GPS antenna problems

A member has reported a serious failure of a vessel’s GPS positioning equipment. When approaching the work area, which was close to the shore, the vessel experienced a complete failure of all its GPS receivers (eight receivers from four different manufacturers/suppliers).

Following extensive fault-finding which isolated the problem to the area of the vessel bridge, it was discovered that one GPS unit was causing the failure of all the other units. The receiving antenna for the unit had failed and had become a transmitter, the signal from which subsequently blocked all the other GPS receivers mounted nearby. The close proximity (<1m) of this damaged antenna unit to two other GPS antenna units may also have caused damage to the internal electronics of these units.

Members are warned to be aware of the potential hazard posed by a faulty GPS antenna and that all GPS antennae be separated by at least two metres where possible. It is recommended that when selecting the mounting location and installing global navigation satellite system (GNSS) antennae, guidance is taken from the system manufacturer with regard to safe operating distance from other equipment and with special attention given to transmit/receive devices. Care should also be taken in the selection of appropriate cabling and antennae and to the shielding and grounding required for these systems. A regular inspection and maintenance schedule is also recommended, with periodic replacement of cables.