Antenna; Transmission Range - mcmurdo R2 GMDSS Owner's Manual

3.2 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 overloading of the power mod-
ule. Damaged antennae should be replaced immediately.
Replacement antennae can be purchased from authorised McMurdo Service Agents. Please refer to sec-
tion 3.7 for more details on spare parts and accessories available.

3.3 Transmission Range

Because VHF signals travel in a straight line and are not reflected back off the ionosphere as lower fre-
quency signals are, the range of VHF signals is limited to 'line of sight', beyond which the other vessel pass-
es behind the curve of the Earth. Therefore, the range will increase greatly the higher above sea level the
antenna is, as Fig 3.1 illustrates (assuming maximum transmission power is used):
Cherbourg
30 m/
100 ft
Mast
Endeavour
Therefore, 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).
87 km / 65 M
20 km / 12 M
9 m/
30 ft
Mast
Fig 3.1 - VHF transmission range
Isle of Wight
Niton
8 km / 5 M
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