Sebastian, Matthias and I decided to stop at the shortwave station in Moosbrunn, Lower Austria while driving to Graz. In recent years, this station became well known for transmitting Radio DARC with a power of 100kW on Sundays. We only took some photos of the antennas because we were short on time but hope that we will come back one day to see the transmitter building from the inside. I will show and describe some antennas in this article and you can also download all photos.
The station has five antennas today:
- Dipole array for east / west transmission
- Rotatable dipole array
- Logarithmic periodic antenna
- Horizontal cage antenna (Quadrant antenna)
- Vertical cage antenna
Dipole array for east / west transmission
In this picture you can see a directional antenna which allows you to transmit to the west or the east.
The antenna consists of three layers: One Reflector grid in the middle and one dipole array on each side. By switching between the dipole arrays the radiation direction can be selected. This antenna can’t be turned but there is also a similar antenna on tracks that can be turned in any direction.
Closeup of the dipoles.
The boxes in this picture are baluns. They convert the earth asymmetrical signal from the coaxial feedline (big tubes coming from the ground) to a symmetrical signal which is used to feed the dipoles.
Rotatable dipole array
This is the rotatable antenna. It also consists of three layers. On one side of the reflector the higher frequency dipoles are mounted and on the other side the lower frequency dipoles are fixed. A faded sign next to the antenna reads: Frequency range: 6 to 9 MHz and 11? to 21 MHz, Maximum Power: 500kW, Gain: up to a 20db(i/d?), Beam width: 19-34°, Weight: 320t (metric), Time for one full rotation: 8 minutes
Here you can see how the dipoles (marked by red lines) for the lower frequencies are mounted in an array of 2 x 3. The feedlines (twin leads) are marked with orange arrows. It is observable that the distance between the wires of the twin lead changes at some point. This indicates a change of the cable impedance and is used for antenna matching. Moreover, sometimes there are double connections (back twin lead is connected to front twin lead at two points). This is also used for matching.
On the other side of the reflector grid, the higher frequency dipoles are placed. Since they are smaller more of them can be mounted which leads to an array of 4 x 4 dipoles. Again, the dipoles are marked in red and the feedline path is marked in orange arrows.
The antenna sits on train track.
Logarithmic periodic antenna
Big logarithmic periodic antenna.
Horizontal cage antenna (Quadrant antenna)
On the left side you can see two horizontal cage areals (Reusenantenne, this form: Quadrantantenne) consisting of right angle dipoles.
Edit: I was wrong these aren't directional antennas. They are unidirectional in the horizontal dimension. In the vertical dimension the antenna radiates at about 35°. One of the two antennas is mounted higher and has a longer dipole because it is designed for a lower frequency.
On the right side a vertical cage areal is visible.
Switch box of the cage areal.
Switch box of the cage areal and the twin lead feedline.
Vertical cage antenna
This must be one of the oldest antennas in Moosbrunn. It’s a vertical cage antenna.