TETRA Antenna Combiner
Radio Systems Information Ltd.
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Maintenance
The Antenna Combiner should be fully re-calibrated every 12 months.
It is recommended that every 3 months – or more often if the Combiner has been used in a
vehicle a lot – that the top cover should be removed and all RF connectors should be carefully
tightened by hand (do NOT use a tool to over-tighten the connectors).
It is recommended that the following functional checks are made every week:
1) With the combiner installed in a survey vehicle and connected to the Gemini survey tool,
park the survey vehicle in an open area away from any buildings and at least 250m from
any TETRA base transmitters.
2) Put each TETRA radio into engineering mode so that the RSSI is displayed.
3) Connect the survey antenna direct to the TETRA radio antenna. Make a note of the RSSI
and the serving base LAC
4) Connect the survey antenna to the Combiner antenna port, connect the TETRA radio to
the relevant port connector and make a note of the RSSI, ensuring that the serving base
LAC is the same as before.
5) Confirm that the difference between the two RSSI measurements is /- 2dB of the
expected loss for each port.
Note that the above functional test can produce misleading results if the survey antenna is not
correctly tuned (i.e. it is not a good 50ohm impedance).
