70 Installation TB9100/P25 CG/P25 TAG Installation and Operation Manual© Tait Limited March 2014However, it is possible to damage the device if all the following conditionshappen at the same time:■ there is a step change in the PA load (for example, the load is removed)■ the PA is transmitting■ the feed line loss between the PA and the mismatch is <1dB.The effect of such conditions is variable: some devices will not be destroyed,and some may fail after repeated load interruptions.Connecting an External Frequency ReferenceFor K4 Band, the internal frequency reference accuracy is inadequate, andan external reference must be used. An external reference is also requiredfor simulcast. The external reference frequency can be 10MHz or12.8MHz, with an input level of 300mVpp to 5V pp. The stability of thisreference should be better than 50 parts per billion (for non-simulcast) or≤1 part per billion (for simulcast).If an external reference is required, use the CSS to program the base stationfor 10MHz or 12.8MHz (“Configure > Network Element >Miscellaneous”), and to enable the external reference “Absent” and“Invalid” alarms (“Configure > Alarms > Control”).Use a 50Ω coaxial cable (RG58 or RG223) to connect the externalreference to the base station’s external reference frequency input. You candaisy-chain up to eight base stations using T-junctions. The maximumoverall cable length is 30m. Terminate the last connection with a 50Ω load.
