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70 Installation TB9100/P25 CG/P25 TAG Installation and Operation Manual

However, it is possible to damage the device if all the following conditions

happen 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 Reference

For K4 Band, the internal frequency reference accuracy is inadequate, and

an external reference must be used. An external reference is also required

for simulcast. The external reference frequency can be 10MHz or

12.8MHz, with an input level of 300mV

to 5V

. The stability of this

reference 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 station

for 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 external

reference to the base station’s external reference frequency input. You can

daisy-chain up to eight base stations using T-junctions. The maximum

overall cable length is 30m. Terminate the last connection with a 50Ω load.

Tait TB9100 User Manual

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