Being a radio telescope, and extremely sensitive radio receiver, sources of interference are a real issue. The rather isolated location helps greatly, but the number of electronic devices generating interference is proliferating, especially at the signal levels involved. A sign at the entrance asks visitors to turn off mobile phones and video cameras. I suspect digital still cameras will be added to that list too.
This structure is used to detect nearby radio sources to allow the telescope operators to discount them from their observations. Details of its operations are shown below from the CSIRO display board alongside the cabin.