Installation Manual

S4-2 89-041 Section 4 Issue 5
protocol converters or frequently as repeater instruments for the sensor. A Gyro Interface Unit,
P/N 89-028, is available from McMurdo as an optional extra.
VHF and GNSS (GPS) antenna cable connections
The VHF and the GNSS antenna cables are connected directly to the transponder through a
UHF and a TNC plug respectively.
The coax cable plugs must be attached directly to the cables; the outer insulation must not be
connected in the cable cleat but in the coax plug as illustrated below.
VHF antenna
The VHF antenna is an important part of the receiver and transmitter system; the reception
range is heavily dependent on the antenna installation. It is recommended to use an omni-
directional vertical polarised VHF antenna with a gain of 3 – 5 dB. The VHF antenna must be
installed as high as possible and free of shadow effects from the ship superstructure; effective
installation will maximise the range of the system.
In accordance with the IMO guidelines, an exclusion zone is defined around a VHF antenna;
other antennas must be mounted outside this zone.
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 or N-type connectors.
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 150MHz, thus the signal
strength is reduced to half its value due to cable attenuation.