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Installation
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9.4.2 RX/TX antenna
In installations consisting of two or more VHF radios it is important to ensure the optimum
performance of these by carefully selecting the mutual antenna positions.
In general the highest possible RF attenuation between the VHF RX/TX antennas in the
installation should be sought for. The most important parameter in achieving this is by
ensuring that none of the RX/TX antennas in the installation are positioned at the same
horizontal level, i.e. the RX/TX antennas must be installed at shifted elevations as indicated
below.
In situations where sufficient vertical distance between two or more such antennas is found
difficult to obtain the horizontal distance between them will play an increasingly important
role in the equipment performance the less the vertical separation and as a minimum 5m
horizontal distance between any RX/TX antennas in the installation should be ensured.
Additionally, in order to minimize any increase in VSWR exhibited by the VHF RX/TX
antenna this should be installed in a distance no closer to any other mast/pole object or other
RF antennas than which corresponds to the physical length of the antenna itself, i.e. an
antenna of e.g. 1.2m length should be installed no closer than 1.2m to any other superstruc-
ture object or RF antenna.
To the widest possible extend the VHF antennas should be kept out of the antenna main
beam of any radar and satellite equipment.
9.4.3 DSC antenna
The positioning of the DSC antennas is less critical in terms of the imposed VSWR and due
to the nature of the DSC-signalling. It should be noted however, that the DSC receiver of a
VHF is likely to be temporarily blocked in reception due to high signal blocking, if the
associated DSC antenna is installed in close vicinity of a RX/TX antenna at the same
horizontal level while transmission takes place from this RX/TX antenna.
RX/TX
DSC
RX/TX
DSC
No. 1 VHFNo. 2 VHF
No. 2 VHFNo. 1 VHF
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Example of VHF antenna arrangement.
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