3-3
Antenna Considerations (Skymap IIIC only)
When positioning the antenna, always ensure that the domed (the opposite side to that which
carries the CE marking) face of the antenna is facing straight up to the sky and can “see” a
large area of the sky, preferably right down to the horizon. In order to provide a 3-dimensional fix,
Skymap IIIC needs to receive signals simultaneously from at least four satellites.
The radio signals from the GPS Navstar satellites are transmitted in an extremely high frequency band
(1.5GHz). They can be regarded as having approximately the same penetration capabilities as light.
This means that they are able to penetrate only transparent or very thin materials and will be blocked
by almost any material that blocks light.
At least four and at times up to eight GPS satellites should always be in view from any place in the
world at any time. These can, however, be absolutely anywhere in the sky and so, to ensure
uninterrupted navigation it is essential that the antenna has direct line-of-sight contact with as much
sky as possible.
If the position in which you wish to locate your Skymap IIIC is shielded from the sky and the standard
antenna cable is not long enough for an acceptable installation bearing the above guidelines in mind,
you may choose one of several options for remote antenna sitting. The simplest is to use the
Bendix/King remote antenna extension cable. This allows the portable antenna to be extended by a
further 6ft (2 metres) thereby allowing mounting up to 12ft (4 meters) away from the main unit. The
antenna may be held in place there by using the rubber suction cup supplied (which should be slotted
into the key hole in the antenna bracket) or fixed permanently in position by using the countersunk
screw mounting holes in the antenna bracket. The rubber suction cup is ideal for temporary use in
vehicles and light aircraft. The portable antenna is only splash proof and not fully waterproof. Never
mount this antenna permanently outside.
For permanent external antenna mounting an external magnetic mount antenna is available for ground
vehicles and an external low profile "tear drop" style antenna for aircraft. For more information about
these accessories please contact your Bendix/King dealer.
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