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11...A mast of some sort used to augment the existing roof height of the vehicles does provide a very significant increase in the
performance of these devices. The operationally easiest of these masts is the pneumatic, pump-up, variety although there are
others. A suggestion is that where possible, the aerial is permanently fitted to the top of the mast as this makes life very much
simpler when trying to find a suitable location to park the vehicle when it’s in use. A test transmission can be made from the vehi-
cle using the rebroadcast system without needing to extend the mast. Indeed, if adequate comms exist using the rebro without
the mast extended, then don’t bother extending it. The whip aerials we all use on our vehicles come in a form that allows them to
be fitted to the top of a mast. These are called ‘Ground-Plane’ aerials and usually have a standard vertical whip section and a set
of three horizontal helicals that substitute for the missing ground plane, usually the metal roof of the vehicle.
Left is a standard ground plane aerial manufactured by Panorama and
is only slightly higher than the normal vehicle mounted whips. It’s per-
formance is good and it can be left mounted on the collapsed mast
when the vehicle is returned to base. If you are lucky enough to be
able to drive it into the garage then it can be left fitted permanently.
If you choose this option then it’s a very good idea to use a proprietary
thread fixing agent, Locktite or similar, on the helicals as this will help
to keep them in place. Operating this type of aerial without the ground
plane elements isn’t recommended!
The supplied nylon wing-nuts need backing up with locking nuts for
safety.
The BNC is probably the worst type of RF connector you could wish for
on a system that is subject to movement and vibration. Eventually the
central pin will splay out the contacts it sits in and the assembly will be-
come electrically noisy. There’s nothing you can do about this apart
from securely binding the connections in place with self-amalgamating
tape or similar. BNC connectors are NOT water-proof!
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