Mainflingen DCF77 Tx Site
In December 1999 the Tech. University of Darmstadt made an excursion to the Mainflingen Tx Site which is operated by the Deutsche Telekom. Mainflingen is a longwave transmitter site, which was converted from an old airfield after WWII. It is located approx. 35km SE of Frankfurt/M., the antennas are visible from the nearby motorway A3 (Frankfurt - Nuernberg).
From the 12 available antennas only a few are in operation nowadays. Three transmitter are in use:
The well known timesignal DCF77 is transmitted on 77.5 kHz with a power of 50kW. The timesignal is generated directly on site in Mainflingen, not at PTB Braunschweig, as i thought before my visit. Although, the operational responsibility for the "clock" lies with PTB Braunschweig.
DCF49 on 129.1 kHz (100kW) is used to remote control electric power distribution grids throughout Germany. It's reported that it uses 200Bd ASCII codes. Transmitted data is supplied by the participating power companies via landline. An alternate transmitter for that use is located in Burg in east Germany, transmitting on 139.0 kHz.
The third transmitter is used for broadcasting a differential GPS signal on 124.5 kHz, power?
During the visit I took some pictures, but unfortunately the weather was rather bad. Therefore I don't have any good pics of the antennas, at least not good enough to show them here.
A very nice model of the site gives a good overview of all antennas and buildings. Unfortunately it's too large to be shown in one pic. (Or my camera is too bad :-)
The antenna masts are between 150 and 200m and are not used as antennas but just to support the wire antennas. The antennas itself are vertical wirebundles, held by horizontal wires. These horizontal wires act as roof capacities.
On site are still a lot of old transmitters, which are not in use. Beautiful to look at, and still working, if necessary. This picture shows a tunable loading coild in the final stage.
The same transmitter, the final stage with two tubes. If i remember correctly it has a power of 20kW.
A more modern transmitter, final stage. THat's the 20kW(?) TX used for the DGPS signal. The glowing tube can be seen in the back, the colorful discs are ceramic capacitors.
This is the DCF77 TX, 50Kw. It's an aircooled solid state TX with 50 semiconductor modules, each @1kW (visible behind the windowed door). They are combined on a power coupler backplane. The closed racks to the right contain the matching network for the transmission line. Manufactured by Telefunken.
The two ERF transmitters in the same technology (2 x 100 semiconductor modules @1kW). One tx is in operation, the other on stand-by for backup.
The control panel for the 100kW ERF transmitter.
This is the actual DCF77 clock, located in the basement of one of the old transmitter buildings. It uses two HP caesium clocks and a third atomic normal, specifics unknown. This "clock" is designed and operated by the PTB (Physikalische Technische Bundesanstalt) in Braunschweig. The racks to the left contain the coding logic, the modulator etc.
For more information on DCF77, the PTB etc. see the website of PTB.