Installation Manual

AIS Installation Manual Issue 1 21
6.3.1 VHF antenna
To make sure that the transmitted and received VHF signal is not interfering with Radar signals,
other VHF transmission or power lines it is important that the connection between the VHF
antenna and the transponder is of a high quality double shielded coax cable. It is recommended
to use a RG214 cable and PL259 connector.
If the cable has to be longer than 40 metres, it is recommended to use a cable with lower loss; a
40 metre RG214 coax cable has a signal attenuation of 3 dB at 150 MHz, thus the signal
strength is reduced to half its value due to cable attenuation.
Detailed instructions for fitting the connector are provided with the installation kit. The illustration
shows the preparation of the cable and the components of the connector.
6.3.2 GNSS (GPS) antenna
The GNSS operates in the ultra high frequency band (1.575 GHz). The signal attenuation in
cables is therefore substantial and has to be taken into account when the coax cable between
the antenna and the AIS unit is chosen. To compensate for signal attenuation the supplied
GPS antenna includes a pre-amplifier with a gain of 30 dB.
The cable attenuation should not be greater than 30 dB for optimum results, because the aim is
to have a total signal loss of less than 0 dB. The table shows the attenuation and the
recommended maximum length of two types of coax cable.
Cable description Attenuation / 100 metres
@ 1.5 GHz
Recommended
maximum cable length
RG 58 70 dB 40 metres
RG 214 37 dB 80 metres
Connectors used must be TNC throughout.
Detailed instructions for fitting the connector are provided with the installation kit. The illustration
shows the preparation of the cable.
Connector
body
“Top hat”
Plastic sleeve
Gland nut