Transmitter
A transmitter (short transmitter) is a facility for the generation and radiation of electromagnetic waves that are modulated, for example, with language or music. It consists today mostly of an oscillator with subsequent amplifier and a transmit antenna. In addition, is also always a means for modulating the vibration necessary, so that messages can be transmitted.
In the strict sense, a device is a mobile phone, which includes these necessary components, referred to as a transmitter.
- 2.1 Protection circuits
- 2.2 building
- 3.1 Planning
High-frequency generator
History
In the early days of radio technology transmitters were built, in which the vibration generation with arcs or machines is done (eg VLF transmitter Grimeton ). But already in the 1920s continued in this area, the electronics with vacuum tubes through 1960 with semiconductor devices.
Construction and components
In principle, an oscillation vibration will be given directly to the antenna. However, since the oscillator is generally produced to a low power, disposed between the oscillator and the antenna usually for several amplification stages to increase the transmission power. Often not the frequency produced by the oscillator is used as a transmission frequency, but in particular at relatively high frequencies such as FM broadcasting, a harmonic wave, whose frequency is a multiple of the oscillator frequency. This is filtered out from the oscillation behind a Verzerrerschaltung in the form of an overdriven amplifier with LC elements and then amplified. In systems for frequency modulation or more frequencies voltage-controlled oscillators (VCO ) or oscillators according to the synthesizer principle used. In normal frequency transmitters, such as DCF77 carrier frequency of the transmitter is generated by an atomic clock and brought to the desired value by frequency division or multiplication -. Since this method is very costly, it is important for most plants do not apply - usually have crystal oscillators sufficient frequency stability.
The information to be transmitted, such as music or speech is imparted by modulating the carrier frequency.
As an amplifier elements are used particularly in high power amplifiers still electron tubes used. For microwave transmission systems are special semiconductor devices or transit-time tubes - such as klystrons or magnetrons - are used.
In the generation and amplification occur harmonics. These are not to be emitted via the antenna and must be suppressed by low-pass filtering. For small ranges of up to 20 m (remote control ) induction stations are also occasionally used.
Cooling
The output stages of transmitters of very small power do not require special cooling equipment. Tube amps are up to medium power ( 100 watts few ) often only radiation cooled. Medium power the convection air cooling ( semiconductor transmitter) or forced air cooling as in the image is used right. For great achievements since 1930, the water cooling the amplifiers ( tubes or transistors) is applied. Since high voltages are needed in tube amplifiers, is often distilled deionized water in the cooling circuit necessary. This water is from a heat exchanger transfers its heat to a second circuit, in which the water must meet any special purity requirements, since it does not come into contact with live components.
In high- power tubes today the Siedekondensationskühlung is applied. In this technique, evaporative cooling and condensation are spatially close together. The coolant flows through the cooling channel, which is provided with the anode inner side oriented grooves. In these grooves, the resulting steam gets into the main cooling passage, where it is vortexed and again condensed. Since this process takes place in the case of water at temperatures of over 100 degrees Celsius, only tubes can be cooled with this cooling method. The process works on the principle of a heat pipe. If in an evaporative cooling or a heat pipe heat carrier used with lower boiling point or lower pressure, including semiconductor transmitters can be cooled. Heatpipes allow the maintenance-free heat dissipation in a small space at high heat outputs. One application is, therefore, the cooling channels on board of spacecraft and aircraft.
Power supply
Tube transmitters require high anode voltages (of the order of 1 to 20 kilovolts ), which is generated by transformers and rectifiers. Often generators are available to be independent of the power grid.
Often transmitters to increase the security of supply or because of the high power from a higher supply voltage level fed. To be, or the major French TV channels Allouis and Roumoules, and Konstantynow in Poland were fed from the high- voltage network (110 kV in Allouis and Konstantynow, 150 kV in Roumoules ), although a power supply from the medium voltage level ( 20 kV) would have the power demand also can cover.
Antenna
The type of antenna is dependent on the frequency, the power and the desired directional characteristic. Mostly be for long waves umbrella antennas for long and medium waves self-radiating transmission towers, for short wave and ultra-short wave (FM ) and dipole antennas it uses existing array antennas. For the most directed radiated microwaves often parabolic antennas are used.
Antenna support for FM - and TV - stations are grounded. There are both guyed steel framework masts as well as free-standing steel and reinforced concrete towers are used, wherein the transmitting antennas are located at or near the top. Some transmitting towers for FM have high-altitude operating rooms and / or through tourist facilities such as restaurants and observation platforms, which are accessible via a lift. Such towers are usually called TV tower. For microwaves one frequently uses parabolic antennas. These can be set up for microwave applications on transmission towers for FM to special platforms. For the Programmzuspielung of television satellites and radio contact with spacecraft, large parabolic antennas with diameters of 3 to 100 meters in diameter are needed. Such systems, which can be used as a radio telescope, if necessary, are often designed to be movable.
When transmitting antennas for long and medium wave transmitter self-radiating transmission towers are most commonly used, which are either isolated from earth and be fed at the base or as grounded constructions are carried out, which are fed on risks of the backstays auxiliary ropes. Also Reuse antennas and long wire antennas on grounded towers and masts are used. Occasionally also T-, L- and delta patch antennas are used. Transmit antennas for long and medium wave are usually implemented as guyed masts. Similar antennas with smaller dimensions are used also for short wave transmitters, if these send in the round spray operation. For directional radiation mounted on free-standing steel towers Dipolwände be used.
For more information, see the transmitting antenna.
Protection circuits
Since transmitters of higher power large currents at high voltages can (up to 20 kV) flow and transmission equipment increased surge risk, are conditionally suspended by the most thunderstorm lightning exposed antenna support, comprehensive protection circuitry must be provided to secure the operation of the plant and to to protect system components as well as possible from destruction.
The transmitter must always be operated with a connected load ( antenna). If this is not a fault of the case, it must be switched off, otherwise the output stage can be destroyed. This includes the monitoring of the standing wave ratio, the ratio Umax / Umin along the high-frequency line. It must be close to 1 as possible, to keep the cable losses. Cause of a different standing wave ratio, defects in connectors to be at the antenna or the matching network.
In tube- equipped transmitters out the heater voltage must be applied to the tubes, the anode voltage is switched on only after heating. Otherwise, the tubes are subjected to increased wear.
Protection against lightning strikes is particularly at isolated standing radiating transmitting masts or transmission antennas of importance. Here is switched as coarse protection, a spark gap between the antenna and earth, which ignites at lightning. A fine protection grant additional gas-filled surge arrester. A monitoring device for the standing wave ratio switches the transmitter off briefly if the standing wave ratio is no longer true after a lightning strike ignited due to a trap. If the standing wave ratio, even after several switch-on attempts outside the norm, the transmitter remains switched off. In some transmitting plants are located at critical points and ultraviolet detectors that respond to pre-discharges or arcing and switch off the transmitter so that the arc is extinguished.
For water-cooled power amps the electrical conductivity of the water must be monitored and kept low. If it exceeds a certain value, the transmitter must be switched off and the water are exchanged.
Furthermore, the degree of modulation, the operating voltage, the transmission frequency and other operating parameters are monitored. The analysis is done either locally or from a remote control center, will be transmitted to the these values (wired or using the transmitted signal ).
Building
For large stationary plants is an appropriate building for the accommodation of the technical equipment needed the transmitter building. This building is usually designed as a purely functional building is located often 30 to 600 meters from the transmitting antenna from radiation- technical reasons for transmitters for FM and TV right next to the antenna support, for transmitters for long -, long-, medium - and short- wave. The transmission of the transmit power is usually done with a fish trap line or a coaxial cable.
Inter alia, in television towers, there is room to accommodate the transmission devices. Such structures are used for fixed radio links and FM transmitter.
Under or radiating transmitting masts there is often a building to accommodate the impedance matching ( matching network ) of the antennas.
Terms of Use
Since radio waves travel across borders, is for transmitters in frequency ranges where long ranges are possible, international coordination, as defined for example in Geneva wave plan necessary.
In Germany, the Federal Network Agency for Electricity, Gas, Telecommunications, Post and Railways controls this area.
An illegal radio transmitter is also referred to as Black stations.
Legal without a permit to be operated transmitters operate in the ISM bands, and must possess a type approval. As a radio amateur may be built its transmitter and the antenna system itself or change selling channels. The amateur radio service is the only radio service, where this is allowed. In the Radio Regulations Radio Regulations is enshrined internationally that radio amateurs in accordance with ITU Recommendation ITU -R M.1544 minimum theoretical knowledge of engineering, legal knowledge, the settlement of wireless connections ( the so-called industry) as well as electromagnetic environmental compatibility ( EMC-E ) and electromagnetic must have compatibility ( EMC). This knowledge must demonstrate a budding amateur radio in a test with its National Telecommunications Administration.
The CB radio is, however, up to certain maximum benefits fully private spaces.
Since February 2006 in Germany, the operation of transmitters (known as FM Transmitter) on the FM band ( band II) allows short range of a few meters up to 50 nW ERP for private purposes, such as for the transmission of signals an MP3 player to the car radio.
Planning
The planning of a transmitter system starts with the selection of the site. For the sake of EMF (protection from electro-smog) a minimum distance from residential buildings is observed, which depends on the transmission frequency and the type of the transmitting antenna.
Transmitter for long and medium wave frequency, built at a location of high electrical conductivity of soil to ensure good grounding. To this end locations at sea or in river valleys are ideal. Transmitters for FM builds to best increase, as these waves propagate quasi- optically. One can then provide power for larger areas.
A transmitter needs to be frequently operated with a limited directional diagram, not to interfere with other users. Examples are microwave links or communication channels of the railway.
Location information
It is common to specify the geographic coordinates of the location of transmission facilities. It is given the location of the transmitting antenna ( used in normal operation ). This is particularly important in beacons. When entering a place name that place was called, in whose bounds the transmission facility is located. This was not usually done in the former Soviet Union and the former Eastern bloc countries from obfuscation reasons - it was called the nearest large town. For transmitter systems on mountain tops, the name of the summit is usually called, but sometimes the district of the village, on which this peak is located. For this reason, there are numerous transmitter systems often multiple site names.
Cultural Significance
Some cities, such as Muehlacker, Ismaning, Langenberg, Rothsürben, Kalundborg, Hörby and Allouis were widely known as sites of powerful transmitters. Some transmitting towers like the Berlin TV tower or Fernsehturm Stuttgart became landmarks of cities. Many transmitting plants have very high antenna support, the realization of which was often a constructional maximum performance. They are therefore also listed in the category High Buildings.
Records
- Highest transmission tower 1974-1991, Radio Warsaw radio mast in Konstantynów 2000 kilowatt longwave transmitter, 648.38 m
- 1963-1974 and since 1991, KVLY Tower 628.8 meters
- Highest transmission powers Long wave transmitter Taldom 2500 kilowatt
- Medium wave transmitter Bolshakovo 2500 kilowatt
Radio stations
The term " radio station " means, in addition to the station and the program (see radio), also a special transmitter, the music, voice or data by means of a modulator modulated onto a transmit frequency, amplified and an antenna feeds (see broadcasters). Thus, signals can be transmitted over long distances and are equipped with a radio receiver.
In Germany the operation required (not the building ) a transmission system for the purpose of broadcasting a permit from the competent state media authority.
As an FM transmitter is called very weak, such as a VHF transmitter frequency modulated transmitter. They are used for the transmission of music and speech over short distances and can be received with FM receivers. Find application such radio stations such as in a car or movie theater within our own cars to feed an MP3 player in your own car radio.