Radboud Current Astronomy Picture

On July 15, 2011 the TV & Radio communication tower at Hoogersmilde in the province of Drenthe caught fire and eventually collapsed. This caused a major disruption of TV and radio service 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 antenna 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 was taken through the side-lobes of the antennas and through a low-pass filter to suppress the FM band, so is highly suppressed, but nonetheless clearly visible.

While Hoogersmilde was the strongest source of transmission 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.

Credit: H.Falcke, S. ter Veen