Operational Recommendations - Comtech EF Data DMD50 Installation And Operation Manual

DMD50 Universal Satellite Modem

3.14.3 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 (no restrictions);
•
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.
MN-DMD50– Revision 3
Theory of Operation
3–24