Digital terrestrial television
Digital terrestrial television is a technology for broadcast television in which land-based television stations broadcast television content by radio waves to televisions in consumers' residences in a digital format. DTTV is a major technological advance over the previous analog television, has replaced analog, in common use since the middle of the 20th century. Test broadcasts began in 1998 with the changeover to DTTV beginning in 2006 and is now complete in many countries; the advantages of digital terrestrial television are similar to those obtained by digitising platforms such as cable TV, telecommunications: more efficient use of limited radio spectrum bandwidth, provision of more television channels than analog, better quality images, lower operating costs for broadcasters. Different countries have adopted different digital broadcasting standards; the amount of data that can be transmitted is directly affected by channel capacity and the modulation method of the transmission. North America uses the ATSC standard with 8VSB modulation, which has similar characteristics to the vestigial sideband modulation used for analog television.
This provides more immunity to interference, but is not immune to multipath distortion and does not provide for single-frequency network operation. The modulation method in DVB-T is COFDM with either 16-state Quadrature Amplitude Modulation. In general, 64QAM is capable of transmitting a greater bit rate, but is more susceptible to interference. 16 and 64QAM constellations can be combined in a single multiplex, providing a controllable degradation for more important program streams. This is called hierarchical modulation. DVB-T are designed to work in single frequency networks. Developments in video compression have resulted in improvements on the original H.262 MPEG 2 codec, surpassed by H.264/MPEG-4 AVC and more H.265 HEVC. H.264 enables three high-definition television services to be coded into a 24 Mbit/s DVB-T European terrestrial transmission channel. DVB-T2 increases this channel capacity to 40 Mbit/s, allowing more services. DTTV is received either via a digital set-top box, TV gateway or more now an integrated tuner included with television sets, that decodes the signal received via a standard television antenna.
These devices now include digital video recorder functionality. However, due to frequency planning issues, an aerial capable of receiving a different channel group may be required if the DTTV multiplexes lie outside the reception capabilities of the installed aerial; this is quite common in the UK. Indoor aerials are more to be affected by these issues and need replacing. Main articles: List of digital television deployments by country, Digital television transition Afghanistan launched digital transmissions in Kabul using DVB-T2/MPEG-4 on Sunday, 31 August 2014. Test transmissions had commenced on 4 UHF channels at the start of June 2014. Transmitters were provided by GatesAir. Bangladesh had its first DTT service DVB-T2 / MPEG-4 on April 2016 launched by the GS Group; the service is called RealVU. It is done with partnership with Beximco. GS Group acts as a supplier and integrator of its in-house hardware and software solutions for the operator's functioning in accordance with the modern standards of digital television.
RealVu provides more than 100 TV channels in HD quality. The digital TV set-top boxes developed by GS Group offer such functions as PVR and time-shift, along with an EPG. India adopted DVB-T system for digital television in July 1999; the first DVB-T transmission was started on 26 January 2003 in the four major metropolitan cities by Doordarshan. The terrestrial transmission is available in both digital and analog formats. 4 high power DVB-T transmitters were set up in the top 4 cities, which were upgraded to DVB-T2 + MPEG4 and DVB-H standards. An additional 190 high power, 400 low power DVB-T2 transmitters have been approved for Tier I, II and III cities of the country by 2017; the Indian telecom regulator, TRAI, had recommended the I&B to allow private broadcast companies to use the DTT technology, in 2005. So far, the Indian I&B ministry only permits private broadcast companies to use satellite, cable and IPTV based systems; the government's broadcasting organisation Doordarshan had started the free TV service over DVB - T2 to the mobile phone users from February 25 onwards and extended to cover 16 cities including the four metros from April 5, 2016.
Israel started digital transmissions in MPEG-4 on Sunday, August 2, 2009, anal
AT&T U-verse called U-verse, is an AT&T brand of triple-play telecommunications services, although the brand is now only used in reference to the IPTV service. Launched on June 26, 2006, U-verse included broadband Internet, IP telephone, IPTV services in 21 states. In September 2016, AT&T announced that the "U-verse" brand would no longer apply to its broadband and phone services, renaming them "AT&T Internet" and "AT&T Phone", respectively. SBC announced its plans for a fiber-optic network and Internet Protocol television deployment in 2004 and unveiled the name "U-verse" for the suite of network services in 2005. Beta testing began in San Antonio in 2005 and AT&T U-verse was commercially launched June 26, 2006, in San Antonio. A few months on November 30, 2006, the service was launched in Houston. In December 2006, the product launched in Chicago, San Francisco, Hartford and other cities in their vicinities. In February 2007, U-verse was launched in Milwaukee. One month service was initiated in Dallas and Kansas City.
In May 2007, U-verse launched in Detroit, Los Angeles, surrounding areas. Launch continued in Cleveland and San Diego in June 2007; the Oklahoma City and Sacramento launches occurred in August 2007. In November 2007, service was started in Austin. In December 2007, U-verse was launched in St. Louis. A controlled launch was initiated in Atlanta that month marking the first launch in the Southeastern United States. On December 22, 2008, the product debuted in Birmingham. On January 25, 2010, AT&T announced. AT&T Phone was added on January 22, 2008, was first available in Detroit. In 2008, U-verse availability approached 8 million households and over 225,000 customers had been enrolled, with new installations reaching 12,000 per week. By 2009, 1 million Phone customers and 2.1 million U-verse TV customers had been enrolled. At the end of 2011, U-verse was available to more than 30 million living units in 22 states and U-verse TV had 3.8 million customers. By mid-2012, AT&T had 4.1 million U-Verse TV subscribers, 2.6 million Phone subscribers, 6.5 million Internet subscribers.
By the third quarter of 2012, AT&T had 4.3 million TV subscribers, 2.7 million Phone subscribers and 7.1 million Internet. This represents 7% growth quarter on quarter; the actual number of customers is lower, as most customers subscribe to a bundle and so are counted in both categories. At an analyst meeting in August 2015, following AT&T's acquisition of satellite provider DirecTV, AT&T announced plans for a new "home entertainment gateway" platform that will converge DirecTV and U-verse around a common platform based upon DirecTV hardware with "very thin hardware profiles". AT&T Entertainment and Internet Services CEO John Stankey explained that the new platform would offer "single truck roll installation for multiple products, live local streaming, improved content portability, over-the-top integration for mobile broadband, user interface re-engineering."In February 2016, Bloomberg reported that AT&T was in the process of phasing out the U-verse IPTV service by encouraging new customers to purchase DirecTV satellite service instead, by ending the production of new set-top boxes for the service.
An AT&T spokesperson denied that U-verse was being shut down and explained that the company was "leading its video marketing approach with DirecTV" to "realize the many benefits" of the purchase, but would still recommend U-verse TV if it better-suited a customer's needs. AT&T CFO John Stephens had previously stated that DirecTV's larger subscriber base as a national service gave the service a higher degree of leverage in negotiating carriage deals, thus resulting in lower content costs. On March 29, 2016, AT&T announced that it will increase data caps on its Internet service on May 23, 2016; the integration of AT&T and DirecTV is set to begin by the fourth quarter of 2016. On May 16, 2016, AT&T announced that it will acquire Quickplay Media, a cloud-based platform that powers over-the-top video services. On September 19, 2016, AT&T announced that the "U-verse" brand would no longer apply to its broadband and phone services, renaming them "AT&T Internet" and "AT&T Phone", respectively. On October 4, 2016, it was reported that AT&T had adopted "AT&T Fiber" as the new brand name for its fiber-based internet service, with the "AT&T Internet" brand continuing to be used for its DSL internet service.
On April 25, 2017, it was reported. On March 13, 2018, it was reported that AT&T has filed a trademark for "AT&T TV" with the U. S. Patent & Trademark Office, a possible signal that the telco company will eliminate its current brand names DirecTV and U-verse. AT&T delivers most U-verse service over a fiber-to-the-node or fiber-to-the-premises communications network. In the more common FTTN deployment, fiber-optic connections carry all data between the service provider and a distribution node; the remaining run from the node to the network interface device in the customer's home uses a copper-wire current loop, traditionally part of the PSTN. In more constructed housing developments, AT&T uses an FTTP deployment—they run fiber-optic cable from their DSLAM all the way to an optical network terminal in the customer's home. In areas where AT&T deploys U-verse through FTTN, they use High-speed digital subscriber lines with ADSL2+ or VDSL technology. Service offerings depend on the customer's distance to an available port in the distribution node, or the centra
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government created by statute to regulate interstate communications by radio, wire and cable. The FCC serves the public in the areas of broadband access, fair competition, radio frequency use, media responsibility, public safety, homeland security; the FCC was formed by the Communications Act of 1934 to replace the radio regulation functions of the Federal Radio Commission. The FCC took over wire communication regulation from the Interstate Commerce Commission; the FCC's mandated jurisdiction covers the 50 states, the District of Columbia, the Territories of the United States. The FCC provides varied degrees of cooperation and leadership for similar communications bodies in other countries of North America; the FCC is funded by regulatory fees. It has an estimated fiscal-2016 budget of US $388 million, it has 1,688 federal employees, made up of 50% males and 50% females as of December, 2017. The FCC's mission, specified in Section One of the Communications Act of 1934 and amended by the Telecommunications Act of 1996 is to "make available so far as possible, to all the people of the United States, without discrimination on the basis of race, religion, national origin, or sex, efficient and world-wide wire and radio communication services with adequate facilities at reasonable charges."
The Act furthermore provides that the FCC was created "for the purpose of the national defense" and "for the purpose of promoting safety of life and property through the use of wire and radio communications."Consistent with the objectives of the Act as well as the 1999 Government Performance and Results Act, the FCC has identified four goals in its 2018-22 Strategic Plan. They are: Closing the Digital Divide, Promoting Innovation, Protecting Consumers & Public Safety, Reforming the FCC's Processes; the FCC is directed by five commissioners appointed by the President of the United States and confirmed by the United States Senate for five-year terms, except when filling an unexpired term. The U. S. President designates one of the commissioners to serve as chairman. Only three commissioners may be members of the same political party. None of them may have a financial interest in any FCC-related business. † Commissioners may continue serving until the appointment of their replacements. However, they may not serve beyond the end of the next session of Congress following term expiration.
In practice, this means that commissioners may serve up to 1 1/2 years beyond the official term expiration dates listed above if no replacement is appointed. This would end on the date that Congress adjourns its annual session no than noon on January 4; the FCC is organized into seven Bureaus, which process applications for licenses and other filings, analyze complaints, conduct investigations and implement regulations, participate in hearings. The Consumer & Governmental Affairs Bureau develops and implements the FCC's consumer policies, including disability access. CGB serves as the public face of the FCC through outreach and education, as well as through their Consumer Center, responsible for responding to consumer inquiries and complaints. CGB maintains collaborative partnerships with state and tribal governments in such areas as emergency preparedness and implementation of new technologies; the Enforcement Bureau is responsible for enforcement of provisions of the Communications Act 1934, FCC rules, FCC orders, terms and conditions of station authorizations.
Major areas of enforcement that are handled by the Enforcement Bureau are consumer protection, local competition, public safety, homeland security. The International Bureau develops international policies in telecommunications, such as coordination of frequency allocation and orbital assignments so as to minimize cases of international electromagnetic interference involving U. S. licensees. The International Bureau oversees FCC compliance with the international Radio Regulations and other international agreements; the Media Bureau develops and administers the policy and licensing programs relating to electronic media, including cable television, broadcast television, radio in the United States and its territories. The Media Bureau handles post-licensing matters regarding direct broadcast satellite service; the Wireless Telecommunications Bureau regulates domestic wireless telecommunications programs and policies, including licensing. The bureau implements competitive bidding for spectrum auctions and regulates wireless communications services including mobile phones, public safety, other commercial and private radio services.
The Wireline Competition Bureau develops policy concerning wire line telecommunications. The Wireline Competition Bureau's main objective is to promote growth and economical investments in wireline technology infrastructure, development and services; the Public Safety and Homeland Security Bureau was launched in 2006 with a focus on critical communications infrastructure. The FCC has eleven Staff Offices; the FCC's Offices provide support services to the Bureaus. The Office of Administrative Law Judges is responsible for conducting hearings ordered by the Commission; the hearing function includes acting on interlocutory requests filed in the proceedings such as petitions to intervene, petitions to enlarge issues, contested discovery requests. An Administrative Law Judge, appointed under the Administrative Procedure Act, presides at the hearing during which documents and sworn testimony are received in evidence, witnesses are cross-examined. At the co
In broadcasting and radio communications, a call sign is a unique designation for a transmitter station. In the United States of America, they are used for all FCC-licensed transmitters. A call sign can be formally assigned by a government agency, informally adopted by individuals or organizations, or cryptographically encoded to disguise a station's identity; the use of call signs as unique identifiers dates to the landline railroad telegraph system. Because there was only one telegraph line linking all railroad stations, there needed to be a way to address each one when sending a telegram. In order to save time, two-letter identifiers were adopted for this purpose; this pattern continued in radiotelegraph operation. These were not globally unique, so a one-letter company identifier was added. By 1912, the need to identify stations operated by multiple companies in multiple nations required an international standard. Merchant and naval vessels are assigned call signs by their national licensing authorities.
In the case of states such as Liberia or Panama, which are flags of convenience for ship registration, call signs for larger vessels consist of the national prefix plus three letters. United States merchant vessels are given call signs beginning with the letters "W" or "K" while US naval ships are assigned call signs beginning with "N". Both ships and broadcast stations were assigned call signs in this series consisting of three or four letters. Ships equipped with Morse code radiotelegraphy, or life boat radio sets, Aviation ground stations, broadcast stations were given four letter call signs. Maritime coast stations on high frequency were assigned three letter call signs; as demand for both marine radio and broadcast call signs grew American-flagged vessels with radiotelephony only were given longer call signs with mixed letters and numbers. Leisure craft with VHF radios may not be assigned call signs, in which case the name of the vessel is used instead. Ships in the US still wishing to have a radio license are under FCC class SA: "Ship recreational or voluntarily equipped."
Those calls follow the land mobile format of the initial letter K or W followed by 1 or 2 letters followed by 3 or 4 numbers. U. S. Coast Guard small boats have a number, shown on both bows in which the first two digits indicate the nominal length of the boat in feet. For example, Coast Guard 47021 refers to the 21st in the series of 47-foot motor lifeboats; the call sign might be abbreviated to the final two or three numbers during operations, for example: Coast Guard zero two one. Aviation mobile stations equipped with radiotelegraphy were assigned five letter call signs.. Land Stations in Aviation were assigned four letter call signs; these call signs were phased out in the 1960s when flight radio officers were no longer required on international flights. USSR kept FRO's for the Moscow-Havana run until around 2000. All signs in aviation are derived from several different policies, depending upon the type of flight operation and whether or not the caller is in an aircraft or at a ground facility.
In most countries, unscheduled general aviation flights identify themselves using the call sign corresponding to the aircraft's registration number. In this case, the call sign is spoken using the International Civil Aviation Organization phonetic alphabet. Aircraft registration numbers internationally follow the pattern of a country prefix, followed by a unique identifier made up of letters and numbers. For example, an aircraft registered as N978CP conducting a general aviation flight would use the call sign November-niner-seven-eight-Charlie-Papa. However, in the United States a pilot of an aircraft would omit saying November, instead use the name of the aircraft manufacturer or the specific model. At times, general aviation pilots might omit additional preceding numbers and use only the last three numbers and letters; this is true at uncontrolled fields when reporting traffic pattern positions or at towered airports after establishing two-way communication with the tower controller. For example, Skyhawk eight-Charlie-Papa, left base.
In most countries, the aircraft call sign or "tail number"/"tail letters" are linked to the international radio call sign allocation table and follow a convention that aircraft radio stations receive call signs consisting of five letters. For example, all British civil aircraft have a five-letter call sign beginning with the letter G. Canadian aircraft have a call sign beginning with C–F or C–G, such as C–FABC. Wing In Ground-effect vehicles in Canada are eligible to receive C–Hxxx call signs, ultralight aircraft receive C-Ixxx call signs. In days gone by American aircraft used five letter call signs, such as KH–ABC, but they were replaced prior to World War II by the current American system of civilian aircraft call signs. Radio call signs used for communication in manned spaceflight is not formalized or regulated to the same degree as for aircraft; the three nations curren