Comtech EF Data C5 - Manual (Page 227)

C5/K1/K3 Integrated Satellite Terminal System System Checkout
Rev. 0 6-3
6.2.1 Modulator Checkout
Use the following procedure to check out the modulator:
1. Set up the equipment as shown in Figure 6-1. Refer to Chapter 2 for modulator
specification.
2. Set up the IDU for operation by using the Configuration Modulator and
Demodulator front panel menus.
3. Clear all transmit faults by correct use of data and clock selection (Chapter 4).
4. Measure the E
b
/N
0
with a receiver that is known to be properly operating. Refer
to Table 6-1 and Figure 6-2 to check for proper E
b
/N
0
level. The (S+N)/N is
measured by taking the average level of the noise and the average level of the
IDU spectrum top. Use this measurement for the first column on Table 6-1. Read
across the page to find the S+N and E
b
/N
0
for the specific code rates.
Note: Once the demodulator has locked to the incoming signal, the Modulator
menu will display signal level, raw BER, corrected BER, and E
b
/N
0
. Refer to
Chapter 2 for examples of BER performance curves.
5. Connect a spectrum analyzer to the IDU as shown in Figure 6-1. Ensure the IF
output meets the appropriate mask and spurious specifications. Measure the
power output at different levels and frequencies.
Note: A typical output spectrum is shown in Figure 6-3.
6. To check the frequency and phase modulation accuracy:
a. Set the IDU to the continuous wave Center-CW by using the Carrier Mode
front panel menu (Chapter 4). 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 IDU to the continuous wave Offset mode by using the Carrier Mode
front panel menu (Chapter 4). This generates a single, upper side-band
suppressed carrier signal. Ensure the carrier and side-band suppression is
" -35 dBc.