BRUEL & KJAER PULSE 7788, Technical Documentation Manual

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PULSE Vehicle Pass ‐ by Test Systems – Installation Manual 36
The higher the gain, the more directional the antenna. We commonly use
omnidirectional antenna, which have a broadcast pattern like a disk when viewed from
above and like a symmetrical horizontal ellipse when viewed from the side. The gain is
expressed in dBi and is a comparison of the signal intensity measured in the position of
maximum gain using a reference of the signal intensity of an isotropic radiator, that is,
an antenna that gives a uniform spherical broadcast pattern. We commonly use 13 dBi
diversity antenna for the Ground Station and 6 dBi magnetic mounted antenna for the
Vehicle Station.
Consideration must be taken of the maximum broadcast signal strength allowed in the
region where the system is operated. You can adjust the broadcast strength as part of the
WLAN hardware configuration.
Reflections from Chainlink Fences
This is a special problem encountered quite regularly. Chainlink fences appear to be
efficient reflectors of WLAN signals, creating interference and loss of performance.
Boosting signal output by using different hardware does not solve the problem, as the
strength of the reflections also increases. Strategies for dealing with chainlink fences
include the use of directional antenna that avoid broadcasting at the fence, mounting
the antenna on top of the fence itself, or mounting the Ground Station antenna higher
so that it broadcasts over the fence.
Radio Pollution
The rapid rise in popularity of WLAN solutions means that you are generally sharing
bandwidth if you are in any populated area. Sharing the frequency band with another
WLAN unit broadcasting on the same channel and transferring data, will reduce your
throughput and the broadcast range will suffer. Therefore, it is important that you do a
wireless site survey to see what other networks are sharing your bandwidth and to
choose an operating channel as far away for other networks as possible.