Comtech EF Data CIM-300L - Manual (Page 139)

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Chapter 7.
System Checkout/Fault Isolation
7.1 S
YSTEM
C
HECKOUT
CAUTION
This equipment contains parts and assemblies sensitive to damage by ESD.
Use ESD precautionary procedures when touching, removing, or inserting
PCBs.
This Chapter is for testing and troublshooting base satellite modem functions and does
not cover the CiM IP module. For IP module testing and troublshooting, refer to Chapter
12, CiM IP Module Checkout and Fault Isolation .
7.1.1 M
ODULATOR
C
HECKOUT
Use the following procedure to check out the modulator:
1` To properly verify Modulator/Demodulator operation, an L-Band Noise generator needs to
be connected between the Tx and Rx of the CiM-300L.
Additionaly, a Spectrum Analizer and Oscilloscope will be needed to monitor modem
performance.
2 Set up the modem for operation by using the Configuration Modulatorand Demodulator
front panel menus.
3 Measure the Eb/No with a receiver that is known to be properly operating. Refer to Table
7-1 and Figure 7-2 to check for proper Eb/No level. The (S+N)/N is 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 7-1. Read across the page to find the S/N and
Eb/No for the specific code rate.
4 Once the demodulator has locked to the incoming signal, the Monitor menu will display
signal level, raw BER, corrected BER, and Eb/No.
5 Connect a spectrum analyzer to the modem. Ensure the IF 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 7-1.
6 To check the frequency and phase modulation accuracy: