Modulator Tests; Spectral Shape Of The If Output; Carrier Null; Figure 5-6. Dual Test Mode - Comtech EF Data SLM-7650 Installation And Operation Manual

SLM-7650 Satellite Modem
Maintenance
5.3.1

Modulator Tests

The tests listed will give reasonable assurance that the modulator section is performing to
specification. The test equipment used in these test is listed in Table 5-7.
5.3.1.1

Spectral Shape of the IF Output

1. In the Utility - Modem Type menu, configure the modem for modem type 7650-00.
2. In the Configuration - Modulator menu turn the modulator TX IF Output ON.
3. Connect the modulator output to a Spectrum Analyzer.
4. Set the Spectrum Analyzer to a center frequency of 70MHz, frequency span of 100
KHz, and resolution bandwidth to 3 kHz. Set the reference level to see the
modulated spectrum on the spectrum analyzer screen.
5. Verify that the output spectral density mask meets MIL-STD-188-165 Section
5.1.6.4.1 and its associated Figure 4
5.3.1.2

Carrier Null

1. Continue from the previous step and in the Configuration -Modulator menu, set the
Carrier Mode to DUAL (Figure 5-6).
2. On the Spectrum Analyzer, verify that the center carrier null is greater than 35 dB.
3. Change the Carrier Mode to OFFSET(Figure 5-7).
4. On the Spectrum Analyzer, verify that the offset carrier null is greater than 30 dB.
5. Set the Carrier Mode to Normal-Modulated.
6. Turn the TX-IF Output ON.

Figure 5-6. DUAL Test Mode

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