Comtech EF Data CDM-750 - Manual (Page 254)

CDM-750 Advanced High-Speed Trunking Modem Revision 2
Appendix C MN-CDM750
C–18
C.6 Monitoring ACM Performance and Statistics
• Chapter 3. REAR PANEL CONNECTORS
• Chapter 5. FRONT PANEL OPERATION
• Chapter 6. ETHERNET‐BASED REMOTE PRODUCT MANAGEMENT
• Chapter 7. SERIAL‐BASED REMOTE PRODUCT MANAGEMENT
The CDM‐750 provides a number of ways to monitor the ACM system:
• Via the CDM‐750 Front Panel: Use the MONITOR: ACM front panel menu to view the
current Tx and Rx ModCod , as well as the Local and Remote Es/No.
The Es/No displays values between –3.0 dB and +23.0 dB, with a resolution of 0.1 dB. If
either the local or remote demodulator is unlocked, the Es/No will display ‘No Sync’.
Note that you may often see that the RX ModCod is “00”. This is normal when there is
no real data being received. DVB‐S2 states that when no data is available, the modulator
should insert a Dummy PLFRAME. These Dummy PLFRAMEs are used to keep the demod
locked, but contain no user data and have a ModCod value of “00”.
If you wish to see the exact detail of the ModCod (data rate, modulation, code rate),
view these parameters using the INFO: TX or INFO: RX screens. Furthermore, if using
the CONFIG: TX or CONFIG: RX menus, both the symbol rate and data rate are
displayed. All of these screens update dynamically – if a ModCod changes, the
parameters are refreshed on these displays.
• Via the CDM‐750 Remote Control and Ethernet Management Interfaces: As described
for the CDM‐750 Front Panel, this information is available via remote queries issued
over the Remote Control Interface (Serial or Telnet), and by using the Ethernet Remote
Product Management Interfaces – SNMP, or the CDM‐750 Web Server interface via the
Status | Status and Status | ACM pages.
• Via Oscilloscope: If you have access to an Oscilloscope in X‐Y mode, Pins #3 and #11 on
the CDM‐750 rear panel J1 | ALARMS connector provide analog voltages to monitor the
constellation. The advantage here is that ModCod changes may be viewed
instantaneously.
• Via Internal BERT Tester: When using the Ethernet IP interface, it is not an easy matter
to verify BER performance. A way to verify that the ACM link is meeting performance is
by using the internal BERT tester. Not only will the internal BERT verify BER
performance, it is also tolerant of the change in bit rate that accompanies a change in
ModCod. The BERT can be used to confirm that there are no sync losses or bursts of bit
errors when a ModCod changes.