Comtech EF Data CDD-880, Installation And Operation Manual

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CDD-880 Multi Receiver Router MN-CDD880
Appendix G Revision 2
G–10
When you disable DPC, the CDM-840 notifies the CDD-880 and modifies the timer check logic,
changing the target window to E
S
/N
0
below .5 dB and/or MODCOD is not at maximum. The
reason for this change is, with DPC disabled, the power level is set to Current Power+Margin
Moving Power>Target Power; if not changed, the timer would be at fast rate indefinitely. This
change also allows ACM to operate normally without DPC.
G.3.1.2 ACL Timers
Timers on both sides on the link are required to maintain quality and reduce hysteresis, with
each end having a specific and separate function:
•
CDD-880 Messaging Timers – CDD-880 timers are state-driven on when to send the next
LQRM:
o
Every 500 ms, send E
S
/N
0
data

Unlocked, E
S
/N
0
outside target window or max MODCOD mismatch.
o
Every 60 seconds, send E
S
/N
0
data, keep-alive

Locked, E
S
/N
0
= Target (target window ±.5 dB)
• CDM-840 Power Adjustment Timers – CDM-840 timers are dependent on receipt or loss of
LQRM:
o
Targeting Power adjustment (ratcheted steps)

.3 dB every 100 ms steps >1 dB

.1 dB targeting steps <1 dB
o
Timeout on 60-second intervals

Two consecutive missed messages, 120 seconds

Drop to BPSK, go to rated max power

Four consecutive missed messages, 240 seconds

Recovery Mode, loss of LQRM, remove demod from active control list

Stay at BPSK until next LQRM
G.3.1.3 LQRM Failure and Recovery Steps
1.
If the LQRM indicates a loss of lock, the new power value is immediately set to the rated or
maximum power as an attempt to regain communication.
2. Once the power value changes, a timer prevents further power value or MODCOD changes
for a duration of 800 ms; this helps prevent the CDM-840 from modifying the power value
on the basis of stale data.
3. If a CDM-840 hasn't received an LQRM from the CDD-880 in 120 seconds (two consecutive
slow rate missed messages), it drops into recovery mode, adjusting the power value to rated
or maximum adjusting MODCOD to BPSK.