Motorola DIMETRA MTS 2, Installation, Configuration And Basic Service Manual

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GPS Antenna Line Loss Chapter 4: Hardware Installation
Figure 4-50 GPS Antenna Connection on MTS 4 Junction Panel
GPS Antenna Line Loss
The maximum allowable line attenuation between the antenna and the Site Controller GPS
Receiver input is 6 dB. There is an additional 4 dB of attenuation for foliage. In a typical MTS
installation using 1/2 inch low density foam coaxial cable (or equivalent), the length of the cable
run should never exceed 46 m. This is suf
fi
cient for most installations.
When considering the use of longer cables, calculate the cable lengths allowing 4.5 dB
of loss at 1.5 GHz (the GPS receiver frequency). The remaining 1.5 dB of attenuation
is provided by interior site cabling and connectors.
Avoiding GPS Interference
High frequency radio waves, such as those broadcast by the GPS system behave like light (straight
lines) therefore it is likely that any long term interference will be ground based. Two strategies
have been successfully employed to mitigate against jamming signals:
•
If possible, determine a location where adequate GPS signals are available using a hand
held receiver and move the Base station GPS antenna to this location.
•
Construct a shield (Cardboard & Foil is adequate) to exclude the jamming signal. The shield
should be approximately 6 cm from the antenna body and should be connected to an earth point.
4-52
6802800U74-N September 2009