Paradise Datacom P300-VSAT Installation & Operating Handbook page 211

Text on Display
Rx Warn: Back' alm 1234 from satellite
Rx Warn: O/p clk fail=<source>, now PLL
Rx Warn: No clk ref=<source> , now int'
Rx Warn: Back' alm received at ins' mux
P300H
Description / Cause / Notes
The display may show numbers or dashes (eg "-2-4") corresponding to which of the four backward
alarms are active at the Rx Input. This indicates that equipment downstream of the TRANSMIT
path (ie the distant end Rx path or further downstream) has failed and is returning an alarm. In
Multidestinational circuits this may NOT correspond to the Tx path of THIS MODEM. The fault may
be due to any receive downstream equipment, but could be due to the relevant modem Tx output
failing. Check the relevant modem Tx path indicates OK, Check the Tx IF output from the modem
is connected to the upconverter equipment and onwards, monitor the Tx carrier (or distant Rx if
possible) with a spectrum analyser.
The clock selected as the Receive data output clock, (where <Source> shows the specified clock)
has failed. The modem has switched to using a backup clock generated by the Rx PLL to preserve
the receive traffic. This fault only occurs if the <source> is the same frequency as the Rx data rate,
otherwise the clock is not used directly instead it is rate converted by the Rx PLL, and it's failure
results in the fault described immediately below instead. Refer also to the description of the
dialogue under (Change, Rx, Buff/Clk, Rx Clock) to determine which signal the PLL uses as a
backup clock.
The reference specified for the PLL which generates the Rx output clock (or backup Rx clock) has
failed, the modem has switched to using the internal 1PPM reference to keep the clock available.
Check the clock <source> specified is present. If a station clock is specified as available the
modem will use this as the <source> to generate the backup Rx output clock even if "Station" not
specified as the primary source on the Rx Clock Mode screens. Check that the Station clock is still
connected as it is a common mistake to change the Rx Clock Mode to something other than
"Station", then disconnect the station clock assuming the modem will not use it, whereas the
modem will always use it in preference to the internal 1PPM clock if it is has been told a station
clock is available. (Change, Rx, Clock/Buff, Station Clock Input).
This fault will only be displayed if the modem if fitted with an interface which provides four ports for
separate input and output of separate Tx/Drop and Rx/Insert PCM bearers. It indicates a Backward
Alarm is detected at the Rx bearer Input. This indicates that equipment downstream of the
RECEIVE path has failed and is returning an alarm. This may be due to any receive downstream
equipment, but could be due to the modem Rx output failing. Check the modem Rx path indicates
OK, Check the Rx data output from the modem is connected to the downstream equipment.
P300 Series Installation and Operating Handbook
Relays To Terr To Sat Other
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