Comtech EF Data CDM-625 - Manual (Page 127)

CDM-625 Advanced Satellite Modem Revision 15
Front Panel Operation MN-CDM625
5–27
5.2.1.4.7 CONFIG: Rx  Descram (Descrambler)
Rx Descrambler = IESS (Normal,IESS,Off)
IESS-315 V.35 Scrambler ()
Use the ▲▼ arrow keys to select Normal, IESS, or Off, and then press ENTER.
The modem automatically selects the actual scrambler used for Normal, depending on the exact
operating mode:
• If framing = IBS/D&I, the IESS-309 scrambler is used.
• If Reed-Solomon is on but IBS/D&I is off, its frame synchronous scrambler is used per IESS-
310, App. H. An exception to this is legacy EF Data Reed-Solomon, which uses a proprietary
modified V.35 scrambler instead.
• If framing = EDMAC/2/3 and Reed-Solomon is off, its frame synchronous scrambler is used.
• If configured for TPC (Turbo) encoding and all of the above settings are off, the TPC frame
scrambler is used except for 8-QAM. For CDM-570 compatibility, TPC with 8-QAM uses the
V.35 scrambler.
• ITU V.35 scrambler (Intelsat variant) is the default scrambler when all of the above settings
are off.
When selecting IESS, the default ITU V.35 scrambler specified in IESS-315 takes priority over all
“normal” scramblers and is used instead. Therefore, for many operating modes, the two
scrambler choices are redundant.
When using TPC and Carrier-in-Carrier simultaneously, the IESS-315 (V.35) scrambler is the only
permitted choice.
5.2.1.4.8 CONFIG: Rx  Eq (Equalizer)
Rx Equalizer:
Disabled (Enable,Disable) ()
Use the ▲▼ arrow keys to select Enable or Disable, and then press ENTER. The integrated 5-tap
adaptive equalizer can compensate for:
• Amplitude slope and variation over the symbol bandwidth.
• Non-linear group delay variation over the symbol bandwidth.
It is particularly useful at higher symbol rates (up to 12.5 Msymbols/second) in situations with
long cable runs between equipment (downconverter and modem, for example).