then different antennas must be used. It is recommended to mount the antennas at least
30 cm from any edge where possible.
For dual antenna systems, the secondary antenna should be mounted in the same
orientation as the primary antenna, as shown in Figure 2. The antenna baseline should
also be aligned with one of the vehicle axes where possible, either inline or perpendicular
to the vehicle’s forward axis. In the default configuration the primary antenna should be
at the front of the vehicle and the secondary antenna should be at the rear.
Figure 2. Dual antenna orientations
A)
The bases of the antennas are parallel, but the cables exit in different directions. B) The cables
exit in the same direction but the bases of the antennas are not parallel. C) The bases of the antennas are
parallel and the cables exit in the same direction. This configuration will achieve the best results.
It is best to mount the two antennas on the top of the vehicle. Although it is possible to
mount one on the roof and one on the bonnet (hood), the multipath reflections from the
windscreen will degrade the performance of the system.
Multipath affects dual antenna systems on stationary vehicles more than moving vehicles
and it can lead to heading errors of more than 0.5° RMS if the antennas are mounted
poorly.
It is critical to have the RT mounted securely in the vehicle. If the angle of the RT can
change relative to the vehicle, then the dual antenna system will not work correctly. This
is far more critical for dual antenna systems than for single antenna systems. The user
should aim to have no more than 0.05° of mounting angle change throughout the testing.
(If the RT is shock mounted then the RT mounting will change by more than 0.05°; this
is acceptable, but the hysteresis of the mounting may not exceed 0.05°.)
For both single and dual antenna systems it is essential that the supplied GNSS antenna
cables are used and not extended, shortened or replaced. This is even more critical for
dual antenna systems and the two antenna cables must be of the same specification. Do
not, for example, use a 5 m antenna cable for one antenna and a 15 m antenna cable for
the other. Do not extend the cable, even using special GNSS signal repeaters that are
designed to accurately repeat the GNSS signal. Cable length options are available in 5 m
and 15 m lengths.
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