Mocomtech SLM-5650 - Manual (Page 108)

SLM-5650 Satellite Modem Revision 1
Maintenance MN/SLM5650.IOM
5–6
5.2 Demodulator Checkout
Test the demodulator as follows:
Step Procedures
1 Set up the equipment as shown in Figure 5-1 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
with noise and without noise are shown in Figure 5-4.