Ng Analysis - Nera Inmarsat-c Service Manual

5.3.2 NG analysis

BBER
When the receiving error rate of the bulletin board which is on the top of TDM channel
is over 80%, the message, "WARNING: BBER over 80%. SCANNING NCS start
manually" appears. Check the RX circuit on RF CON/CPU board.
C/N
"NG" appears when the RX signal is weak. The BPSK modulated I signal and Q signal
at RF CON/CPU board is input to U14 (CPU) to output C/N data. When the C/N level
of the RX signal is more than 31dB, "OK" appears. The followings are the parts which
the error may be occurred;
- Antenna unit
- Antenna coaxial cable
- Coaxial connector
- RX circuit on the RF CON/CPU board
- Antenna blocking
Send Level
The send level detects the current supplied to the antenna unit and displays as the send
level. PWR board detects the send level. Normally, the value is fixed to "0" when
receiving and "255" when sending.
**When the log-in;
When the receiving is normal, the error occurred at the transmission part of the
antenna unit or RF CON/CPU board, results in the login failure, and then following
message appears.
- Too many retries.
- MES Signalling Failure, Login Request not sent to NCS.
- Login failed.
The followings are the parts which the error may be occurred;
- Antenna unit
- RF CON/CPU board
- PWR board
Antenna Power Supply
It is detected from the voltage, TX 29 V/RX 7 V supplied to the antenna unit. This
voltage is divided at R97, R98 and R99 on the PWR board, and the Check V signal is
sent to RF CON/CPU board. When the voltage is out of the ratings for transmitting and
receiving, "NG" appears. The followings are the parts which the error may be occurred;
- Antenna coaxial cable
- Antenna unit
- PWR board
5-11
5.3 Status monitor