Comtech EF Data DT-4500-A Series - Manual (Page 154)

DT-4500-A Series Downconverters Revision 0
Appendix B MN-DT4500A
B–14
• Chain Length (Backup Unit): Use the drop-down list to select N/A, or 1:1 through 1:12.
• Polarity (Primary Down Converter): Use the drop-down list to select N/A, Single, or Dual.
Click [Change] to save.
Forced Backup
Use the drop-down list to set the Forced Backup as NONE, or Unit 01 through Unit 12, and then
click [Change].
Redundancy Mute Mode
Use the drop-down list to set the Redundancy Mute Mode as OFF or ON, and then click
[Change].
Primary Unit Status
This section is populated on a per-unit basis as the daisy chain is configured. Information is
provided for each unit’s Online Status (Online or Offline), Operating RF Frequency, Attenuation,
Mute status, and Polarity. Additionally:
• Auto Mode: Use the drop-down list to select a unit’s switching mode as Manual or
Automatic.
• Offset: Enter an offset adjustment value here. See Sect. B.4.3 for additional information.
Click [Change] to save.
B.4.3 Offset Adjustment
The offset is used to compensate for cable and switch losses. When the system is initially set up
and tested, each downconverter needs to be forced to backup and the offset adjusted to
minimize gain mismatch between the normal and bypassed mode. This offset will be different
for each downconverter and is stored in a table in the backup unit. Follow these steps to set the
offset:
Step Description
1 Connect a signal source to the input and a power meter or spectrum analyzer to the output of the first
online downconverter.
2 Record the output power.
3 Force a backup of the first online unit and adjust the offset until the output power matches what was
recorded in Step 2.
4 Restore the online unit and repeat for the other online units.