Specifications

DMD20/20LBST Universal Satellite Modem Theory of Operation
MN-DMD20-20LBST Revision 14 3–28
3.15.3 Operational Recommendations
The rules for CnC operation are summarized below:
• Both earth stations share the same footprint so each sees both carriers;
• CnC carriers are operated in pairs;
• One outbound with multiple return carriers is not allowed;
• Asymmetric data rates are allowed (see Section 3.15.15 for CnC specifications);
• The ratio of power spectral density is normally less than 11 dB;
• CnC operates with modems – not modulators only or demodulators only.
In addition, to minimize ‘false’ acquisition, observe the following:
• Use of IESS-315 V.35 Scrambler is highly recommended;
• 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 +/- 5 ms – for
example, if the modem reported delay is 245 ms, narrow the search range to say 240 –
250 ms.
• Use external data source (e.g. Firebird) or internal BER tester when testing Carrier-in-
Carrier performance.
• To prevent self-locking in case the desired carrier is lost, it is recommended that the two
carriers have some configuration difference – for example, use different settings for
Spectrum Inversion.