Thrane&Thrane SAILOR 6249, Installation Manual

Page: 36 / 88

VHF antenna installation
2-16 Chapter 2: Installation 98-133942-
A
2.4 VHF antenna installation
The SAILOR 6249 VHF Survival Craft must be installed with one antenna for VHF RX/TX
communication. You can install all commonly available 50 Ohm antennas covering the
appropriate frequency range and providing a VSWR less than 1.5 over this range.
For further details on equipment and antenna installation, see IMOCOMSAR/Circ. 32,
GUIDELINES FOR THE HARMONIZATION OF GMDSS REQUIREMENTS FOR RADIO
INSTALLATIONS ON BOARD SOLAS SHIPS.
2.4.1 Cable requirements
Connect the antennas using a low loss type 50 Ohm coaxial cable, e.g. good quality
RG214 or better. IMO-COMSAR/Circ. 32 recommends the use of a double screened type
cable (like e.g. RG214) with a maximum insertion loss of 3dB across the antenna cable
installation.
The maximum antenna cable length in the installation depends on the quality of the
cable, i.e. the specified attenuation (dB/m) of the cable of choice at the high end of the
VHF frequency band. As a rule of thumb the cable length using e.g. RG214 coaxial
cable should not exceed 25 m.
2.4.2 VHF RX/TX antenna
In installations with two or more VHF radios it is important to ensure the optimum
performance of these by carefully selecting the antenna positions for both radios. It is
recommended to maximize the RF attenuation between the VHF RX/TX antennas in the
installation. You can ensure this by not having the RX/TX antennas positioned at the
same horizontal level, i.e. the RX/TX antennas for each radio must be installed at
shifted elevations as shown in the following drawing.
If sufficient vertical distance between two or more such antennas cannot be achieved,
the horizontal distance between them is increasingly important for optimum
performance. If there is hardly any vertical separation ensure that there is a minimum
of 5 m horizontal distance between any RX/TX antennas in the installation.
To minimize any increase in VSWR of the VHF RX/TX antenna, install the antenna at a
vertical distance of at least 2 m to any other mast, pole or other RF antennas. Keep VHF
antennas as far away as possible from antenna main beam of any radar and satellite
equipment.