Text on Display
Description / Cause / Notes
Relays
To Terr
To Sat
Other
P300H
P300 Series Installation and Operating Handbook
Page 210
Rx Fault: Clk PLL lock fail to <source>
The PLL which generates the Rx output clock (or backup Rx clock) has failed to lock to the
T
TA,TC
RF
specified reference. Check the reference specified as <source> is the correct frequency. If a
station clock is specified as available the modem will use this 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 to generate the backup clock 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).
RX WARNINGS
(Bottom line of display)
Rx Traffic warnings: Deferred alarm relay only
Rx Warn: Reconfiguring Rx path
The modem is reconfiguring the Rx path (after a user parameter change).
Rx Warn: Backward alarm from satellite
A Backward Alarm is detected at the Rx Input. This indicates that equipment downstream of the
D
TB
TRANSMIT path (ie from our modem Tx output, though the Tx chain, through the satellite and then
through the whole distant end Rx path or even further downstream) has failed and is returning an
alarm. This may be due to a receive downstream equipment failure, this Tx chain failing, the
satellite itself, but also possibly the modem Tx output failing. Check the 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.
Rx Warn: CAS MF Back' alm from sat
A Multiframe Backward Alarm is detected at the Rx Input, this indicates that equipment
D
TE
downstream of the TRANSMIT path has failed to find CAS Multiframe sync and is returning an
Note 7
alarm. Realistically while this could be caused by any equipment from the Tx modulator onwards, it
is unlikely to be other than the Tx mod, the Rx demod, or further down the Rx path as other failures
would result in a more catastrophic failure (and the correspondingly more significant backward
Alarm above). The Modem only detects this alarm when the Rx baseband is set to use the Insert
mux in a G.732 mode and CAS signalling has been selected (or 2048k IBS G.732 0% overhead
mode with CAS is enabled). Read the text corresponding to “Rx Fault: CAS Multiframe sync lost” to
determine why a CAS multiframe is in use over satellite and Check the three items listed against
this message on the Tx path of this modem.