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CDM-750 High Speed Trunking Modem
DoubleTalk Carrier-in-Carrier Option
8.3.1 Operational Details
The rules for CnC operation can be summarized thusly:
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Both earth stations share the same satellite footprint, so each sees both carriers;
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CnC carriers are operated in pairs;
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One outbound with multiple return carriers is not allowed;
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Asymmetric operation is allowed up to a 3:1 ratio of symbol rate;
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The ratio of CnC (ratio of interferer power to desired power) is normally within ±7 dB;
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CnC operates with modems – not modulators only or demodulators only.
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During CnC acquisition, neither modem passes data. Only after both modems complete
the CnC acquisition process does data flow.
For best operation, observe the following:
•
Keep the search delay range as narrow as possible – once the modem has reported the
search delay, narrow the search delay range to the nominal reported value +/- 10 ms; for
example, if the modem reported delay is 245 ms, narrow the search range to 235-255 ms.
Factory default for search delay is 230-290 ms. Search delay programmable range is
0-400 ms, where 0 ms is used when doing loop-back or bench testing.
•
Use the CDM-750's Internal BERT Tester when evaluating CnC performance.
8–4
Revision 1
MN-CDM750
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