Comtech EF Data CRS-500 - Manual (Page 91)

CRS-500 1:N Redundancy System Revision 2
Cables and Connections MN-CRS500
4–35
4.4.3 IF Cable Connections – Multiple Transponders (Using ISUs)
When Traffic Modems use multiple transponders, the CRS-500’s CRS-282xx IF Switch Units (IFUs)
provide routing, control and isolation of all the modems’ IF signals – all Traffic and Redundant
modem IF signals are routed through the ISUs.
Because relays on the CRS-282xx isolate any unwanted signals, non-faulted modems are always
connected to the correct up/down converters (transponders); furthermore, as the CRS-500
automatically senses the presence of CRS-282xx ISUs, the offline modem’s Tx IF remains on.
The ISUs are available in separate Tx IF and Rx IF Units, accommodating either 70/140 MHz Band
or L-Band operation. The ISU’s modular design permits different ISU combinations as needed to
cover multiple transponders operating either on the same IF-Band or on different IF-Bands.
The table provided under Sect. 4.1.1.3 IF Switch Unit (ISU) Configurations lists the available
ISUs and their pertinent CEFD IF cables. Figures in the sections that follow show 1:N IF cable
connections between Redundant and Traffic Modems and select CRS-282xx ISUs. Cabling
requirements are dependent on the ISUs in each configuration.
4.4.3.1 Same Band (Tx / Rx, Tx or Rx) / Multiple Transponder
Configurations
One Tx ISU and one Rx ISU are required when all Traffic Modems in the CRS-500 1:N
Redundancy System operate in either of the following configurations:
• Tx / Rx – On the same IF-Band (i.e., either 70/140MHz Band or L-Band) for both Tx and
Rx, or
Figure 4-13 provides an example of a same band / multiple transponder Tx / Rx
configuration. Here, a 1:N redundancy setup using CRS-282T50 and CRS-282R50 ISUs
with CDM-625 modems is shown with 70/140 MHz as the Tx and Rx IF-Bands.
• Tx or Rx – On the same IF-Band for Tx or Rx (e.g., 70/140MHz Band for Tx, and L-Band
for Rx).
Figure 4-14 provides an example of a same band / multiple transponder Tx or Rx
configuration. Here, a 1:N redundancy setup using CRS-282T50 and CRS-282RL ISUs with
CDM-625 modems is shown with 70/140 MHz as the Tx IF-Band and L-Band as the Rx IF-
Band.
For either configuration, make IF cabling connections as follows:
First, for the Redundant Modem, using the appropriate IF cables:
• Connect the pertinent “Tx IF” connector on the modem to the connector labeled “Tx
REDUNDANT MODEMS | FROM MODEM 1” on the CRS-282Txx ISU, and