Comtech EF Data CDM-600/600L - Manual (Page 132)

CDM-600/600L Open Network Satellite Modem Revision 3
Forward Error Correction Options MN/CDM600L.IOM
6–12
CAUTION
When using Firmware Versions prior to 1.3.0 for the CDM-600L and Firmware
Versions prior to 1.3.1 for the CDM-600, Comtech EF Data strongly cautions users
when using uncoded operation. If the acquisition sweep width exceeds one
quarter of the symbol rate, there is a very high probability that the demodulator
will false lock. For Firmware version 1.3.0 or higher for the CDM-600L, and FW
Ver. 1.3.1 or higher for the CDM-600, the problem has been been eliminated.
Example 1: A Firmware Version prior to 1.3.0 for the CDM-600L (FW Ver. 1.3.1 for
the CDM-600) is being used, and the user selects 64 kbps QPSK, uncoded. The
symbol rate will be half of this rate, or 32 ksymbols/second. One quarter of this
equals 8 kHz. Therefore, the absolute maximum acquisition sweep range which
should be considered is
±
8 kHz. If there is any frequency uncertainty on the
incoming carrier, this should be subtracted from the sweep width. The problem
becomes progressively better with increasing symbol rate.
Example 2: A Firmware Version of 1.3.0 (FW Ver. 1.3.1 for the CDM-600), or higher
is used. There is no limitation on acquisition sweep width.
Comtech EF Data cannot be held responsible for incorrect operation if the user does not adhere to
these guidelines when using uncoded operation.