Mediumwave transmitter Mainflingen

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The Mediumwave transmitter Mainflingen (Mainflingen C) is a medium wave transmission facility south of the A3 motorway near Mainflingen, Hessen, Germany. Mediumwave transmitter Mainflingen was the first mediumwave transmitter for Deutschlandfunk. It went in service with a transmission power of 50 kW in 1962 on the frequency 1538 kHz at the upper end of the mediumwave band. This frequency has a bad groundwave propoagaton and therefore a low range at daytime, but an excellent skywave propagation with a long range atnight time. Already in December 1962 the transmission power of Mainflingen mediumwave transmitter was increased to 300 kW. Until 1967 its antenna was on the same site, where all long wave transmitters of Mainflingn worked. This resulted in interference problemes, which made the desired further increase of transmission power impossible.

So a new transmitter with a directional and an omnidirecional antenna was built in the Mid of the Sixties on a site south of the motorway A3 in a distance big enough to the longwave transmitters that even when using a power of 1000 kW no greater interference problemes would occur. This facility went in service on January 1, 1967. As well the directional as the omnidirectional antenna were somewhat unusual for mediumwave broadcasting antennas. The omnidirectional antenna consisted of a ground-fed 142 metre tall guyed mast carrying a double conical cage antenna with 64 metres diametre. This construction allowed its usage for all medium wave frequencies and therefore also as backup antenna for the mediumwave transmitters of Deutschlandfunk at other sites. The directional antenna consisted of two horizontal dipoles which were mounted on 4 85 metre tall guyed masts in a height of 75 metres with a radiation maximum showing in Northeast and Southwest direction. As the omnidirectional antenna could not be used for the whole transmission power of 700 kW which was available after January 1, 1967 ( a transmission power of 1050 kW was also possible by switching the third backup transmitter in parallel, but of economical reasons never used) in 1974 a 95 metre tall guyed ground-fed mast radiator was built. The transmitter was now run at daytime with 700 kW and omnidirectional radiation and at nighttime with directional radiation and 350 kW and used at evening time for transmitting also English speaking programmes. The invention of the waveplan of Geneva resulted just in an incraese of the transmission frequency from 1538 kHz to 1539 kHz. Its daily operation mode was not affected. However, it was not allowed according to the waveplan of Geneva to use the double conical antenna any more as backup antenna for mediumwave transmitters of Deutschlandfunk at other sites ( the regulations of waveplan of Geneva do normally not allow operation of backup transmitters more than 50 kilometres away from the standard site without special coordinative measures) and so got this antenna, which got to a landmark of the station obsolete and was dismantled in 1982. After March 1, 1983 the program of Deutschlandfunk was also at night time radiated with omnidirectional radiation. The directional antenna with its 4 masts was dismantled afterwards. After April 1, 1988 the transmission power was reduced to 350 kW. Beside the bad groundwave propagation of the used frequency, mediumwave transmitter Mainflingen was in spite of its high power only in a small area well receivable at day time. This resulted in a shut-down of the transmitter on December 31, 1994, after the transmissions in foreign languages were already cancelled a few years ago.

As replacement the transmitter Heusweiler of the Broadcasting Company of Saar County (German: Saarländischer Rundfunk) was leased. First it was planned to demolish the facility, but on April 1, 1996 Evangeliumsrundfunk, a religious broadcaster, which hired already transmission time at Trans World Radio restarted its operation.

Several disputes between Telekom and Mainhausen community started, as after relaunch of transmitter problemes with electromagnetic influence at electric device started and the community does not want to enlengthen the treaty for using the transmission site. In 1998 it was achieved, that the site could be used further for mediumwave transmission and modernization of the facility started. First the old transmitter was replaced by a new full transistorized, which would be also able to operate in DRM mode.

In order to allow a good nighttime transmission without causing too much trouble with eectromagnetic influence, at the beginning of 2006 a cross dipole antenna with a radiation maximum pointing vertically in the sky was built. This antenna, which is one of the few applications of circular polarisation for broadcasting is mounted on 5 guyed masts. The central mast of this antenna is grounded. It carries the feeder cables running to the dipole, while the masts at the edge are standing on insulators and grounded via inductances in such way, that they radiate as less high frequency as possible. By this undesired parasitic radiations causing trouble at electrical device of people living near the site are suppressed. It is also interesting to know that the radiated wave must be right-hand polarized. Otherwise the signal reflected on the ionosphere would be 20 dB less strong. In spring 2006 this new antenna went in service. It is used only for nighttime transmissions, as the desired ionospheric reflection occurs only at night. At daytime further the old mast is used as antenna.

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