| On July 15, 2011 the TV & Radio communication tower at Hoogersmilde (aka the Smilde tower) in the province of Drenthe caught fire and eventually collapsed. The tower was almost 300 m high and was the second highest tower in the Netherlands. The collapse caused a major disruption of TV and radio services in the Netherlands.
The tower is located in the same province as the LOFAR radio telescope, which was operational at the time measuring radio emission from cosmic particles for the LOFAR Cosmic Ray Key Science project using the transient buffer boards (TBBs). The TBBs allow one to record raw data from all antennas and do offline processing after an event has happened. The figure shows three radio spectra from low-band antennas (LBAs) in the FM band with 1 kHz resolution right after the fire had started: during the fire the signal strength goes down and then shuts off completely. The data were taken through the side-lobes of the antennas and through a low-pass filter to suppress the FM band, so are highly attenuated, but the transmissions are nonetheless clearly visible.
While Smilde was the strongest source of transmissions at low frequencies, it had not caused major problems in LOFAR data since proper measures had been taken to mitigate its radio frequency interference (RFI). In fact, the LBA frequency range is rather free of RFI. This is different from the WSRT, where the Smilde tower caused major RFI near 50 cm (digital TV). Astron astronomers are working very hard to profit from the demise of the Smilde tower and observe in WSRT bands normally not accessible... Stay tuned....
|H. Falcke & S. ter Veen (Radboud Univ. & ASTRON)