User's Manual

Transmit Antenna on the STR 3000 Simulcast Base Radio Rack Chapter 2: Installing the Simulcast Subsystem Hardware
Transmit Antenna on the STR 3000 Simulcast Base Radio Rack
One transmit cavity combiner can support up to 12 base radios per transmit antenna. It is possible to
combine the base radios into as few as two cabinets, if they are adjacent. To increase system reliability
and eliminate a single point of failure, use a minimum of two transmit antennas per site.
GPS Requirements
A simulcast subsystem uses two Global Positioning System (GPS) antennas to provide a certain degree
of redundancy in case one antenna is damaged or inadvertently shadowing. Mount the two antennas at
least 3.05 m (10 ft.) apart with an unrestricted aerial view down to within 10˚ of the horizon in all
directions. The antennas must also be mounted high enough to clear the peak of the site roof.
Defining the Correct View for the Location
The hemispheric location of the site also affects installation of the GPS antennas. For systems in the
northern hemisphere, mount the antennas to maintain a clear view of the southern sky. For systems in
the southern hemisphere, mount the antennas to maintain a clear view of the northern sky.
Avoiding Obstructions
Be careful to avoid adjacent structures (such as trees and buildings), which can obstruct the GPS
antennas with their wide and solid profiles. Mount the antennas to clear these types of obstructions.
However, an adjacent antenna tower that protrudes into the required view at a prime or remote site does
not obstruct the view and only has a minimal effect on reception from the GPS satellite.
Isolate the GPS antennas from any RF interference by mounting the antennas at least
12˚ horizontally from other transmitting antennas.
GPS Antenna Line Loss
The maximum allowable line attenuation between the antenna and the TRAK 9100 GPS receiver is 10 dB.
This 10 dB figure includes a 4 dB margin for attenuation from foliage. So, in an installation in which there
is interference from foliage, allow for 6 dB line loss and 4 dB foliage attenuation. 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 0.5-in. low density foam coaxial cable, the length of the cable run
should never exceed 45.72 m (150 ft.). This is sufficient for most installations.
When considering the use of larger cables, calculate the cable lengths allowing 4.5 dB of loss at 1.5 GHz.
The remaining 1.5 dB of attenuation is provided by interior site cabling and connectors.
For more information on installation of the GPS antenna, see "Installing the Global
Positioning Satellite Antenna" on page 3-26.
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68P81003Y71-O November 2002