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Bremen
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MW antenna Bremen-
folded monopole without tuning unit
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The station was shut down on the
10th of March 2010.
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MW antenna Bremen 936 kHz,
50 kW with flare skirt and
no antenna tuning unit
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Photo above was copied with the friendly authorisation by Heinz Schulz.
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MW antenna Bremen - description
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The MW programme of Radio Bremen is transmitted from this antenna since 30th of April 2002.
This transmitting antenna is a vertical folded monopol with the following properties:
- short mast
- grounded mast
- 50 ohms - input impedance without
antenna tuning unit
The grounded square mast ( 45 m high ) is guyed three times every 120° at the top and approx. in the middle of the mast. The guy ropes (Pardune) are intersected by egg insulators. The design of the head of the mast allows to fix two ropes as top load (Dachseil) and a flat cage (Reuse) additionally, all three every 120°. These three elements of the antenna are suspended by an angle of 45° towards the ground.
The two ropes of the top load are interrupted by a rod insulator at a height of 12 m above ground.
The flat cage is bended at a height of approximately 15 m, guided towards the base of the mast, and connected to the ground by an insulator. This is the feeding point (Einspeisepunkt), where the feeding cable (50 ohms) is connected, the inner conductor to the flat cage and the outer conductor to the foot of the mast.
The mast and the bended flat cage represent a folded monopol with a transformation ratio of a little bit less than 4:1 compared to a base fed vertical radiator. By adjusting the length of the top load it is possible to tune the antenna impedance to Z = 50 + j 0 ohms. A ground net of 60 radials each 50 m long reduces the ground losses.
The omnidirectional radiation (minimum reception fieldstrength 63 dBmV/m) of the ground wave is approximately 120 km for an good ground conductivity (10 mS/m; er=4) and 230 km for a very good ground conductivity (30 mS/m; er=4).
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 For enlarging click on photo
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 For enlarging click on photo
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Technical data:
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Power:
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50kW
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Frequency:
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936 kHz
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Bandwidth:
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± 4.5 kHz
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Input impedance:
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50 ohms, no antenna
tuning unit
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Standing wave ratio referred to 50 ohms for carrier frequency:
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1.05
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Gain referred to
l/4 vertical monopol:
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0 dB
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Radiation pattern:
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omnidirectional
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Height of mast:
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45 m
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Radius of ground net:
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50 m
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Antenna material
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Aldrey (seawater
resistant AI)
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Material of ground net:
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3 mm Cu
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Lightning protection:
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spark gaps at feeding point and grounding of mast
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Guys:
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galvanized steel ropes intersected by by egg insulators KER220
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Google map may be
enlarged,
diminished,
shifted,
switched to satellite view
etc..
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The exact location on the
"green Meadow"
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Aerial view of the antenna
The broad cage can be recognized very well.
The transmitter building at the top of the photo.
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Bremen
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