Comtech EF Data CDM-625 - Manual (Page 346)

CDM-625 Advanced Satellite Modem Revision 15
DoubleTalk Carrier-in-Carrier Option MN-CDM625
10–16
10.4.7 Validate Carrier-in-Carrier Performance
Carrier-in-Carrier performance can be easily validated by verifying that Eb/No degradation due
to Carrier-in-Carrier is within published specification for the observed Power Spectral Density
Ratio.
Do these steps to validate Carrier-in-Carrier performance:
Step Task
1 Setup a conventional side-by-side link of the desired Eb/No:
 Carrier-in-Carrier should be OFF.
 Record the Eb/No as displayed by the Modems.
 Observe the 2 carriers on a spectrum analyzer and record the PSD ratio.
Example Link:
• Full duplex 512 kbps, QPSK, LDPC 2/3 circuit between 4.6 m and 2.4 m antennas
• Recorded Eb/No = 2.6 dB (at both modems)
• PSD Ratio = 1.2 dB (measured at larger Antenna)
2 Now relocate one of the carriers on top of the other carrier:
 Enable Carrier-in-Carrier.
 Record the Eb/No as displayed by the Modems.
3 Calculate change in Eb/No and verify against specification.
Example Link:
• Recorded Eb/No = 2.4 dB
• Change in Eb/No = 0.2 dB
• Eb/No Degradation (Spec.) at 1.2 dB PSD = 0.3 dB
• Modem performance is within spec