Communication Ports
RuggedCom
®
- Rev.122
36
RuggedRouter
®
RX1000 Family
4.10.2.1 GPS Antenna
There are two major types of GPS antenna: passive and active. A passive antenna
requires no power and is an option when signal strength is not a concern. An active
antenna has a built in Low Noise Amplifier (LNA) to increase the strength of the
signal, and to compensate for the signal loss in a long cable connection. Active
antennas are used when the antenna input is connected to the receiver through a
coaxial cable (usually longer than 3 m) or any high loss transmission path.
The PTP Card requires an active antenna with the following specifications:
Characteristic
Active Antenna
Polarization
Right-Hand Circular Polarized
Receive Frequency
1.57542 GHz ± 1.023 MHz
Power Supply
5 VDC
DC Current
< 10 mA at 3 VDC
Antenna Gain
Select antenna gain based on system
configuration
Total Gain at PTP GPS Input (includes
antenna gain, cable loss, lightning
arrestor loss, line amplifier gain and filter
loss)
Total Gain
≤ 18 dBi
Axial Ratio
< 3 dB
Output VSWR
< 2.5
Table 12: GPS Antenna Specifications
NOTES:
The PTP card‟s GPS input provides 5 VDC at up to 10 mA to power the
antenna.
Best results can be achieved with a total gain of 16 dB (includes antenna
gain, cable loss, lightning arrestor loss, line amplifier gain and filter loss) at
the antenna input.
4.10.2.2 Antenna Cabling
Cable Impedance:
RuggedCom 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.
RuggedCom 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.
