Demodulator Checkout - Comtech EF Data SDM-300A Installation And Operation Manual

Maintenance
5.1.3

Demodulator Checkout

Use the following procedure to test the demodulator.
1. Set up the equipment as shown in Figure 5-1. Refer to
2. Set up the modem with an external IF loop and level. Use a properly operating
3. Allow the modem to lock up. Depending on the data rate and overhead type,
4. Set up the modem to check the constellation patterns with an oscilloscope that is
5–6
demodulator specifications.
modulator, and ensure that power levels, data rates, code rates, etc., are
compatible.
lock up may take several seconds. When the green carrier detect LED is on and
the DEMUX lock fault has been cleared (where applicable), the modem will run
at the specified error rate. Run the TX power level (input amplitude) over the
full range, and offset the TX frequency from the RX frequency by 35 kHz.
Ensure the modem still runs within the specified error rate.
set in the X-Y mode. Typical constellation patterns with noise and without noise
are shown in Figure 5-4. These test points are available on the auxiliary
connector (J9, pins 6 and 8). It is not necessary to open the modem to look at
these test points.
SDM-300A Satellite Modem
Chapter 4 for the
Rev. 4