Comtech EF Data CDM-570A - Manual (Page 533)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Appendix G Revision 2
G–15
Step Task
 Using a spectrum analyzer, measure Co+No/No at the input to the modem at Site B.
 Measure/record Eb/No at Site A. Make sure there is sufficient margin to account for CnC.
 Measure/record RSL at Site B.
3 Using Co+No/No readings calculate PSD ratio at Site A and Site B. If it is not within specification, make
necessary adjustments to bring it within specification and repeat measurements in Step (1) and (2).
 Also verify that the RSL is within spec.
4 Now without changing the transmit power levels, turn ON both the carriers (on the same frequency) and
turn CnC ON.
 Measure/record Eb/No at Site A and B.
 Measure/record RSL at Site A and B.
 Now compare Eb/No in presence of 2 over lapping carriers with CnC with Eb/No when only 1
carrier was ON. Eb/No variation should be within spec for that modulation, FEC and PSD ratio.
5 The test can be repeated for different PSD ratio and Eb/No.
G.4.6 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.
Comtech EF Data recommends the following steps for validating 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, VersaFEC 0.631 circuit between 4.6 m and 2.4 m antennas
• Recorded Eb/No = 2.7 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.