IBUC Operation Manual
Terrasat Communications, Inc.
Rev. A
7-33
To ensure uninterrupted service a line conditioner and/or UPS is recommended based
on the expected AC power at the site.
Site Related Problems
VSAT antennas are often fitted on top of buildings. Avoid close proximity to elevator
motors, etc. Also ensure that the satellite signal path is free and clear of obstructions.
M&C Checks
When troubleshooting the Redundant Systems the first level of troubleshooting should
be to check the status through the M&C ports. Alarms and an alarm history are
available. Refer to later in this chapter for specific information when using the RS232,
RS485, Ethernet or Handheld Terminal ports.
Power Supply Checks
Before starting the RF troubleshooting first verify that the proper voltages are being
supplied to the Tx and Rx Redundant Systems. Input DC Voltage and current
consumption data are available from the both M&C. Verify that values are within limits.
If M&C is not available, use a multimeter to verify that the appropriate voltages (24VDC
or 48 VDC) are present at the IBUC and Rx 1+1 Interface Module. The labeling on the
IBUC’s has the required voltage (24VDC or 48VDC).
Transmit Power Setting
There have been several cases where the transmit power has been turned up to or near
saturation while transmitting a digital carrier. This most likely will result in spectral
distortion, i.e., "shoulders", "ears", etc.
When transmitting digital carriers, it is customary to operate the power amplifier system
with an Output Back Off (OBO) sufficient to meet the spectral density mask
requirements.
TX IF Input Level Verification
If low or no TX output power is detected, start the troubleshooting by checking the input
to the Tx Redundant System. Use the following procedures:
- Check the TX Input Level displayed in M&C or disconnect the cable at the IBUC A
and B J1 (TX L-band) and use a spectrum analyzer to measure the power level of
the L-band signal at the output of the coaxial cable that connects to the IBUC’s at J1
(TX L-band). The L-band signal level should be between –20 and –55 dBm. If it is
not, check the cable and modem output.
- If the L-band signal is good, check that the 10MHz-reference signal is between +3
and –12 dBm and is distortion free. If it is not, check the cable and modem output (or
IFU TX OUT).
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