Medium wave
The term medium wave broadcasting refers to broadcasting in the medium wave band ( to the receivers often with AM or AM refers ). This corresponds to the frequency range between 526.5 kHz and 1606.5 kHz. The transmitters use this field in a 9- kHz steps. In the Americas, the medium wave band covers the frequency range 530-1720 kHz. Are used, the frequencies in a 10 kHz channel spacing.
Broadcasting on medium wave is now used predominantly, the terrestrial broadcasting of radio programs over the coverage area of the FM station. In addition, he is, as well as the short-wave broadcasting, used for the transmission of foreign-language programs to listeners in other countries. Occasionally used for medium wave broadcasting and the broadcasting of news programs such as NDR Info or particular other word -heavy programs, because this sound quality degradation over FM are easier to cope with; this in view of the limited frequencies in the VHF range. In some areas of the world the medium wave is also used for transmitting local programs, but to a decreasing extent.
History
In the early years of broadcasting in the 1920s, the central shaft was the principle used medium. Only with the development of more powerful transmitters, other wavebands could be put to good use. At the time, the channels were normally distributed ( in addition often the frequency in kilohertz ) specified with the wavelength in meters. The sole indication of the frequency prevailed until later.
Station list on the front panel of a German radio in 1956, (L long wave, medium wave M, K shortwave, VHF Very High Frequency )
Technology and propagation conditions
Because of the small number of available transmission channels for broadcasting in the medium wave range (121 channels), each frequency is occupied in this area from multiple transmitters. The medium wave frequencies 1485 kHz, 1584 kHz and 1602 kHz are reserved by the Geneva wave plan as so-called Community waves for the operation of low-power transmitters in sufficient mutual distance.
Because of the large range of space wave during the night hours must, as specified in the Geneva wave plan rules to reduce mutual interference, many powerful stations reduce their transmit power and / or work with a directional antenna (see longwave broadcasting ). Some stations must cease operations entirely during the night hours. Nevertheless, occur on many channels in the medium-wave band at night by the simultaneous reception of multiple channels often gleichfrequenter interference ( interference ) on. With a unidirectional receiving antenna as a ferrite loop antenna, or you can remedy the situation by turning the antenna if both transmitter does not radiate from the same direction.
The transmission frequencies of the transmitters are located in Europe, normally on by 9 divisible without remainder frequencies. In areas with a 10 - kHz step the values for the transmit frequency to be used analogously that are divisible by 10. There are and were some radio stations in the medium-wave band, which were operated outside the official medium wave range. Bayerischer Rundfunk used until 1999 for its low-power transmitter in Hof Würzburg and from the off- center shaft radio frequency range 520 kHz. At 523 kHz, the coast station Klaipeda Radio / LYK and thus officially in the medium wave segment of the maritime radio worked.
Digitization of the central shaft
Meanwhile, trying to counteract the action is going in the field experiment digital medium wave (Digital Radio Mondiale ) the inferior sound quality and the low popularity in Europe. In some countries, stereo broadcasts are transmitted by the AM stereo process in the medium-wave band.
AM stereo is not applied in Germany. In the United States, South Africa and Australia it is widespread. In Europe, the process is used by the night -air in Germany transmitters of Radio France on 864 kHz in Villebon -sur -Yvette and the Italian Radio Studio X on 1584 kHz.
Perspectives
According to a European Commission decision of analogue broadcasting, and thus the center shaft should be turned off until the beginning of 2012 in all Member States. However, after 2012 send a series of analogue channels further, as for the technical successor DRM beside reception solutions using a PC very few portable receivers are available to date (as of 2012), but they are bulky and have a relatively high power consumption. In addition, not (yet) sufficient DRM transmitter infrastructure is in place (see analogue "switch - off"). In Germany, the frequency allocations for AM broadcasting, however, expire on 31 December 2015.
Global plays the medium wave broadcasting in the countries of the southern hemisphere (Africa and South America ) play an important role. In many countries, the FM radio network there is poorly developed and the center shaft has the advantage of large-scale transmission and simple receptivity for the handset.
In the U.S., traditionally a number of private medium-wave stations still in operation.
Selected medium-wave transmitter in amplitude modulation
List of transmission facilities that are largely received in Germany:
05.15 clock - 05.45 clock religious programs of various mission agencies
05.45 clock - 08.00 clock RTL Radio
08.00 clock - 13.00 clock Radio China International ( German ) ( 09.2013 ) ( 7/7)
13.00 clock - 18.15 clock RTL Radio 18.15 clock - 18.30 clock religious programs of various mission agencies 18.30 Clock - 19.15/19.30 clock RTL Radio 19.15/19.30 clock - 20.00 clock religious programs of various mission agencies 20.00 clock - 01.00 clock Radio China International ( German )
Through numerous shutdowns of powerful radio stations (as of 2013) can significantly fewer radio stations are received as 25 years ago in the medium wave range today.
Selected medium-wave transmitter in DRM mode
Historic medium-wave transmitter
List switched off transmitter systems, a rich history and a transnational awareness exhibited in part: