Blaw Knox transmission tower
A Blaw Knox transmission tower is a guyed, self-radiating transmission mast for medium waves in the form of a double pyramid . The Blaw-Knox transmission tower functions as a self-radiating transmission mast isolated from earth , the length of which usually corresponds to about half the emitted wavelength.
history
The steel construction company Blaw-Knox, founded in 1917 in Blawnox near Pittsburgh , Pennsylvania , added transmission masts to its product range in 1927 and quickly developed several innovative antenna variants that tried to solve existing technical problems.
On June 30, 1930, a patent was applied for the type of transmission mast designed as a double pyramid. In their patent specification, the developers cite the most important feature that, due to the stable construction of the mast, it only needs to be guyed in one level, which avoids that too much transmission energy is diverted into the ground via the previously often guyed masts on the ropes. Apparently the guy insulators used at the time , which had to withstand very high loads, still had an insufficient insulation effect.
The patented features also include a mast tip that can be retracted and extended with the help of an electric motor in order to enable optimal coordination with the transmission frequency.
As a result, numerous transmission masts of this type were built in the USA, but also in Europe. The first system in Europe using Blaw-Knox transmission masts was built in the winter of 1932/33 on Bisamberg near Vienna . A special feature of this system was a passive reflector mast of the same type, which was 115 m away from the transmitter mast. The two masts were each 130 m high. Operations began on May 28, 1933, and on April 13, 1945, the two masts were blown up by withdrawing SS troops.
A few Blaw Knox transmission towers have survived in both the US and Europe. The design of the Bratislava TV tower is very similar to that of a Blaw Knox transmission tower.
Amateur radio associations such as International Amateur Radio Union , DARC , ÖVSV , USKA often have a diamond-shaped logo.
Europe
- Bisamberg , Austria (2 masts each approx. 130 m high: transmission mast erected in winter 1932/1933 and in operation from May 28, 1933; erection mast erected in autumn 1933; both were destroyed by war on April 13, 1945)
- Lakihegy , Hungary (year of construction: 1933, altitude: 314 meters)
- Lisnagarvey , Northern Ireland (year of construction: 1936, height: 108 meters, upper part shortened (original height 144.8 meters))
- Stara Sagora , Bulgaria (year of construction: 1936, height: 88 meters)
- Wakarel , Bulgaria (year of construction: 1937, altitude: 215 meters)
- Ulbroka , Latvia (year of construction: 1947, height: 125 meters, blown up in 2010)
United States
- WSM , Nashville , Tennessee - 246 m, built in 1932; originally 267 m; Tower stands in Brentwood , Tennessee.
- WLW , Cincinnati , Ohio - 227 m, built in 1934; Tower is in Mason , Ohio.
- WBT , Charlotte , North Carolina - three towers each 130 m high, built in 1934 (west mast) and 1945 (both other masts, west and east masts reconstructed after destruction in 1989 by Hurricane Hugo )
- WFEA , Manchester , New Hampshire - 121m , built in 1931
- WBNS , Columbus , Ohio - 116 m