Technical data

HT50/HT51/HT53 & Axis 50 GMDSS
16
E03766 Issue 3.0
3.3 Antenna
The antenna for the radio is fitted to the unit via a robust screw
fitting to an M6 threaded socket on the top of the radio. This
system is more rugged than a traditional BNC connector, so the
radio’s drop-proof integrity is not compromised by the antenna
fixing. While the radio is drop-proof and very robust, damage
to the antenna such as bending or kinking may adversely affect
the transmission efficiency of the unit, which may lead to over-
loading of the power module. Damaged antennas should be
replaced immediately.
➞ Replacement antennas can be obtained from authorized
Simrad agents. For further details see sections 3.8 and 3.11.
3.4 Transmission range
Because VHF signals travel in a straight line and are not
reflected back off the ionosphere as lower frequency signals are,
the range of VHF signals is limited to ‘line of sight’, beyond
which the other vessel passes behind the curve of the Earth.
Therefore, the range will increase greatly the higher above sea
level the antenna is positioned, as Fig 3.1 illustrates (assuming
maximum transmission power is used):
The typical range of a handheld radio such as this one used at
sea level will be approximately 8 km (5 miles). This will increase
as height above sea level increases, or if the other radio user’s
antenna is at a greater height – note that the range between the
yacht with the antenna mounted on a 9 m (30 ft) mast and the
handheld user increases to 13–16 km (8–10 miles).
Fig 3.1 - VHF transmission ranges