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<h1>TX Antenna VSWR Supervision</h1>

<p>All combiners are capable of monitoring the VSWR (Voltage
Standing Wave Ratio) at the combiner output. This monitoring is a continuous
procedure and fully automatic. Two levels of indications are provided, lower
and upper. The threshold for upper indication is 3.0 and for lower 2.3. With
the RTC, the threshold for the lower indication can be set in range from 1.6
to 3.0. This is not available with wide band combiners. When either of the
level is exceeded, the combiner raises an alarm, and the BCF sends the alarm
to the BSC, which then takes the necessary recovery actions. When the lower
level is exceeded, the alarm is non-fatal, and the service can continue. When
the upper level is exceeded, a fatal alarm is raised.</p>


<p>In Nokia Talk-family of BTSs the monitoring of the antennas
in dual duplex configuration will be organised as follows:</p>


<p>The VSWR of the antenna carrying the BCCH shall be monitored
during normal operation. The other antenna does not have a continuous transmit
signal, which is mandatory for the VSWR measurement.  Therefore, the BCF must
start a continuous fixed level transmission on one of the TRXs connected to
the other antenna. When the measurement is completed, transmission is switched
off. The transmission power used during the test is the BCCH power defined
for this cell.</p>


<p>The above covers the antenna supervision when base band
hopping is not used. When base band hopping is used, it is necessary to activate
transmission in all TRXs belonging to the same hopping group in order to ensure
continuous transmission in the antenna. Otherwise, the procedure is the same.</p>
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