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TB9400 Installation and Operation Manual
Installation
89
© Tait Limited March 2015
5.5
Installing the Base Station on Site
5.5.1
Base Stations for Trunked Systems
When installing base stations that are part of a trunked system, it is very
important to observe good site engineering rules. This is especially true
when the channels are combined into a single antenna.
important to observe good site engineering rules. This is especially true
when the channels are combined into a single antenna.
If at all possible, the RF planner should avoid frequency plans in which the
Rx to Tx spacing is an exact multiple of the trunked channel spacing, thus
forcing Tx intermodulation products to fall outside the Rx channels.
Rx to Tx spacing is an exact multiple of the trunked channel spacing, thus
forcing Tx intermodulation products to fall outside the Rx channels.
Cables and antennas should be of high quality construction. Solid shield
heliax type cables are best, but if braided shield cables must be used for
short distances, their braids must be silver-plated.
heliax type cables are best, but if braided shield cables must be used for
short distances, their braids must be silver-plated.
When the outputs of more than one transmitter are combined, their voltages
add, and the resulting peak envelope power is not simply the sum of their
powers, but is equal to the power of one of them multiplied by the square
of the number of sources. Cables, components, and hardware must be rated
to withstand the peak envelope power.
add, and the resulting peak envelope power is not simply the sum of their
powers, but is equal to the power of one of them multiplied by the square
of the number of sources. Cables, components, and hardware must be rated
to withstand the peak envelope power.
During the commissioning process, all transmitters should be activated
together using a diagnostic test tone, while the receiver RSSI is monitored.
There should be no perceptible increase in RSSI while the transmitters are
active.
together using a diagnostic test tone, while the receiver RSSI is monitored.
There should be no perceptible increase in RSSI while the transmitters are
active.
Base stations may require an external frequency reference, a 1PPS signal,
and an NTP source, depending on the frequency band and type of radio
system.
and an NTP source, depending on the frequency band and type of radio
system.
The following general rules apply:
■
Base stations operating at or above 700MHz require an external
frequency reference to meet the frequency accuracy requirements for
transmitters and receivers.
frequency reference to meet the frequency accuracy requirements for
transmitters and receivers.
■
Simulcast transmitters require an external frequency reference and a
1PPS signal so that transmissions can be timed with the required
accuracy. They also require an NTP source that is derived from the same
source as the 1PPS signal. This will ensure a common timestamp in logs
across all units in the system
1PPS signal so that transmissions can be timed with the required
accuracy. They also require an NTP source that is derived from the same
source as the 1PPS signal. This will ensure a common timestamp in logs
across all units in the system
■
P25 Phase 2 base stations require an external frequency reference and a
1PPS signal for site alignment of transmitters and receivers. They also
require an NTP source to ensure correct, long-term Phase 2 alignment.
1PPS signal for site alignment of transmitters and receivers. They also
require an NTP source to ensure correct, long-term Phase 2 alignment.
The requirements for P25 Phase 1 systems are described in more detail
below. Also see
below. Also see
and