Tait TB7300, Инструкция по установке и эксплуатации

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64 Installation TB7300 Installation and Operation Manual
© Tait Limited November 2016
5.6.3 Connecting RF
Notice Do not remove the load from the base station while it is trans-
mitting as this may damage the PA output stage. Before disconnecting
any RF cables, put the base station into Offline mode to prevent any
transmissions.
The RF input to the base station is via the marked BNC connector on the
rear panel. The RF output is via the N-type connector on the rear panel
(refer to
Figure 5.4 on page 62 ).
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.
Recommendations
for Installing the
Base Station
We recommend the following installation procedures, which should protect
the PA from damage under all but the most extreme operating conditions.
1. Do not connect the base station directly to the antenna. Fit an isolator
or duplexer between the base station and the load. Fit the isolator as
close as possible to the RF output connector on the base station. Do
not connect any switching equipment between the isolator and the
base station, unless the switch
cannot operate while there is RF pres-
ent (i.e. the base station is transmitting).
2. Fit a surge suppressor to the antenna cabling where it enters the
building.
3. Inspect all cables and equipment connected to the base station for
defects.
Ice on the antenna, or a broken antenna, is unlikely to cause damage to the
PA.
Explanation
The circuit design of the PA protects the circuitry from high VSWR. This
makes it difficult to damage the RF power device by keying the PA into a
mismatched load, or if the load deteriorates over even a short period of time
(milliseconds).
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.