In electronics and telecommunications, a transmitter or radio transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, 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 and television broadcasting stations, cell phones, walkie-talkies, wireless computer networks, Bluetooth enabled devices, garage door openers, two-way radios in aircraft, spacecraft, radar sets and navigational beacons; the term transmitter is limited to equipment that generates radio waves for communication purposes. Generators of radio waves for heating or industrial purposes, such as microwave ovens or diathermy equipment, are not called transmitters though they have similar circuits; the term is popularly used more to refer to a broadcast transmitter, a transmitter used in broadcasting, as in FM radio transmitter or television transmitter.
This usage includes both the transmitter proper, the antenna, 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 is called a transceiver; the term transmitter is abbreviated "XMTR" or "TX" in technical documents. 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, such as an audio signal from a microphone, a video signal from a video camera, or in wireless networking devices, a digital signal from a computer. The transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, called the carrier signal; this process is called modulation. The information can be added to the carrier in several different ways, in different types of transmitters. In an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude.
In a frequency modulation transmitter, it is added by varying the radio signal's frequency slightly. Many other types of modulation are 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, garage door openers. In more powerful transmitters, the antenna may be located on top of a building or on a separate tower, connected to the transmitter by a feed line, a transmission line. Electromagnetic waves are radiated by electric charges undergoing acceleration. 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 or direction and thus accelerating. An alternating current flowing back and forth in an antenna will create an oscillating magnetic field around the conductor.
The alternating voltage will 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, a radio wave. A radio transmitter is an electronic circuit which transforms electric power from a power source into a radio frequency alternating current to apply to the antenna, the antenna radiates the energy from this current as radio waves; the transmitter impresses information such as an audio or video signal onto the radio frequency current to be carried by the radio waves. When they strike the antenna of a radio receiver, the waves excite similar radio frequency currents in it; the radio receiver extracts the information from the received waves. A practical radio transmitter consists of these parts: A power supply circuit to transform the input electrical power to the higher voltages needed to produce the required power output.
An electronic oscillator circuit to generate the radio frequency signal. This generates a sine wave of constant amplitude called the carrier wave, because it serves to "carry" the information through space. In most modern transmitters, this is a crystal oscillator in which the frequency is controlled by the vibrations of a quartz crystal; the frequency of the carrier wave is considered the frequency of the transmitter. A modulator circuit to add the information to be transmitted to the carrier wave produced by the oscillator; this is done by varying some aspect of the carrier wave. The information is provided to the transmitter either in the form of an audio signal, which represents sound, a video signal which represents moving images, or for data in the form of a binary digital signal which represents a sequence of bits, a bitstream. Different types of transmitters use different modulation methods to transmit information: In an AM transmitter the amplitude of the carrier wave is varied in proportion to the modulation signal.
In an FM transmitter the frequency of the carrier is varied by the modulation signal. In an FSK transmitter, which transmits digital data, the frequency of the carrier is shifted between two frequencies which represent the two binary digits, 0 and 1. Many oth
Telecommunication is the transmission of signs, messages, writings and sounds or information of any nature by wire, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology, it is transmitted either electrically over physical media, such as cables, or via electromagnetic radiation. Such transmission paths are divided into communication channels which afford the advantages of multiplexing. Since the Latin term communicatio is considered the social process of information exchange, the term telecommunications is used in its plural form because it involves many different technologies. Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, optical heliographs. Other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, loud whistles. 20th- and 21st-century technologies for long-distance communication involve electrical and electromagnetic technologies, such as telegraph and teleprinter, radio, microwave transmission, fiber optics, communications satellites.
A revolution in wireless communication began in the first decade of the 20th century with the pioneering developments in radio communications by Guglielmo Marconi, who won the Nobel Prize in Physics in 1909, other notable pioneering inventors and developers in the field of electrical and electronic telecommunications. These included Charles Wheatstone and Samuel Morse, Alexander Graham Bell, Edwin Armstrong and Lee de Forest, as well as Vladimir K. Zworykin, John Logie Baird and Philo Farnsworth; the word telecommunication is a compound of the Greek prefix tele, meaning distant, far off, or afar, the Latin communicare, meaning to share. Its modern use is adapted from the French, because its written use was recorded in 1904 by the French engineer and novelist Édouard Estaunié. Communication was first used as an English word in the late 14th century, it comes from Old French comunicacion, from Latin communicationem, noun of action from past participle stem of communicare "to share, divide out.
Homing pigeons have been used throughout history by different cultures. Pigeon post had Persian roots, was used by the Romans to aid their military. Frontinus said; the Greeks conveyed the names of the victors at the Olympic Games to various cities using homing pigeons. In the early 19th century, the Dutch government used the system in Sumatra, and in 1849, Paul Julius Reuter started a pigeon service to fly stock prices between Aachen and Brussels, a service that operated for a year until the gap in the telegraph link was closed. In the Middle Ages, chains of beacons were used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could only pass a single bit of information, so the meaning of the message such as "the enemy has been sighted" had to be agreed upon in advance. One notable instance of their use was during the Spanish Armada, when a beacon chain relayed a signal from Plymouth to London. In 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system between Lille and Paris.
However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres. As a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880. On 25 July 1837 the first commercial electrical telegraph was demonstrated by English inventor Sir William Fothergill Cooke, English scientist Sir Charles Wheatstone. Both inventors viewed their device as "an improvement to the electromagnetic telegraph" not as a new device. Samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837, his code was an important advance over Wheatstone's signaling method. The first transatlantic telegraph cable was completed on 27 July 1866, allowing transatlantic telecommunication for the first time; the conventional telephone was invented independently by Alexander Bell and Elisha Gray in 1876. Antonio Meucci invented the first device that allowed the electrical transmission of voice over a line in 1849.
However Meucci's device was of little practical value because it relied upon the electrophonic effect and thus required users to place the receiver in their mouth to "hear" what was being said. The first commercial telephone services were set-up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London. Starting in 1894, Italian inventor Guglielmo Marconi began developing a wireless communication using the newly discovered phenomenon of radio waves, showing by 1901 that they could be transmitted across the Atlantic Ocean; this was the start of wireless telegraphy by radio. Voice and music had little early success. World War I accelerated the development of radio for military communications. After the war, commercial radio AM broadcasting began in the 1920s and became an important mass medium for entertainment and news. World War II again accelerated development of radio for the wartime purposes of aircraft and land communication, radio navigation and radar. Development of stereo FM broadcasting of radio
Ground control station
For satellite ground stations, see Ground station. A ground control station is a land- or sea-based control centre that provides the facilities for human control of Unmanned Aerial Vehicles, it may refer to a system for controlling rockets within or above the atmosphere, but this is discussed elsewhere. GCS hardware refers to the complete set of ground-based hardware systems used to control the UAV; this includes the Human-Machine Interface, telemetry, video capture card and aerials for the control and data links to the UAV. Larger military UAVs such as the General Atomics MQ-1 Predator feature what resembles a "virtual cockpit"; the pilot or sensor operator sits in front of a number of screens showing the view from the UAV, a map screen and aircraft instrumentation. Control is through a conventional aircraft-style joystick and throttle with Hands on Throttle and Stick functionality. In addition, the GCS consists of satellite or long-range communication links that are mounted on the roof or on a separate vehicle, container or building.
Smaller UAVs can be operated with a traditional "twin-stick" style transmitter, as used for radio controlled model aircraft. Extending this setup with a laptop or tablet computer and video telemetry, aerials, creates what is a Ground Control Station. A number of suppliers offer a combined system that consists of what looks like a modified transmitter combined with what is a touch screen. An internal computer running the GCS software sits behind the screen, along with the video and data links. Larger GCS units are available that fit inside flight cases; as with the smaller units, they feature an internal computer running the GCS software, along with video and data links. Large single or dual screens are fitted that can be high-brightness or treated with an anti-glare coating to increase visibility in bright sunlight, they can either feature integrated folding legs. Some portable GCS units are in the HOTAS layout; this layout includes a 3-Axis Joystick to control yaw and roll of the UAV. A slide or t-bar fader can increase or decrease the airspeed of the UAV.
GCS software is runs on a ground-based computer, used for planning and flying a mission. It provides a map screen where the user can define waypoints for the flight, see the progress of the mission, it serves as a “virtual cockpit”, showing many of the same instruments as in manned aircraft. Unmanned aerial vehicle Shadow 200 TUAV Mission control center Rocket launch Unmanned aircraft system
Flight plans are documents filed by a pilot or flight dispatcher with the local Civil Aviation Authority prior to departure which indicate the plane's planned route or flight path. Flight plan format is specified in ICAO Doc 4444, they include basic information such as departure and arrival points, estimated time en route, alternate airports in case of bad weather, type of flight, the pilot's information, number of people on board and information about the aircraft itself. In most countries, flight plans are required for flights under IFR, but may be optional for flying VFR unless crossing international borders. Flight plans are recommended when flying over inhospitable areas, such as water, as they provide a way of alerting rescuers if the flight is overdue. In the United States and Canada, when an aircraft is crossing the Air Defense Identification Zone, either an IFR or a special type of VFR flight plan called a DVFR flight plan must be filed. For IFR flights, flight plans are used by air traffic control to initiate tracking and routing services.
For VFR flights, their only purpose is to provide needed information should search and rescue operations be required, or for use by air traffic control when flying in a "Special Flight Rules Area". Routing types used in flight planning are: airway and direct. A route may be composed of segments of different routing types. For example, a route from Chicago to Rome may include airway routing over the U. S. and Europe, but direct routing over the Atlantic Ocean. Airway routing occurs along pre-defined pathways called flight paths. Airways can be thought of as three-dimensional highways for aircraft. In most land areas of the world, aircraft are required to fly airways between the departure and destination airports; the rules governing airway routing cover altitude and requirements for entering and leaving the airway. Most airways are eight nautical miles wide, the airway flight levels keep aircraft separated by at least 1000 vertical feet from aircraft on the flight level above and below. Airways intersect at Navaids, which designate the allowed points for changing from one airway to another.
Airways have names consisting of one or more letters followed by one or more digits. The airway structure is divided into low altitudes; the low altitude airways in the U. S. which can be navigated using VOR Navaids have names that start with the letter V, are therefore called Victor Airways. They cover altitudes from 1200 feet above ground level to 17,999 feet above mean sea level. T routes are low altitude RNAV only routes which may or may not utilize VOR NAVAIDS; the high altitude airways in the U. S. have names that are called Jet Routes, or Q for Q routes. Q routes in the U. S. are RNAV only high altitude airways. J & Q routes run from 18,000 feet to 45,000 feet; the altitude separating the low and high airway structures varies from country to country. For example, it is 19,500 feet in Switzerland, 25,500 feet in Egypt. Navaid routing occurs between Navaids. Navaid routing is only allowed in the continental U. S. If a flight plan specifies Navaid routing between two Navaids which are connected via an airway, the rules for that particular airway must be followed as if the aircraft was flying Airway routing between those two Navaids.
Allowable altitudes are covered in Flight Levels. Direct routing occurs when one or both of the route segment endpoints are at a latitude/longitude, not located at a Navaid; some flight planning organizations specify that checkpoints generated for a Direct route be a limited distance apart, or limited by time to fly between the checkpoints. SIDs and STARs are procedures and checkpoints used to enter and leave the airway system by aircraft operating on IFR flight plans. There is a defined transition point at which a SID or STAR intersect. A SID, or Standard Instrument Departure, defines a pathway out of an airport and onto the airway structure. A SID is sometimes called a Departure Procedure. SIDs are unique to the associated airport. A STAR, or Standard Terminal Arrival Route, defines a pathway into an airport from the airway structure. STARs can be associated with more than one arrival airport, which can occur when two or more airports are in proximity. In general, flight planners are expected to avoid areas called Special Use Airspace when planning a flight.
In the United States, there are several types of SUA, including Restricted, Prohibited and Military Operations Area. Examples of Special Use Airspace include a region around the White House in Washington, D. C. and the country of Cuba. Government and military aircraft may have different requirements for particular SUA areas, or may be able to acquire special clearances to traverse through these areas. Flight levels are used by air traffic controllers to simplify the vertical separation of aircraft and one exists every 1000 feet relative to an agreed pressure level. Above a transitional altitude, which varies from country to country, the worldwide arbitrary pressure datum of 1013.25 millibar or the equivalent setting of 29.92 inches of mercury is entered into the altimeter and altitude is referred to as a flight level. The altimeter read
A communications receiver is a type of radio receiver used as a component of a radio communication link. This is in contrast to a broadcast receiver, used to receive radio broadcasts. A communication receiver receives parts of the radio spectrum not used for broadcasting, that includes amateur, aircraft and other bands, they are used with a radio transmitter as part of a two way radio link for shortwave radio or amateur radio communication, although they are used for shortwave listening. Commercial communications receivers are characterized by high stability and reliability of performance, are adapted for remote control and monitoring. For marketing purposes, many hobby-type receivers are advertised as "communications receivers" although none are suited for heavy-duty, reliable 24-hour use as the primary form of communication for an isolated station. A communications receiver is of the superheterodyne type in double, triple or, more quad conversion, it features multiple RF and IF amplification stages and may have at least one IF stage, crystal controlled.
It has a BFO and a product detector for SSB and CW reception. The frequency coverage of receivers of this type is in the range of 500 kHz to 30 MHz. Communication receivers are suited for operation near powerful transmitting facilities and so must have good internal shielding, effective front-end filtering, they have design features to provide high stability. Rejection of unwanted signals will be much greater than a consumer-type general coverage or broadcast receiver; the front panel controls are more comprehensive than those on a broadcasting receiver. Usual features include: signal strength meter. Precise, analog tuning and display dials are used, with a separate bandspread control to allow selective tuning of signals close in frequency. In more recent units, electronic digital frequency displays are provided. In communication receivers, the decorative wooden cabinets typical of early broadcast receivers were replaced with utilitarian metal cabinets to provide electromagnetic shielding and mechanical ruggedness.
Communications receivers as an identifiable product type originated in 1933. The older generation of tube-based communications receivers are affectionately known as boatanchors for their large size and weight; such receivers include the Collins R-390 and R-390A, the RCA AR-88, the Racal RA-17L and the Marconi Electra. However modern solid-state receivers can be large and heavy, such as the Plessey PR2250, the Redifon R551 or the Rohde & Schwarz EK070/D2-80. Amateur radio Scanner Shortwave radio receiver Shortwave listening Shortwave radio Wadley Loop