VHF Direction Finding (VHF DF)

VHF Direction Finding was originally used by VTS Operators to assist in identifying which vessel was calling the VTS Centre. However, since the deployment of AIS, all AIS equipped Ships have been broadcasting their identity at regular intervals and VTS Centres have been reading this identity to assist the VTS Operator in identifying all vessels. Therefore, the uses for VHF Direction Finding within a VTS system has now changed as it is only those vessels that do not have an AIS transponder that this sensor can now help to identify.

But identification of unknown vessels is not the only role of VHF DF. In a complex VTS area where there are many AIS equipped vessels on the VTS Operators’ screen, it can still take some time for the Operator to find the relevant Vessel ID on his Traffic Display screen. VHF Direction Finding provides an on screen bearing line to indicate the direction of the source of a VHF transmission. This quickly directs the VTS Operator to the location of the vessel with whom he is communicating. It can therefore provide value as an aid to the VTS Operator in complex vessel traffic situations.

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In the Coastal Surveillance domain, Communications Direction Finding still has a role as it can be used to detect voice communication which could assist law enforcement activities. VHF and / or UHF Direction Finding could help to identify the participants involved in illegal / smuggling activities and through the use of multiple DF sites, could enable triangulation on the source of a suspicious transmission. As such targets are likely to be small, fast moving craft that may be designed to avoid radar detection, the Direction Finding equipment could help guide Interdiction forces to their target.