R 31375 The Base interference report F.pdf

under the
Released
Official Information Act 1982

Findings
After discussing the likely cause to be their legacy wireless car-park monitoring system the location
of the source was quickly located. Transmitting on 433.92 MHz the source was from the rooftop of
the main complex where a control box was located.
The Facilities Manager called in an electrician to isolate the power to the control box. The electrician
discovered the programmable logic controller (PLC) may have caused the TX relay to latch on after
the power was restored.
Conclusions
The source of interference was identified to be the shopping complex’s legacy wireless car-park
monitoring system that was not fully decommissioned. Once the power was isolated the
interference ceased.
After visual examination, the transmitter module (25 mW) and together with the antenna system
was estimated to be within the maximum allowed radiated power limit (-16 dBW eirp) as prescribed
in the General User Radio Licence (GURL) for Short Range Devices.
The transmit frequency 433.92 MHz was also observed to be within the GURL band limits. An audit
of the transmitter module to determine compliance to a radio standard and the transmitter system
to determine the exact level of radiated power may be considered.
under the
Released
Official Information Act 1982
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Case: 31375