68P80801E30-A 5/1/2002 3-21
Gen 3 Site Controller System Manual Chapter 3 Pre-Installation
Antenna Installation
GPS antennas are color coded yellow. The same identification technique
used for RF antennas is also used to identify the GPS antennas, refer to
Table 3-4. Antenna 1 should always be the northern-most antenna.
GPS Antenna Line Loss
The maximum allowable line attenuation between the antenna and the GPS
receiver is 6 dB. In addition, there is a 4 dB foliage margin. Installations in
which the antenna has an unobstructed view of the sky may have a
maximum line attenuation of 10 dB. In a typical installation using 1/2” low
density foam coaxial cable, the length of the cable run should never exceed
150’. This is sufficient for most installations.
When considering the use of larger cables, calculate the cable lengths
allowing a maximum allowable line attenuation of 4.5 dB at 1.5 GHz. The
remaining 1.5 dB of attenuation is provided by interior site cabling and
connectors.
Another option is the use of in-line amplifiers to overcome excessive line
loss. The in-line amplifiers are powered by the 5 Vdc supplied by the GPS
receiver and are inserted somewhere between the GPS antenna and the site
controller, preferably near the antenna. Either the connector on the coaxial
line must be changed to fit the amplifiers, or a short jumper cable must be
field fabricated.
Table 3-4 GPS antenna identification
Band Description
one yellow band GPS antenna 1 (northern-most)
two yellow bands GPS antenna 2
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