Tait TB9400 Installation And Operation Manual

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Tait TB9400 Installation And Operation Manual Manual pdf 65 page image

TB9400 Installation and Operation Manual Installation 65© Tait Limited March 20174.5 Installing the Base Station on Site4.5.1 General Installation AdviceWhen installing base stations, it is very important to observe good siteengineering rules. This is especially true when the channels are combinedinto a single antenna.If at all possible, the RF planner should avoid frequency plans in which theRx to Tx spacing is an exact multiple of the trunked channel spacing, thusforcing Tx intermodulation products to fall outside the Rx channels.Cables and antennas should be of high quality construction. Solid shieldheliax type cables are best, but if braided shield cables must be used forshort distances, their braids must be silver-plated.When the outputs of more than one transmitter are combined, their voltagesadd, and the resulting peak envelope power is not simply the sum of theirpowers, but is equal to the power of one of them multiplied by the squareof the number of sources. Cables, components, and hardware must be ratedto withstand the peak envelope power.During the commissioning process, all transmitters should be activatedtogether using a diagnostic test tone, while the receiver RSSI is monitored.There should be no perceptible increase in RSSI while the transmitters areactive.Base stations may require an external frequency reference, a 1PPS signal,and an NTP source, depending on the frequency band and type of radiosystem.The following general rules apply:■ Base stations operating at or above 700MHz require an externalfrequency reference to meet the frequency accuracy requirements fortransmitters and receivers.■ Simulcast transmitters require an external frequency reference and a1PPS signal so that transmissions can be timed with the requiredaccuracy. They also require an NTP source. Both the 1PPS and NTPsignals must be derived from a source that is GPS-disciplined. This willensure a common timestamp in logs across all units in the system.■ P25 Phase 2 base stations require an external frequency reference and a1PPS signal for site alignment of transmitters and receivers. They alsorequire an NTP source to ensure correct, long-term Phase 2 alignment.The requirements for P25 Phase 1 systems are described in more detailbelow. Also see “Connecting an External Frequency Reference” onpage 76 and “Connecting a 1PPS Source” on page 77.