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SDM-300A Satellite Modem
5.1.2
Modulator Checkout
Use the following procedure to check out the modulator:
1. Set up the equipment as shown in Figure 5-1. Refer to
2. Set up the modem for operation by using the Configuration Modulator and
3. Clear all TX faults by correct use of data and clock selection (Chapter 4).
4. Measure the E
5. Connect a spectrum analyzer to the modem as shown in Figure 5-1. Ensure the IF
6. To check the frequency and phase modulation accuracy:
Rev. 4
specifications.
Demodulator front panel menus.
/N
with a receiver that is known to be properly operating. Refer
b
0
to Table 5-1 and Figure 5-2 to check for proper E
measured by taking the average level of the noise and the average level of the
modem spectrum top. Use this measurement for the first column on Table 5-1.
Read across the page to find the S/N and E
Once the demodulator has locked to the incoming signal, the Monitor menu will
display signal level, raw BER, corrected BER, and E
examples of BER performance curves.
output meets the appropriate mask and spurious specifications. Measure the
power output at different levels and frequencies.
A typical output spectrum is shown in Figure 5-3.
a. Set the modem to the continuous wave Normal mode by using the Carrier
Mode front panel menu
condition. A pure carrier should now be present at the IF output. This should
only be used for frequency measurements. In this mode, spurious and power
measurements will be inaccurate.
b. Set the modem to the continuous wave Offset mode by using the Carrier
Mode front panel menu
side-band-suppressed carrier signal. Ensure the carrier and side-band
suppression is < -35 dBc.
/N
b
/N
for the specific code rate.
b
0
(Chapter
3). This sets the Carrier mode in the off
(Chapter
3). This generates a single, upper
Maintenance
Chapter 4
for modulator
level. The (S+N)/N is
0
/N
. Refer to
Chapter 1
b
0
for
5–3
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