Digital Signal Processing Reference
In-Depth Information
coaxial cables. The very first transmitter cable was pulled up unwound on
the rail by the rack railway in a "special action" at the beginning of the fif-
ties. The new cables were flown up the mountain by helicopter, among
them the last UHF cable which, with a diameter of almost 20 cm, is the
thickest cable ever used on the Wendelstein mountain. One cable is used
for the VHF band and one is used for the UHF band, and the third cable is
a spare for emergency cases.
Such coax cables have approximately the following attenuations over
100 m length in each case:
Table 31.3.
Technical parameters of HELIFLEX (©RFS) coax cables
Diameter of
the coax
cable
Max. avg.
power
at 500 MHz
Att. [dB] at
200 MHz
Att. [dB] at
500 MHz
Att. [dB] at
800 MHz
4-1/8''
35 kW
0.4 dB
0.7 dB
0.9 dB
5''
55 kW
0.3 dB
0.5 dB
0.7 dB
6-1/8''
75 kW
0.3 dB
0.4 dB
0.6 dB
8''
120 kW
0.2 dB
0.4 dB
0.5 dB
At the top, at the solar observatory and the meteorological observatory
of the German Meteorological Service (Deutscher Wetterdienst), there is
also the so-called antenna house from which the cables are then run to the
actual transmitting antenna. It contains another patch panel via which the
upper and lower half antenna of the transmitting antenna can be selectively
fed or disconnected both in the VHF band and in the UHF band. If neces-
sary, this is done via 20 cm-large coax-type U-links.
The antenna itself consists of the following components by Kathrein,
Rosenheim, which are housed in a FRP (fiber-reinforced plastic) cylinder.
The FRP cylinder has a total height of approx. 24 m and the antenna as a
whole is appr. 65 m high; the tip of the antenna being about 1900 m above
sea level.
The VHF antenna is composed of 6 levels with 6 vertically polarized
Band-III dipole antenna arrays. The bottom 3 levels form the lower half
VHF antenna, the upper 3 levels form the upper half VHF antenna. Both
half antennas are supplied via their own feed cable each. The UHF antenna
consists of 12 levels with 8 Band-V/V antenna arrays each which, just like
the VHF antenna, is built up from the lower and upper half antenna (with 6
levels each in this case). Here, too, each half antenna is driven by its own
coaxial cable. Above the UHF antenna, there is the mechanical vibration
absorber which is intended to prevent oscillations in the case of wind load-
ing.
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