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Installing the Device
2.5.4 Connecting a GPS Antenna
Note
A site survey is recommended prior to any installation to help determine the best
location for the GPS antenna. For assistance, contact a Siemens Sales representative.
Note
Although it is impossible to protect the antenna from a direct lightning strike, the
antenna and connected components can be protected from secondary effects
through site selection and by installing protection devices.
Install the antenna at least 15 m (49 ft) away from and lower than any structures
that attract lightning. GPS antenna damage is usually not the result of a direct
lightning strike, but due to high currents induced by the effects of a lightning strike
on a nearby structure. Lightning arrestors should also be installed in the antenna line
to protect the receiver and connected devices. If a lightning arrestor is installed, it is
important to make sure it has a low impedance path to ground.
To promote signal reception and avoid signal saturation at the receiver input, the
overall GPS system requires a relative gain between 5 and 18 dBi.
Use only low loss, 50 Ω coaxial cabling when connecting the GPS and any other
optional components to the RUGGEDCOM RX1400.
Note
Using any length of coaxial cable will add some time delay to the GPS signal,
which degrades the accuracy of the calculated time and position. The time delay is
dependent on the type of dielectric material in the cable and ranges from 1 to 2 ns/ft.
The table below gives some examples of the delay that can be expected based on the
dielectric type.
Air Space Polyethylene (ASP)
To connect a GPS antenna, do the following:
1.
22
Dielectric Type
Solid Polyethylene (PE)
Foam Polyethylene (FE)
Foam Polystyrene (FS)
Solid Teflon (ST)
Air Space Teflon (AST)
Mount the antenna to a pole or wall in an area that provides good signal
coverage and is away from any signal noise emanating from other
communications equipment. Make sure 90° of the sky is visible to the antenna.
Time Delay (ns/ft)
1.54
1.27
1.12
1.15 to 1.21
1.46
1.13 to 1.20
Installation Manual, 01/2021, C79000-G8976-1103-17
Propagation Velocity (% of c)
65.9
80.0
91.0
84 to 88
69.4
85 to 90
RUGGEDCOM RX1400
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