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37-661: Radio beacons transmit a continuous or periodic radio signal with limited information (for example, its identification or location) on a specified radio frequency . Occasionally, the beacon's transmission includes other information, such as telemetric or meteorological data. Radio beacons have many applications, including air and sea navigation, propagation research, robotic mapping , radio-frequency identification (RFID), near-field communication (NFC) and indoor navigation , as with real-time locating systems (RTLS) like Syledis or simultaneous localization and mapping (SLAM). The most basic radio-navigational aid used in aviation

74-457: A broadcast transmitter , a transmitter used in broadcasting , as in FM radio transmitter or television transmitter . This usage typically includes both the transmitter proper, the antenna, and often the building it is housed in. A transmitter can be a separate piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit

111-472: A frequency modulation (FM) transmitter, it is added by varying the radio signal's frequency slightly. Many other types of modulation are also used. The radio signal from the transmitter is applied to the antenna , which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as cell phones, walkie-talkies, and garage door openers . In more powerful transmitters,

148-429: A radio frequency signal which when applied to the antenna produces the radio waves, called the carrier signal . It combines the carrier with the modulation signal, a process called modulation . The information can be added to the carrier in several different ways, in different types of transmitters. In an amplitude modulation (AM) transmitter, the information is added to the radio signal by varying its amplitude . In

185-597: A radio receiver . The transmitter itself generates a radio frequency alternating current , which is applied to the antenna . When excited by this alternating current, the antenna radiates radio waves. Transmitters are necessary component parts of all electronic devices that communicate by radio , such as radio (audio) and television broadcasting stations, cell phones , walkie-talkies , wireless computer networks , Bluetooth enabled devices, garage door openers , two-way radios in aircraft, ships, spacecraft, radar sets and navigational beacons. The term transmitter

222-435: A single-frequency network should not be used as in this case the direction of the minimum or the maximum can be different from the direction to the transmitter site. A marker beacon is a specialized beacon used in aviation, in conjunction with an instrument landing system (ILS), to give pilots a means to determine distance to the runway. Marker beacons transmit on the dedicated frequency of 75 MHz. This type of beacon

259-549: A fixed frequency) whose purpose is twofold; as well as containing modulated station-keeping information (telemetry), the beacon locates the satellite (determines its azimuth and elevation) in the sky. A beacon was left on the Moon by crew of Apollo 17 , the last Apollo mission, transmitting FSK telemetry on 2276.0 MHz Driftnet radio buoys are extensively used by fishing boats operating in open seas and oceans. They are useful for collecting long fishing lines or fishing nets, with

296-466: A formal machine-readable beacon text specification developed by Bob Bruninga, WB4APR, became the basis of the APRS networks. Transmitter In electronics and telecommunications , a radio transmitter or just transmitter (often abbreviated as XMTR or TX in technical documents) is an electronic device which produces radio waves with an antenna with the purpose of signal transmission up to

333-518: A high voltage spark between two conductors. Beginning in 1895, Guglielmo Marconi developed the first practical radio communication systems using these transmitters, and radio began to be used commercially around 1900. Spark transmitters could not transmit audio (sound) and instead transmitted information by radiotelegraphy : the operator tapped on a telegraph key which turned the transmitter on-and-off to produce radio wave pulses spelling out text messages in telegraphic code, usually Morse code . At

370-413: A radio wave. A radio transmitter is an electronic circuit which transforms electric power from a power source, a battery or mains power, into a radio frequency alternating current to apply to the antenna, and the antenna radiates the energy from this current as radio waves. The transmitter also encodes information such as an audio or video signal into the radio frequency current to be carried by

407-571: A variety of license classes depending on use such as broadcast , marine radio , Airband , Amateur and are restricted to certain frequencies and power levels. A body called the International Telecommunication Union (ITU) allocates the frequency bands in the radio spectrum to various classes of users. In some classes, each transmitter is given a unique call sign consisting of a string of letters and numbers which must be used as an identifier in transmissions. The operator of

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444-425: Is called a transceiver . The purpose of most transmitters is radio communication of information over a distance. The information is provided to the transmitter in the form of an electronic signal called the modulation signal, such as an audio (sound) signal from a microphone, a video (TV) signal from a video camera, or in wireless networking devices, a digital signal from a computer. The transmitter generates

481-411: Is it can often transmit more information ( data rate ) in a given bandwidth than analog, using data compression algorithms. Other advantages of digital transmission are increased noise immunity , and greater flexibility and processing power of digital signal processing integrated circuits . Tracking transmitter A tracking transmitter broadcasts a radio signal which can be detected by

518-406: Is no official information available about these transmitters, and they are not registered with the International Telecommunication Union . Some investigators suggest that some of these so-called "cluster beacons" are actually radio propagation beacons for naval use. Beacons are also used in both geostationary and inclined-orbit satellites. Any satellite will emit one or more beacons (normally on

555-478: Is slowly being phased out, and most new ILS installations have no marker beacons. An amateur radio propagation beacon is specifically used to study the propagation of radio signals. Nearly all of them are part of the amateur radio service. A group of radio beacons with single-letter identifiers ("C", "D", "M", "S", "P", etc.) transmitting in Morse code have been regularly reported on various high frequencies . There

592-621: Is the non-directional beacon or NDB. It is a simple low- and medium-frequency transmitter used to locate airway intersections and airports and to conduct instrument approaches , with the use of a radio direction finder located on the aircraft. The aviation NDBs, especially the ones marking airway intersections, are gradually being decommissioned and replaced with other navigational aids based on newer technologies. Due to relatively low purchase, maintenance and calibration cost, NDBs are still used to mark locations of smaller aerodromes and important helicopter landing sites. Marine beacons, based on

629-411: Is usually limited to equipment that generates radio waves for communication purposes; or radiolocation , such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as microwave ovens or diathermy equipment, are not usually called transmitters, even though they often have similar circuits. The term is popularly used more specifically to refer to

666-500: The AX.25 link layer protocol also use beacon transmissions to identify themselves and broadcast brief information about operational status. The beacon transmissions use special UI or Unnumbered Information frames, which are not part of a connection and can be displayed by any station. Beacons in traditional AX.25 amateur packet radio networks contain free format information text, readable by human operators. This mode of AX.25 operation, using

703-637: The UHF and microwave ranges, using new active devices such as the magnetron , klystron , and traveling wave tube . The invention of the transistor allowed the development in the 1960s of small portable transmitters such as wireless microphones , garage door openers and walkie-talkies . The development of the integrated circuit (IC) in the 1970s made possible the current proliferation of wireless devices , such as cell phones and Wi-Fi networks, in which integrated digital transmitters and receivers ( wireless modems ) in portable devices operate automatically, in

740-676: The 1920s. All these early technologies were replaced by vacuum tube transmitters in the 1920s, which used the feedback oscillator invented by Edwin Armstrong and Alexander Meissner around 1912, based on the Audion ( triode ) vacuum tube invented by Lee De Forest in 1906. Vacuum tube transmitters were inexpensive and produced continuous waves , and could be easily modulated to transmit audio (sound) using amplitude modulation (AM). This made AM radio broadcasting possible, which began in about 1920. Practical frequency modulation (FM) transmission

777-547: The US, these fall under Part 15 of the Federal Communications Commission (FCC) regulations. Although they can be operated without a license, these devices still generally must be type-approved before sale. The first primitive radio transmitters (called spark gap transmitters ) were built by German physicist Heinrich Hertz in 1887 during his pioneering investigations of radio waves. These generated radio waves by

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814-610: The antenna may be located on top of a building or on a separate tower, and connected to the transmitter by a feed line , that is a transmission line . Electromagnetic waves are radiated by electric charges when they are accelerated . Radio waves , electromagnetic waves of radio frequency , are generated by time-varying electric currents , consisting of electrons flowing through a metal conductor called an antenna which are changing their velocity and thus accelerating. An alternating current flowing back and forth in an antenna will create an oscillating magnetic field around

851-414: The assistance of a radio direction finder . According to product information released by manufacturer Kato Electronics Co, Ltd., these buoys transmit on 1600–2850 kHz with a power of 4-15 W. Some types of driftnet buoys, called "SelCall buoys", answer only when they are called by their own ships. Using this technique the buoy prevents nets and fishing gears from being carried away by other ships, while

888-461: The background, to exchange data with wireless networks . The need to conserve bandwidth in the increasingly congested radio spectrum is driving the development of new types of transmitters such as spread spectrum , trunked radio systems and cognitive radio . A related trend has been an ongoing transition from analog to digital radio transmission methods. Digital modulation can have greater spectral efficiency than analog modulation ; that

925-441: The battery power consumption remains low. Distress radio beacons, also collectively known as distress beacons , emergency beacons , or simply beacons , are those tracking transmitters that operate as part of the international Cospas-Sarsat Search and Rescue satellite system. When activated, these beacons send out a distress signal that, when detected by non- geostationary satellites, can be located by triangulation . In

962-400: The case of 406 MHz beacons, which transmit digital signals, the beacons can be uniquely identified almost instantly (via GEOSAR ), and a GPS position can be encoded into the signal (thus providing both instantaneous identification and position). Distress signals from the beacons are homed by search and rescue (SAR) aircraft and ground search parties, who can in turn come to the aid of

999-446: The concerned boat, aircraft or persons. There are three kinds of distress radio beacons: The basic purpose of distress radio beacons is to rescue people within the so-called "golden day" (the first 24 hours following a traumatic event), when the majority of survivors can still be saved. In the field of Wi-Fi (wireless local area networks using the IEEE 802.11b and 802.11g specification),

1036-419: The conductor. The alternating voltage will also charge the ends of the conductor alternately positive and negative, creating an oscillating electric field around the conductor. If the frequency of the oscillations is high enough, in the radio frequency range above about 20 kHz, the oscillating coupled electric and magnetic fields will radiate away from the antenna into space as an electromagnetic wave,

1073-421: The output frequency. Older designs used an oscillator at a lower frequency, which was multiplied by frequency multipliers to get a signal at the desired frequency. Modern designs more commonly use an oscillator at the operating frequency which is stabilized by phase locking to a very stable lower frequency reference, usually a crystal oscillator. Two radio transmitters in the same area that attempt to transmit on

1110-400: The radio waves. When they strike the antenna of a radio receiver , the waves excite similar (but less powerful) radio frequency currents in it. The radio receiver extracts the information from the received waves. A practical radio transmitter mainly consists of the following parts: In higher frequency transmitters, in the UHF and microwave range, free running oscillators are unstable at

1147-486: The receiver, these pulses were sometimes directly recorded on paper tapes, but more common was audible reception. The pulses were audible as beeps in the receiver's earphones, which were translated back to text by an operator who knew Morse code. These spark-gap transmitters were used during the first three decades of radio (1887–1917), called the wireless telegraphy or "spark" era. Because they generated damped waves , spark transmitters were electrically "noisy". Their energy

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1184-475: The same frequency will interfere with each other, causing garbled reception, so neither transmission may be received clearly. Interference with radio transmissions can not only have a large economic cost, it can be life-threatening (for example, in the case of interference with emergency communications or air traffic control ). For this reason, in most countries, use of transmitters is strictly controlled by law. Transmitters must be licensed by governments, under

1221-490: The same technology and installed in coastal areas, have also been used by ships at sea. Most of them, especially in the Western world, are no longer in service, while some have been converted to telemetry transmitters for differential GPS . Other than dedicated radio beacons, any AM , VHF , or UHF radio station at a known location can be used as a beacon with direction-finding equipment. However stations, which are part of

1258-475: The term beacon signifies a specific data transmission from the wireless access point (AP), which carries the SSID , the channel number and security protocols such as Wired Equivalent Privacy (WEP) or Wi-Fi Protected Access (WPA). This transmission does not contain the link layer address of another Wi-Fi device, therefore it can be received by any LAN client. Stations participating in packet radio networks based on

1295-512: The transmitter usually must hold a government license, such as a general radiotelephone operator license , which is obtained by passing a test demonstrating adequate technical and legal knowledge of safe radio operation. Exceptions to the above regulations allow the unlicensed use of low-power short-range transmitters in consumer products such as cell phones , cordless telephones , wireless microphones , walkie-talkies , Wi-Fi and Bluetooth devices, garage door openers , and baby monitors . In

1332-440: Was invented by Edwin Armstrong in 1933, who showed that it was less vulnerable to noise and static than AM. The first FM radio station was licensed in 1937. Experimental television transmission had been conducted by radio stations since the late 1920s, but practical television broadcasting didn't begin until the late 1930s. The development of radar during World War II motivated the evolution of high frequency transmitters in

1369-492: Was spread over a broad band of frequencies , creating radio noise which interfered with other transmitters. Damped wave emissions were banned by international law in 1934. Two short-lived competing transmitter technologies came into use after the turn of the century, which were the first continuous wave transmitters: the arc converter ( Poulsen arc ) in 1904 and the Alexanderson alternator around 1910, which were used into

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