Comtech EF Data SLM-5650A - Manual (Page 328)

SLM-5650A Satellite Modem Revision 8
Appendix A MN-SLM5650A
A–6
A.2.3 Demodulator Checkout
Use the following procedure for demodulator checkout:
Step Task
1 Set up the equipment as shown in Figure A-1 using the 70/140 MHz IF interface.
2 Set up the modem with an external IF loop and level. Use a properly operating modulator, and ensure
that power levels, data rates, code rates, etc. are compatible.
3 Allow the modem to lock up.
a. Depending on the data rate and overhead type, lock-up may take several seconds.
b. When the GREEN IF and Data Lock LED are ON and any fault has been cleared (where
applicable), the modem will run at the specified error rate.
c. Run the Rx power level (input amplitude) over the full range and offset the Tx frequency from
the nominal Rx frequency by up to ±30 kHz.
d. Ensure the modem still runs within the specified error rate.
4 Set up the modem to check the constellation by hooking an oscilloscope that is set in the X-Y mode to
J9 pins 3 and 8. An alternative method is to use a computer and the IQ Mon program with an Ethernet
connection to the modem. Typical constellation patterns are shown with noise (Figure A-4) and without
noise (Figure A-5).