Misplaced Pages

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95-561: APRS data is typically transmitted on a single shared frequency (depending on country) to be repeated locally by area relay stations (digipeaters) for widespread local consumption. In addition, all such data are typically ingested into the APRS Internet System (APRS-IS) via an Internet-connected receiver (IGate) and distributed globally for ubiquitous and immediate access. Data shared via radio or Internet are collected by all users and can be combined with external map data to build

190-637: 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 normally omit saying November , and 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 especially true at uncontrolled fields (those without control towers) when reporting traffic pattern positions or at towered airports after establishing two-way communication with

285-403: 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 (signal strength or power flux density in watts per square meter) as the actual source antenna at a distant receiver located in the direction of the antenna's strongest beam ( main lobe ). ERP measures the combination of the power emitted by

380-497: A waiver , and can exceed normal restrictions. For most microwave systems, a completely non-directional isotropic antenna (one which radiates equally and perfectly well in every direction – a physical impossibility) is used as a reference antenna, and then one speaks of EIRP (effective isotropic radiated power) rather than ERP. This includes satellite transponders , radar, and other systems which use microwave dishes and reflectors rather than dipole-style antennas. In

475-548: A Great Britain call sign prefix, 90 and MGY to commemorate the 90th anniversary of historic 1912 radio distress calls from MGY , the Marconi station aboard the famed White Star luxury liner RMS Titanic ). The late King Hussein of Jordan was issued a special amateur license number, JY1 , which would have been the shortest possible call sign issued by the Hashemite Kingdom of Jordan. When identifying

570-468: A call sign for broadcast stations; however, they are still required for broadcasters in many countries, including the United States. Mobile phone services do not use call signs on-air because the phones and their users are not licensed, instead the cell operator is the one holding the license. However, the U.S. still assigns a call sign to each mobile-phone spectrum license. In the United States, voluntary ships operating domestically are not required to have

665-425: A call sign or license to operate VHF radios , radar or an EPIRB . Voluntary ships (mostly pleasure and recreational) are not required to have a radio. However, ships which are required to have radio equipment (most large commercial vessels) are issued a call sign. A directory of radio station call signs is called a callbook. Callbooks were originally bound books that resembled a telephone directory and contained

760-622: A cellular telephone tower has a fixed linear polarization, but the mobile handset must function well at any arbitrary orientation. Therefore, a handset design might provide dual polarization receive on the handset so that captured energy is maximized regardless of orientation, or the designer might use a circularly polarized antenna and account for the extra 3 dB of loss with amplification. For example, an FM radio station which advertises that it has 100,000 watts of power actually has 100,000 watts ERP, and not an actual 100,000-watt transmitter. The transmitter power output (TPO) of such

855-402: A certain number of digipeaters — or hops — depending upon the all-important "PATH" setting. Digipeaters keep track of the packets they forward for a period of time, thus preventing duplicate packets from being retransmitted. This keeps packets from circulating in endless loops inside the ad hoc network. Eventually, most packets are heard by an APRS Internet Gateway, called an IGate, and

950-690: A convention that aircraft radio stations (and, by extension, the aircraft itself) receive call signs consisting of five letters. For example, all British civil aircraft have a five-letter registration beginning with the letter G, which can also serve for a call sign. Canadian aircraft have a call sign beginning with C–F or C–G, such as C–FABC. wing-in-ground-effect vehicles and hovercraft in Canada are eligible to receive C–Hxxx call signs, and ultralight aircraft receive C-Ixxx call signs. In days gone by, even American aircraft used five-letter call signs, such as KH–ABC, but they were replaced prior to World War II by

1045-406: A few times a day, but this practice is becoming very rare. Argentinian broadcast call signs consist of two or three letters followed by multiple numbers, the second and third letters indicating region. In Brazil, radio and TV stations are identified by a ZY, a third letter and three numbers. ZYA and ZYB are allocated to television stations; ZYI , ZYJ , ZYL , and ZYK designate AM stations; ZYG

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1140-464: A gain of 1× (equiv. 0 dBi). So ERP and EIRP are measures of radiated power that can compare different combinations of transmitters and antennas on an equal basis. In spite of the names, ERP and EIRP do not measure transmitter power, or total power radiated by the antenna, they are just a measure of signal strength along the main lobe. They give no information about power radiated in other directions, or total power. ERP and EIRP are always greater than

1235-457: A geographical area, class of license, or identify a licensee as a visitor or temporary resident), and a 1-, 2-, or 3-letter suffix. In Australia, call signs are structured with a two letter prefix, a digit (which identifies geographical area), and a 2, 3 or 4 letter suffix. This suffix may be followed by a further suffix, or personal identifier, such as /P (portable), /M (mobile), /AM (aeronautical mobile) or /MM (maritime mobile). The number following

1330-699: A new, more efficient path of WIDE1-1,WIDE2-1. Testing radio range is often a large component of these hobbies. Amateur radio is often used with packet radio to communicate at 1200 baud, using the Automatic Packet Reporting System back to the ground station. Smaller packages called micro or pico trackers are also built and run under smaller balloons. These smaller trackers have used Morse code, Field Hell, and RTTY to transmit their locations and other data. The APRS protocol has been adapted and extended to support projects not directly related to its original purpose. The most notable of these are

1425-575: A number of databases connected to the APRS-IS allow Web-based access to the data as well as more advanced data-mining capabilities. A number of low-Earth orbiting satellites , including the International Space Station , are capable of relaying APRS data. An APRS infrastructure comprises a variety of Terminal Node Controller (TNC) equipment put in place by individual amateur radio operators. This includes sound cards interfacing

1520-463: A one-letter company identifier (for instance, 'M' and two letters as a Marconi station ) was later added. By 1912, the need to quickly identify stations operated by multiple companies in multiple nations required an international standard ; an ITU prefix would be used to identify a country, and the rest of the call sign an individual station in that country. Merchant and naval vessels are assigned call signs by their national licensing authorities. In

1615-438: A packet being lost, this is not the case, because the packets are transmitted (broadcast) to everyone and multiplied many times over by each digipeater. This means that all digipeaters and stations in range get a copy, and then proceed to broadcast it to all other digipeaters and stations within their range. The result is that packets are multiplied more than they are lost. Therefore, packets can sometimes be heard some distance from

1710-451: A packet with a path of WIDE2-2 would be repeated through the first station as WIDE2-2, but the path will be modified (decremented) to WIDE2-1 for the next station to repeat. The packet stops being repeated when the "-N" portion of the path reaches "-0." This new protocol has caused the old RELAY and WIDE paths to become obsolete. Digi operators are being asked to re-configure fill-in "RELAY" stations to instead respond to WIDE1-1. This results in

1805-447: A path of RELAY,WIDE for reporting stations. However, there was no duplicate packet checking or alias substitution. This sometimes caused beacons to "ping pong" back and forth instead of propagating outwards from the source. This caused much interference. With no alias substitution, one could not tell which digipeaters a beacon had used. With the advent of the new "smart" TNCs, the stations that used to be "WIDE" became "WIDEn-N." This means

1900-818: A path of WIDE2-2 or less should be used as requirements dictate. The path parameter reflects the routing of packets via the radio component of APRS, and fixed stations should carefully consider their choice of path routing. Any path selection for stations that do not require it contributes to congestion of the APRS frequency and may hinder other stations' reporting. Aircraft and balloon APRS stations should avoid beaconing with any path at altitude since digipeating may not be necessary due to their antenna height and likelihood of reaching multiple wide-ranging digipeaters and IGates. Mobile stations in congested areas or more populated areas may consider using only 1 hop (WIDE1-1), as there are usually enough Internet gateways nearby that no path routing

1995-425: A radio to a computer, simple TNCs, and "smart" TNCs. The "smart" TNCs are capable of determining what has already happened with the packet and can prevent redundant packet repeating within the network. Reporting stations use a method of routing called a "path" to broadcast the information through a network. In a typical packet network, a station would use a path of known stations such as "via n8xxx,n8ary." This causes

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2090-680: A shared live view. APRS was developed from the late 1980s forward by Bob Bruninga, call sign WB4APR, a senior research engineer at the United States Naval Academy . He maintained the main APRS Web site until his death in 2022. The initialism "APRS" was derived from his call sign. Bob Bruninga, a senior research engineer at the United States Naval Academy, implemented the earliest ancestor of APRS on an Apple II computer in 1982. This early version

2185-484: A similar brand, and the name of a broadcast station for legal purposes is normally its internationally recognised ITU call sign. Some common conventions are followed in each country. Broadcast stations in North America generally use call signs in the international series. In the United States of America, they are used for all FCC-licensed transmitters. The first letter generally is K for stations located west of

2280-521: A station by voice, the call sign may be given by simply stating the letters and numbers, or using a phonetic alphabet . Some countries mandate the use of the phonetic alphabet for identification. In wartime, monitoring an adversary's communications can be a valuable form of intelligence. Consistent call signs can aid in this monitoring, so in wartime, military units often employ tactical call signs and sometimes change them at regular intervals. In peacetime, some military stations will use fixed call signs in

2375-423: A station typically may be 10,000–20,000 watts, with a gain factor of 5–10× (5–10×, or 7–10  dB ). In most antenna designs, gain is realized primarily by concentrating power toward the horizontal plane and suppressing it at upward and downward angles, through the use of phased arrays of antenna elements. The distribution of power versus elevation angle is known as the vertical pattern . When an antenna

2470-557: 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; radio companies initially assigned two-letter identifiers to coastal stations and stations on board ships at sea. These were not globally unique, so

2565-886: A theoretical isotropic antenna. Since a half-wave dipole antenna has a gain of 1.64 (or 2.15 dB ) compared to an isotropic radiator, if ERP and EIRP are expressed in watts their relation is   E I R P ( W ) = 1.64 × E R P ( W )   {\displaystyle \ {\mathsf {EIRP}}_{\mathsf {(W)}}=1.64\times {\mathsf {ERP}}_{\mathsf {(W)}}\ } If they are expressed in decibels   E I R P ( d B ) = E R P ( d B ) + 2.15   d B   {\displaystyle \ {\mathsf {EIRP}}_{\mathrm {(dB)} }={\mathsf {ERP}}_{\mathrm {(dB)} }+2.15\ {\mathsf {dB}}\ } Effective radiated power and effective isotropic radiated power both measure

2660-412: A wide variety of data, including weather reports, short text messages, radio direction finding bearings, telemetry data, short e-mail messages (send only) and storm forecasts. Once transmitted, these reports can be combined with a computer and mapping software to show the transmitted data superimposed with great precision upon a map display. While the map plotting is the most visible feature of APRS,

2755-983: Is   E I R P ( d B W ) = P T X   ( d B W ) − L ( d B ) + G ( d B i )   , {\displaystyle \ {\mathsf {EIRP}}_{\mathsf {(dB_{W})}}=P_{{\mathsf {TX}}\ {\mathsf {(dB_{W})}}}-L_{\mathsf {(dB)}}+G_{\mathsf {(dB_{i})}}\ ,}   E R P ( d B W ) = P T X   ( d B W ) − L ( d B ) + G ( d B i ) − 2.15   d B   . {\displaystyle \ {\mathsf {ERP}}_{\mathsf {(dB_{W})}}=P_{{\mathsf {TX}}\ {\mathsf {(dB_{W})}}}-L_{\mathsf {(dB)}}+G_{\mathsf {(dB_{i})}}-2.15\ {\mathsf {dB}}~.} Losses in

2850-402: Is 8.77 dB d = 10.92 dB i . Its gain necessarily must be less than this by the factor η, which must be negative in units of dB. Neither ERP nor EIRP can be calculated without knowledge of the power accepted by the antenna, i.e., it is not correct to use units of dB d or dB i with ERP and EIRP. Let us assume a 100 watt (20 dB W ) transmitter with losses of 6 dB prior to

2945-422: Is a constant, i.e., 0 dB d = 2.15 dB i . Therefore, ERP is always 2.15 dB less than EIRP. The ideal dipole antenna could be further replaced by an isotropic radiator (a purely mathematical device which cannot exist in the real world), and the receiver cannot know the difference so long as the input power is increased by 2.15 dB. The distinction between dB d and dB i is often left unstated and

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3040-538: Is also directional horizontally, gain and ERP will vary with azimuth ( compass direction). Rather than the average power over all directions, it is the apparent power in the direction of the peak of the antenna's main lobe that is quoted as a station's ERP (this statement is just another way of stating the definition of ERP). This is particularly applicable to the huge ERPs reported for shortwave broadcasting stations, which use very narrow beam widths to get their signals across continents and oceans. ERP for FM radio in

3135-598: Is fixed size and all bulletins from all posters are sorted onto this display. The intent of this display is to be consistent and identical for all viewers so that all participants are seeing the same information at the same time. Since lines are sorted onto the display, then individual posters can edit, update, or delete individual lines of their bulletins at any time to keep the bulletin board up-to-date to all viewers. All APRS messages are delivered live in real-time to online recipients. Messages are not stored and forwarded, but retried until timed out. The delivery of these messages

3230-421: Is free-field format that lets each station announce its current mission or application or contact information or any other information or data of immediate use to surrounding activities. The message packet can be used for point-to-point messages, bulletins, announcements or even email. Bulletins and Announcements are treated specially and displayed on a single "community Bulletin board". This community bulletin board

3325-404: Is global, since the APRS-IS distributes all packets to all other IGates in the world and those that are messages will actually go back to RF via any IGate that is near the intended recipient. A special case message can be sent to EMAIL where these messages are pulled off the real-time APRS-IS and wrapped into a standard email message type, and forwarded into regular Internet email. This was done by

3420-406: Is larger it will be used instead. The maximum ERP for US FM broadcasting is usually 100,000 watts (FM Zone II) or 50,000 watts (in the generally more densely populated Zones I and I-A), though exact restrictions vary depending on the class of license and the antenna height above average terrain (HAAT). Some stations have been grandfathered in or, very infrequently, been given

3515-445: Is needed. One solution to the path selection is proportional pathing if the user's equipment is capable. Early on, the widely accepted method of configuring stations was to enable the short-range stations to repeat packets requesting a path of "RELAY" and long-range stations were configured to repeat both "RELAY" and "WIDE" packets. This was accomplished by setting the station's MYALIAS setting to RELAY or WIDE as needed. This resulted in

3610-767: Is not issued to such stations due to their unlicensed nature. Also, wireless network routers or mobile devices and computers using Wi-Fi are unlicensed and do not have call signs. On some personal radio services, such as CB, it is considered a matter of etiquette to create one's own call sign, which is called a handle (or trail name). Some wireless networking protocols also allow SSIDs or MAC addresses to be set as identifiers, but with no guarantee that this label will remain unique. Many mobile telephony systems identify base transceiver stations by implementing cell ID and mobile stations (e.g., phones) by requiring them to authenticate using international mobile subscriber identity (IMSI). International regulations no longer require

3705-438: Is quantified by the antenna gain , which is the ratio of the signal strength radiated by an antenna in its direction of maximum radiation to that radiated by a standard antenna. For example, a 1,000 watt transmitter feeding an antenna with a gain of 4× (equiv. 6 dBi) will have the same signal strength in the direction of its main lobe, and thus the same ERP and EIRP, as a 4,000 watt transmitter feeding an antenna with

3800-481: Is the same as ERP, except that a short vertical antenna (i.e. a short monopole ) is used as the reference antenna instead of a half-wave dipole . Cymomotive force ( CMF ) is an alternative term used for expressing radiation intensity in volts , particularly at the lower frequencies. It is used in Australian legislation regulating AM broadcasting services, which describes it as: "for a transmitter, [it] means

3895-522: Is transported over the AX.25 protocol using 1,200-bit/s Bell 202 AFSK on frequencies located within the 2-meter amateur band . An extensive digital repeater, or "digipeater" network provides transport for APRS packets on these frequencies. Internet gateway stations (IGates) connect the on-air APRS network to the APRS Internet System (APRS-IS), which serves as a worldwide, high-bandwidth backbone for APRS data. Stations can tap into this stream directly, and

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3990-448: Is typical for medium or longwave broadcasting, skywave , or indirect paths play a part in transmission, the waves will suffer additional attenuation which depends on the terrain between the antennas, so these formulas are not valid. Because ERP is calculated as antenna gain (in a given direction) as compared with the maximum directivity of a half-wave dipole antenna , it creates a mathematically virtual effective dipole antenna oriented in

4085-683: Is used for shortwave stations; ZYC , ZYD , ZYM , and ZYU are given to FM stations. In Australia, broadcast call signs are optional, but are allocated by the Australian Communications and Media Authority and are unique for each broadcast station. Most European and Asian countries do not use call signs to identify broadcast stations, but Japan, South Korea, Indonesia, the Philippines and Taiwan do have call sign systems. Spanish broadcasters used call signs consisting of E followed by two letters and up to three digits until

4180-486: Is usually connected to the antenna through a transmission line and impedance matching network . Since these components may have significant losses   L   , {\displaystyle \ L\ ,} the power applied to the antenna is usually less than the output power of the transmitter   P T X   . {\displaystyle \ P_{\mathsf {TX}}~.} The relation of ERP and EIRP to transmitter output power

4275-544: The Dominion of Newfoundland government retain their original VO calls. In Mexico, AM radio stations use XE call signs (such as XEW-AM ), while the majority of FM radio and television stations use XH . Broadcast call signs are normally four or five alpha characters in length, plus the -FM , -TV , or -TDT suffix where applicable. In South America call signs have been a traditional way of identifying radio and TV stations. Some stations still broadcast their call signs

4370-1681: The Mississippi River and W for eastern stations. Historic exceptions in the east include KYW in Philadelphia and KDKA in Pittsburgh, while western exceptions include WJAG in Norfolk, Nebraska , and WOAI in San Antonio. All new call signs have been four-character for some decades, though there are historical three-character call letters still in use today, such as KSL in Salt Lake City; KOA in Denver; WHO in Des Moines; WWJ and WJR in Detroit; WJW-TV in Cleveland ; WBT in Charlotte; WBZ in Boston; WSM in Nashville; WGR in Buffalo; KFI ; KNX and KHJ in Los Angeles; and WGN , WLS and WLS-TV in Chicago. American radio stations announce their call signs (except for rare cases in which would interfere with

4465-518: The 1960s when flight radio officers (FRO) were no longer required on international flights. The Russian Federation kept FROs for the Moscow-Havana run until around 2000. Currently, 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

4560-551: The APRS equipment. The map display uses these fields to plot communication range of all participants and facilitate the ability to contact users during both routine and emergency situations . Each position/object/item packet can use any of several hundred different symbols. Position/objects/items can also contain weather information or can be any number of dozens of standardised weather symbols. Each symbol on an APRS map can display many attributes, discriminated either by colour or other technique. These attributes are: The Status packet

4655-1195: The EIRP or ERP. Since an isotropic antenna radiates equal power flux density over a sphere centered on the antenna, and the area of a sphere with radius   r   {\displaystyle \ r\ } is   A = 4 π   r 2   {\displaystyle \ A=4\pi \ r^{2}\ } then   S ( r ) =   E I R P     4 π   r 2     . {\displaystyle \ S(r)={\frac {\ {\mathsf {EIRP}}\ }{\ 4\pi \ r^{2}\ }}~.} Since   E I R P = E R P × 1.64   , {\displaystyle \ \mathrm {EIRP} =\mathrm {ERP} \times 1.64\ ,}   S ( r ) =   0.410 × E R P     π   r 2     . {\displaystyle \ S(r)={\frac {\ 0.410\times {\mathsf {ERP}}\ }{\ \pi \ r^{2}\ }}~.} After dividing out

4750-632: The FCC database shows the station's transmitter power output, not ERP. According to the Institution of Electrical Engineers (UK), ERP is often used as a general reference term for radiated power, but strictly speaking should only be used when the antenna is a half-wave dipole, and is used when referring to FM transmission. Effective monopole radiated power ( EMRP ) may be used in Europe, particularly in relation to medium wave broadcasting antennas. This

4845-501: The FireNet and PropNET projects. Call sign In broadcasting and radio communications , a call sign (also known as a call name or call letters —and historically as a call signal —or abbreviated as a call ) is a unique identifier for a transmitter station . A call sign can be formally assigned by a government agency, informally adopted by individuals or organizations, or even cryptographically encoded to disguise

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4940-508: The Internet to instantly obtain the address of another amateur radio operator and their QSL Managers. The most well known and used on-line QSL databases include QRZ.COM, IK3QAR, HamCall, F6CYV, DXInfo, OZ7C and QSLInfo. Effective radiated power Effective radiated power ( ERP ), synonymous with equivalent radiated power , is an IEEE standardized definition of directional radio frequency (RF) power, such as that emitted by

5035-496: The United States is always relative to a theoretical reference half-wave dipole antenna. (That is, when calculating ERP, the most direct approach is to work with antenna gain in dB d ). To deal with antenna polarization, the Federal Communications Commission (FCC) lists ERP in both the horizontal and vertical measurements for FM and TV. Horizontal is the standard for both, but if the vertical ERP

5130-464: The WU2Z email engine until 2019 , when it was replaced by the javAPRSSrvr email gateway . In its simplest implementation, APRS is used to transmit real-time data, information and reports of the exact location of a person or object via a data signal sent over amateur radio frequencies. In addition to real-time position reporting capabilities using attached GPS receivers, APRS is also capable of transmitting

5225-428: The actual total power radiated by the antenna. 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; an isotropic antenna and a half-wave dipole antenna: In contrast to an isotropic antenna, the dipole has a "donut-shaped" radiation pattern, its radiated power is maximum in directions perpendicular to

5320-754: The amateur radio service as a citizen of their country has been assigned there. The first amateur radio call sign assigned to the International Space Station was NA1SS by the United States. OR4ISS (Belgium), DP0ISS (Germany), and RS0ISS (Russia) are examples of others, but are not all-inclusive of others also issued. Broadcasters are allocated call signs in many countries. While broadcast radio stations will often brand themselves with plain-text names, identities such as " Cool FM ", " Rock 105" or "the ABC network" are not globally unique. Another station in another city or country may (and often will) have

5415-426: The antenna itself are included in the gain. If the signal path is in free space ( line-of-sight propagation with no multipath ) the signal strength ( power flux density in watts per square meter)   S   {\displaystyle \ S\ } of the radio signal on the main lobe axis at any particular distance r {\displaystyle r} from the antenna can be calculated from

5510-1002: 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 10 ⁡ ( 1.64 ) = 2.15   d B   , {\displaystyle \ 10\ \log _{10}(1.64)=2.15\ {\mathsf {dB}}\ ,} so   G i = 1.64   G d   . {\displaystyle \ G_{\mathsf {i}}=1.64\ G_{\mathsf {d}}~.} In decibels   G ( d B i ) = G ( d B d ) + 2.15   d B   . {\displaystyle \ G_{\mathsf {(dB_{i})}}=G_{\mathsf {(dB_{d})}}+2.15\ {\mathsf {dB}}~.} The two measures EIRP and ERP are based on

5605-426: The antenna. ERP < 22.77 dB W and EIRP < 24.92 dB W , both less than ideal by η in dB. Assuming that the receiver is in the first side-lobe of the transmitting antenna, and each value is further reduced by 7.2 dB, which is the decrease in directivity from the main to side-lobe of a Yagi–Uda. Therefore, anywhere along the side-lobe direction from this transmitter, a blind receiver could not tell

5700-418: The backbone of the APRS system, and use store and forward technology to retransmit packets. All stations operate on the same radio channel, and packets move through the network from digipeater to digipeater, propagating outward from their point of origin. All stations within radio range of each digipeater receive the packet. At each digipeater, the packet path is changed. The packet will be repeated through only

5795-539: The broadcast of very long works of classical or opera music) at or near the top of each hour, as well as sign-on and sign-off for stations that do not broadcast 24 hours. Beginning in the early 2000s, digital subchannels were assigned a -DT# suffix, where # is the subchannel (starting with the number 2). In Canada, the publicly owned Canadian Broadcasting Corporation uses the prefix CB ; privately owned commercial broadcast stations use primarily CF and CH through CK prefixes; and four stations licensed to St. John's by

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5890-551: The call sign corresponding to the aircraft's registration number (also called N-number in the U.S., or tail number ). In this case, the call sign is spoken using the International Civil Aviation Organization (ICAO) 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

5985-575: The case of medium wave (AM) stations in the United States , power limits are set to the actual transmitter power output, and ERP is not used in normal calculations. Omnidirectional antennas used by a number of stations radiate the signal equally in all horizontal directions. Directional arrays are used to protect co- or adjacent channel stations, usually at night, but some run directionally continuously. While antenna efficiency and ground conductivity are taken into account when designing such an array,

6080-1074: 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 (for example, 3LXY, and sometimes followed by a number, e.g. 3LXY2). 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". Originally, 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 (both radiotelegraphy and radiotelephony) were assigned three-letter call signs. As demand for both marine radio and broadcast call signs grew, gradually 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

6175-517: The country/territory identifier is, instead, appended to the call sign; e.g., W1AW/VE4, or VE3XYZ/W1. Special call signs are issued in the amateur radio service either for special purposes, VIPs, or for temporary use to commemorate special events. Examples include VO1S ( VO1 as a Dominion of Newfoundland call sign prefix, S to commemorate Marconi 's first trans-Atlantic message, a single-character Morse code S sent from Cornwall , England to Signal Hill, St. John's in 1901) and GB90MGY ( GB as

6270-515: The current American system of civilian aircraft call signs (see below). One exception to the parallelism between registration and call sign is ultralight airplanes in France, who are not obliged to carry a radio and indeed often don't. Radio call signs used for communication in crewed spaceflight are not formalized or regulated to the same degree as for aircraft. The three nations currently launching crewed space missions use different methods to identify

6365-743: The designated call sign, so F13C would be the Charlie fire team . Unused suffixes can be used for other call signs that do not fall into the standard call sign matrix, for example the unused 33A call sign is used to refer to the company sergeant major . No call signs are issued to transmitters of the long-range navigation systems ( Decca , Alpha , Omega ), or transmitters on frequencies below 10 kHz , because frequencies below 10 kHz are not subject to international regulations. In addition, in some countries lawful unlicensed low-power personal and broadcast radio signals ( Citizen's Band (CB), Part 15 or ISM bands ) are permitted; an international call sign

6460-403: The difference if a Yagi–Uda was replaced with either an ideal dipole (oriented towards the receiver) or an isotropic radiator with antenna input power increased by 1.57 dB. Polarization has not been taken into account so far, but it must be properly clarified. When considering the dipole radiator previously we assumed that it was perfectly aligned with the receiver. Now assume, however, that

6555-476: The direction of the receiver. In other words, a notional receiver in a given direction from the transmitter would receive the same power if the source were replaced with an ideal dipole oriented with maximum directivity and matched polarization towards the receiver and with an antenna input power equal to the ERP. The receiver would not be able to determine a difference. Maximum directivity of an ideal half-wave dipole

6650-434: The factor of   π   , {\displaystyle \ \pi \ ,} we get:   S ( r ) =   0.131 × E R P     r 2     . {\displaystyle \ S(r)={\frac {\ 0.131\times {\mathsf {ERP}}\ }{\ r^{2}\ }}~.} However, if the radio waves travel by ground wave as

6745-563: 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 . Originally aviation mobile stations (aircraft) equipped with radiotelegraphy were assigned five-letter call signs (e.g. KHAAQ). Land stations in aviation were assigned four-letter call signs (e.g. WEAL – Eastern Air Lines, NYC.) These call signs were phased out in

6840-434: The ground and space radio stations; the United States uses either the names given to the space vehicles, or else the project name and mission number. Russia traditionally assigns code names as call signs to individual cosmonauts , more in the manner of aviator call signs , rather than to the spacecraft. The only continuity in call signs for spacecraft have been the issuance of "ISS"-suffixed call signs by various countries in

6935-509: The international series. The United States Army uses fixed station call signs which begin with W , such as WAR, used by U.S. Army Headquarters. Fixed call signs for the United States Air Force stations begin with A , such as AIR, used by USAF Headquarters. The United States Navy , United States Marine Corps , and United States Coast Guard use a mixture of tactical call signs and international call signs beginning with

7030-465: The jurisdiction of a foreign government, an identifying station pre-pends the call sign with the country prefix and number of the country/territory from which the operation is occurring. For example, W4/G3ABC would denote a licensed amateur from the United Kingdom who is operating in the fourth district of the United States. There are exceptions; in the case of U.S./Canadian reciprocal operations,

7125-483: The late 1970s. Portugal had a similar system, their callsigns beginning with C ; these also ceased to be used in the 1970s. Britain has no call signs in the American sense, but allows broadcast stations to choose their own trade mark call sign up to six words in length. Amateur radio call signs are in the international series and normally consist of a one or two character prefix, a digit (which may be used to denote

7220-415: The latitude and longitude, and a symbol to be displayed on the map, and have many optional fields for altitude, course, speed, radiated power , antenna height above average terrain , antenna gain , and voice operating frequency. Positions of fixed stations are configured in the APRS software. Moving stations (portable or mobile) automatically derive their position information from a GPS receiver connected to

7315-464: The letter N . In the British military , tactical voice communications use a system of call signs of the form letter-digit-digit . Within a standard infantry battalion, these characters represent companies, platoons and sections respectively, so that 3 Section, 1 Platoon of F Company might be F13. In addition, a suffix following the initial call sign can denote a specific individual or grouping within

7410-430: The name and addressees of licensed radio stations in a given jurisdiction (country). Modern Electrics published the first callbook in the United States in 1909. Today, the primary purpose of a callbook is to allow amateur radio operators to send a confirmation post card, called a QSL card to an operator with whom they have communicated via radio. Callbooks have evolved to include on-line databases that are accessible via

7505-484: 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 one or two letters followed by three or four numbers (such as KX0983 or WXX0029). U.S. Coast Guard small boats have a number that is shown on both bows (i.e. port and starboard) in which

7600-539: The originating station. Packets can be digitally repeated tens of kilometers or even hundreds of kilometers, depending on the height and range of the digipeaters in the area. When a packet is transmitted, it is duplicated many times as it radiates out, taking all available paths simultaneously, until the number of "hops" allowed by the path setting is consumed. APRS contains a number of packet types, including position/object/item, status, messages, queries, weather reports and telemetry. The position/object/item packets contain

7695-451: The packet to be repeated through the two stations before it stops. In APRS, generic call signs are assigned to repeater stations to allow a more automatic operation. Throughout North America (and in many other regions) the recommended path for mobiles or portable stations is now WIDE1-1,WIDE2-1. Fixed Stations (homes, etc.) should not normally use a path routing if they do not need to be digitally repeated outside of their local area, otherwise

7790-488: The packets are routed on to the Internet APRS backbone (where duplicate packets heard by other IGates are discarded) for display or analysis by other users connected to an APRS-IS server, or on a Web site designed for the purpose. While it would seem that using unconnected and unnumbered packets without acknowledgment and retransmission on a shared and sometimes congested channel would result in poor reliability due to

7885-428: The power density a radio transmitter and antenna (or other source of electromagnetic waves) radiate in a specific direction: in the direction of maximum signal strength (the " main lobe ") of its radiation pattern. This apparent 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 direction of maximal intensity. The latter factor

7980-400: The prefix is normally a single number (0 to 9). Some prefixes, such as Djibouti's (J2), consist of a letter followed by a number. Hence, in the hypothetical Djibouti call sign, J29DBA, the prefix is J2 , the number is 9 , and the suffix is DBA . Others may start with a number followed by a letter, for example, Jamaican call signs begin with 6Y. When operating with reciprocal agreements under

8075-441: The product, expressed in volts, of: It relates to AM broadcasting only, and expresses the field strength in " microvolts per metre at a distance of 1 kilometre from the transmitting antenna". The height above average terrain for VHF and higher frequencies is extremely important when considering ERP, as the signal coverage ( broadcast range ) produced by a given ERP dramatically increases with antenna height. Because of this, it

8170-449: The reader is sometimes forced to infer which was used. For example, a Yagi–Uda antenna is constructed from several dipoles arranged at precise intervals to create greater energy focusing (directivity) than a simple dipole. Since it is constructed from dipoles, often its antenna gain is expressed in dB d , but listed only as dB. This ambiguity is undesirable with respect to engineering specifications. A Yagi–Uda antenna's maximum directivity

8265-464: The receiving antenna is circularly polarized, and there will be a minimum 3 dB polarization loss regardless of antenna orientation. If the receiver is also a dipole, it is possible to align it orthogonally to the transmitter such that theoretically zero energy is received. However, this polarization loss is not accounted for in the calculation of ERP or EIRP. Rather, the receiving system designer must account for this loss as appropriate. For example,

8360-442: The same thing is effective isotropic radiated power ( EIRP ). Effective isotropic radiated power is the hypothetical power that would have to be radiated by an isotropic antenna to give the same ("equivalent") signal strength as the actual source antenna 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

8455-591: The system was ported to the IBM Personal Computer . During the early 1990s, CETS (then known as the Automatic Position Reporting System) continued to evolve into its current form. As GPS technology became more widely available, "Position" was replaced with "Packet" to better describe the more generic capabilities of the system and to emphasize its uses beyond mere position reporting. Bruninga has also stated that APRS

8550-471: The text messaging capabilities and local information distribution capabilities, combined with the robust network, should not be overlooked; the New Jersey Office of Emergency Management has an extensive network of APRS stations to allow text messaging between all of the county Emergency Operating Centers in the event of the failure of conventional communications. In its most widely used form, APRS

8645-513: The tower controller. For example, Skyhawk eight-Charlie-Papa, left base . In commercial aviation, the callsign is usually the ICAO Flight number . For example, Delta Airlines Flight 744 would have the flight number DL744 and the callsign would be Delta 744 . In most countries, the aircraft call sign or "tail number"/"tail letters" (also known as registration marks) are linked to the international radio call sign allocation table and follow

8740-407: 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 , particularly in broadcasting to quantify the apparent power of a broadcasting station experienced by listeners in its reception area. An alternate parameter that measures

8835-789: The two different standard antennas above: Since the two definitions of gain only differ by a constant factor, so do ERP and EIRP   E I R P ( W ) = 1.64 × E R P ( W )   . {\displaystyle \ {\mathsf {EIRP}}_{\mathsf {(W)}}=1.64\times {\mathsf {ERP}}_{\mathsf {(W)}}~.} In decibels   E I R P ( d B W ) = E R P ( d B W ) + 2.15   d B   . {\displaystyle \ {\mathsf {EIRP}}_{\mathsf {(dB_{W})}}={\mathsf {ERP}}_{\mathsf {(dB_{W})}}+2.15\ {\mathsf {dB}}~.} The transmitter

8930-761: Was not meant to be a vehicle position tracking system, and can be interpreted rather as "Automatic Presence Reporting System". APRS (Automatic Packet Reporting System), is a digital communications protocol for exchanging information among a large number of stations covering a large (local) area, often referred to as " IP -ers". As a multi-user data network, it is quite different from conventional packet radio . Rather than using connected data streams where stations connect to each other and packets are acknowledged and retransmitted if lost, APRS operates entirely in an unconnected broadcast fashion, using unnumbered AX.25 frames. APRS packets are transmitted for all other stations to hear and use. Packet repeaters , called digipeaters, form

9025-573: Was used to map high frequency Navy position reports. The first use of APRS was in 1984, when Bruninga developed a more advanced version on a VIC-20 for reporting the position and status of horses in a 100-mile (160 km) endurance run. During the next two years, Bruninga continued to develop the system, which he then called the Connectionless Emergency Traffic System (CETS). Following a series of Federal Emergency Management Agency (FEMA) exercises using CETS,

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