Broadcast transmitter
A broadcast transmitter is an electronic device that radiates radio waves modulated with information content intended to be received by the general public.
Each transmitter is assigned a unique identifier consisting of a string of letters and numbers called a callsign, which must be used in all broadcasts.
Since some authors take account of gain factors of aerials of transmitters for frequencies below 30 MHz and others not, there are often discrepancies of the values of transmitted powers.
However, a broadcast transmitter with a megawatt power stage transferring 98% of that into the antenna can also be viewed as a 20 kilowatt electric heater.
Very high-power tubes of small physical size may use evaporative or vapor cooling by water in contact with the anode.
The output stage must be monitored for standing waves, which indicate that generated power is not being radiated but instead is being reflected back into the transmitter.
This consists of spark gaps and gas-filled surge arresters to limit the voltage that appears on the transmitter terminals.
In some transmitting plants UV detectors are fitted in critical places, to switch off the transmitter if an arc is detected.
The operating voltages, modulation factor, frequency and other transmitter parameters are monitored for protection and diagnostic purposes, and may be displayed locally and/or at a remote control room.
In the United States, broadcast and industrial transmitters are regulated by the Federal Communications Commission (FCC).
In Australia transmitters, spectrum, and content are controlled by the Australian Communications and Media Authority (ACMA).
As in any costly project, the planning of a high power transmitter site requires great care.
Transmitters for long and medium wave require good grounding and soil of high electrical conductivity.
Similar antennas with smaller dimensions are used also for short wave transmitters, if these send in the round spray enterprise.
Some transmitting towers for UHF have high-altitude operating rooms and/or facilities such as restaurants and observation platforms, which are accessible by elevator.
For example, large parabolic antennas ranging from 3 to 100 meters in diameter are necessary to pass on signals to television satellites and space vehicles.
Once the Digital Switch Over (DSO) occurs the plan is that most transmitters will revert to their original groups, source Ofcom July 2007.
Further complication arises when adjacent transmitters have to transmit on the same frequency and under these circumstances the broadcast radiation patterns are attenuated in the relevant direction(s).
Main stations are defined as those that generate their own modulated output signal from a baseband (unmodulated) input.
Some cities in Europe, like Mühlacker, Ismaning, Langenberg, Kalundborg, Hörby and Allouis became famous as sites of powerful transmitters.
An example is the Ostankino Tower in Moscow, which was completed in 1967 on the 50th anniversary of the October Revolution to demonstrate the technical abilities of the Soviet Union.
KVLY-TV's tower located near Blanchard, North Dakota was the tallest artificial structure in the world when it was completed in 1963.
