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Chapter 3
Communication Ports
Total Gain at PTP GPS Input (includes antenna gain, cable
loss, lightning arrestor loss, line amplifier gain and filter loss)
Section 3.8.3.2
Antenna Cabling
Cable Impedance: Siemens recommends low loss 50 Ω coaxial cabling.
Cable Delay: 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. Siemens provides a method to account for this delay through the
web management interface by entering the time delay into the cable compensation box under PTP General
Configuration. The table below gives some examples of the delay that can be expected based on the dielectric
type.
Dielectric Type
Solid Polyethylene (PE)
Foam Polyethylene (FE)
Foam Polystyrene (FS)
Air Space Polyethylene (ASP)
Solid Teflon (ST)
Air Space Teflon (AST)
Section 3.8.3.3
Lightning Considerations
Although it is not possible to protect the antenna from a direct lighting strike, the antenna and connected
components can be protected from secondary affects through installation location and protection devices.
Install the antenna at least 15 meters 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. Siemens also recommends installing lightning arrestors in the
antenna line to protect the receiver and connected devices. If a lightning arrestor is installed it is important to
ensure that it has a low impedance path to ground.
Section 3.8.3.4
Line Amplification and Filtering
Although an active antenna has gain, depending on the length of the coaxial cable used it may not be enough in
which case a line amplifier will be required as well.
26
Characteristic
Axial Ratio
Output VSWR
Time Delay(ns/ft)
1.54
1.27
1.12
1.15-1.21
1.46
1.13-1.20
RUGGEDCOM RX1100
Installation Guide
Active Antenna
Total Gain ≤ 18 dBi
< 3 dB
< 2.5
PropagationVelocity(% of c)
65.9
80.0
91.0
84-88
69.4
85-90
Antenna Cabling
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