INSTALLATION
MOBILE STATIONS
ENVOY™ TRANSCEIVER REFERENCE MANUAL 397
As the fuse is not included to protect the transceiver circuits, it should be of large
physical and electrical size to eliminate the possibility of voltage drops across the
fuse.
WARNING: Do not use normal glass in-line automotive fuses.
Earthing the transceiver in a mobile station
A good RF earth is essential for efficient operation of the mobile station. The
transceiver chassis should be connected to earth via the earth screw on the rear panel
of the transceiver. Use a copper braid of at least 12 mm (½ in) width to connect the
transceiver to the earthing point.
NOTE: Keep the earth braid as short as possible.
All individual units in a mobile station should be earthed to prevent RF interference
corrupting the data and audio circuits. Equipment that requires earthing has an earth
screw fitted. To achieve good earthing, connect separate earth braids to the earth
screws on each piece of equipment and connect them back to the same earthing point.
An adequate earthing system is necessary for:
• static drain
• noise reduction
Related links:
Static drain on page 397
Noise reduction on page 397
Static drain
In some cases, wind-driven particles, such as dry sand, may charge the transceiver and
ancillaries to very high voltages above earth. Usually the low-impedance protective
earth connection prevents high voltages from building up. In the event that the
protective earth is disconnected or does not exist, as for a solar-powered fixed
installation, these high voltages may occur.
If the voltage of the electrostatic charge becomes sufficiently high, a flashover could
occur between the charged parts and earth. The energy released at flashover depends
upon the voltage of the charged parts to earth. This energy generates a steep wave
front, which may cause failure in the front end of the transceiver or result in damage
elsewhere.
Noise reduction
In some cases, noise can be reduced by connecting the case of the transceiver directly
to earth. If an improvement is noticed, the existing functional RF earth may be
inadequate and need improvement.
Where the antenna and transceiver must be installed in close proximity, directly
earthing the transceiver may be necessary to eliminate RF feedback.
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