Comtech EF Data CDM-750, Installation And Operation Manual

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CDM-750 Advanced High-Speed Trunking Modem Revision 2
Appendix D MN-CDM750
D–16
D.4.7 Commissioning and Deploying Carrier-in-Carrier
Prior to commissioning a Carrier ‐ in ‐ Carrier link, it is critical that the link is fully tested
in
non-CnC mode
and all system issues – including external interference, antenna
pointing, cabling, and SSPA backoff – are resolved. Only after the link is robust
should the user attempt turning on CnC.
Comtech EF Data recommends that you follow these steps to commission and deploy CnC:
Step Task
1 Turn ON the carrier at Site A. Carrier from Site B is OFF. CnC function is OFF at both sites.
¾
Using a spectrum analyzer, measure Co+No/No at the input to the modem at Site A.
¾
Using a spectrum analyzer, measure Co+No/No at the input to the modem at Site B.
¾ Measure/record Es/No at Site B. Make sure there is sufficient margin to account for CnC.
¾
Measure/record Receive Signal Level (RSL) at Site B, usually midrange.
2 Turn OFF the carrier at Site A. Turn ON the carrier at Site B. CnC function is OFF at both sites.
¾ Using a spectrum analyzer, measure Co+No/No at the input to the modem at Site A.
¾
Using a spectrum analyzer, measure Co+No/No at the input to the modem at Site B.
¾ Measure/record Es/No at Site A. Make sure there is sufficient margin to account for CnC.
¾
Measure/record RSL at Site B.
3 Using Co+No/No readings, calculate CnC ratio at Sites A and B. If it is not within specification, make
necessary adjustments to bring it within specification and repeat measurements in Steps 1 and 2.
¾ 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.
¾
Measure/record Es/No at Sites A and B.
¾ Measure/record RSL at Sites A and B.
¾
Now, compare Es/No in the presence of two overlapping carriers with CnC with Es/No when
only one carrier was ON. Es/No variation should be within spec for that modulation and SR
ratio.
5 You may repeat the test for different SR ratios and modulation types.