TB9400 Installation and Operation Manual
Installation
81
© Tait International Limited November 2019
4.6.5
Connecting RF
Notice
Do not remove the load from the PA while it is transmitting
as this may damage the PA output stage. Before disconnecting any RF
cables, put the base station into Offline mode to prevent any transmis-
sions.
The RF input to the base station is via the marked BNC connector on the
rear panel of the reciter. The RF output is via the N-type connector on the
rear panel of the PA (refer to
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 PA
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 PA directly to the antenna. Fit an isolator or
duplexer between the PA and the load. Fit the isolator as close as pos-
sible to the RF output connector on the PA. Do not connect any
switching equipment between the isolator and the PA, unless the
switch
cannot
operate while there is RF present (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.
