Tracking down interference

Responsible for identifying and resolving interferences to signals and radiocommunications services, members of the ACMA’s Field Operations Section spend much of their time on the road and on a mission.

When the team was called to investigate an incident affecting Queensland Urban Utilities (QUU), they took with them a Rohde & Schwarz PR100 receiver to help track down the interference.

QUU contacted the ACMA’s Brisbane office to report severe interference to their water distribution and sewerage control system in the south-west of the city.

Its point-to-multipoint system consisted of a base station and some 90 remote sites. The system had not worked correctly for more than 24 hours and technical officers were so concerned about the situation they requested a change to the licensed frequency.

A temporary licence was arranged with the help of Mark Williamson, senior frequency assigner at the ACMA.

The alternative frequency allowed QUU to move off its affected frequency but also meant that its technicians now needed to visit the 90 remote sites to reprogram the new frequency.

As this process would take days, the priority remained to identify and fix the interference.

The task was allocated to field operations officers Cameron Bell and Michael Cooper.

As a matter of course before leaving the office, the team used the in-house monitoring equipment to hear the interfering signal and get a direction to it. They then left to meet a technical officer who connected the ACMA’s equipment to the QUU antenna so the characteristics of the interfering signal could be seen.

Since the interfering signal had already been seen with the ACMA’s equipment, Bell and Cooper made their way to the highest spot at the base station where they were able to obtain a bearing on the signal.

Armed with the bearing, they began searching for the signal’s location.

Using the newly purchased Rohde & Schwarz PR100 receiver and its associated aerials, the team followed the signal through the south-western suburbs, stopping every now and then to reassess the situation.

Eventually they located a Brisbane City Council water pumping station between the base station and Mount Coottha and it was from here that the team believed the interfering signal was being transmitted.

As they drove past the station, the signal reduced significantly, which confirmed their suspicions.

The team then called a QUU technician, who met them on site to switch the transmitter on and off and confirm they had found what they were looking for.

The antenna at the pumping station was very directional towards the base station, explaining why the QUU technicians were unable to see the interfering signal from there the previous night when they had attempted to locate the signal.