Comtech EF Data CDM-625 - Manual (Page 345)

CDM-625 Advanced Satellite Modem Revision 15
DoubleTalk Carrier-in-Carrier Option MN-CDM625
10–15
10.4.6 Carrier-in-Carrier Commissioning and Deployment
Prior to commissioning a Carrier-in-Carrier link, it is critical that the link is fully tested in non
Carrier-in-Carrier mode and all system issues including external interference, antenna pointing,
cabling, SSPA backoff are resolved. Only after the link is robust, should you attempt turning on
Carrier-in-Carrier.
Do these steps for Carrier-in-Carrier commissioning and deployment:
Step Task
1 Turn ON the carrier at Site A. Carrier from Site B is OFF. CnC function is OFF at both sites.
 Using a spectrum analyzer, measure Co+No/No at the input to the modem at Site A.
 Using a spectrum analyzer, measure Co+No/No at the input to the modem at Site B.
 Measure/record Eb/No at Site B. Make sure there is sufficient margin to account for
CnC.
 Measure/record Receive Signal Level (RSL) at Site B.
2 Turn OFF the carrier at Site A. Turn ON the carrier at Site B. CnC function is OFF at both sites.
 Using a spectrum analyzer, measure Co+No/No at the input to the modem at Site A.
 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.