Demodulator Tests; Dynamic Range; Acquisition Range; System Ber Test - Comtech EF Data SLM-7650 Installation And Operation Manual

SLM-7650 Satellite Modem
Maintenance
5.3.2

Demodulator Tests

The tests listed will give reasonable assurance that the demodulator section is performing
to specification. The test equipment used in these test is listed in Table 5-7. All
demodulator tests require connection to a known good modulator that is capable of being
configured to the same operating modes as the demodulator under test. These tests can
be run without a Noise test set, but the confidence level of the test is reduced.
5.3.2.1

Dynamic Range

1. In the Utility - Modem Type menu, configure the modem for modem type 7650-00.
2. Set the level into the demodulator for -15 dBm and an Eb/No of 5.0 dB.
3. Verify that the demod locks and the Fireberd syncs.
4. Set the level into the demodulator for -55 dBm and an Eb/No of 5.0 dB
5. Verify that the demod locks and the Fireberd syncs.
5.3.2.2

Acquisition Range.

1. Continue from the previous step and set the level into the demodulator for -40 dBm
and an Eb/No of 5.0 dB.
2. Verify that the demodulator locks and the Fireberd syncs.
3. In the Monitor menu, observe the frequency the demodulator Sweep Frequency
4. Set the IF frequency of the test modulator 70.025 MHz.
5. Turn on transmit power on the test modulator.
6. Verify that the demodulator locks and the Fireberd syncs.
7. In the Monitor menu, observe the frequency the demodulator Sweep Frequency
8. Set the IF frequency of the test modulator to 69.975 MHz.
9. Turn on transmit power on the test modulator.
10. Verify that the demodulator locks and the Fireberd syncs.
11. In the Monitor menu, observe the frequency the demodulator Sweep Frequency
5.3.3

System BER Test

1. Continue from the previous step but change the modulator and the demodulator data
rate to 1544 kbps, 1/2 rate CEVD.
2. Connect the demodulator input to the output of a Noise test set that is connected to
the modulator and a BER tester.
3. Verify that the demodulator operates within the specified Eb/No performance.
4. Additional data rates can be done to verify operation over the full data rate range.
BER testing can become very time consuming at low data rates.
Note: Accumulation of 20 error events (error seconds) is the generally considered a
valid BER test. For Reed-Solomon testing this can become extremely time
consuming.
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Revision 4
MN/SLM7650.IOM