Comtech EF Data CDM-550T - Manual (Page 22)

CDM-550T Satellite Modem Revision 3
Introduction MN/CDM550T.IOM
1.2.1 AUPC
An important innovation in the CDM-550T is the addition of Automatic Uplink Power Control
(AUPC). This feature enables the modem to automatically adjust its output power to maintain the
Eb/No of the remote end of the satellite link constant. This provides protection against rain
fading, a particularly severe problem with Ku-band links.
To accomplish this, the framed (EDMAC) mode of operation must be used, and the distant end
modem constantly sends back information about the demodulator Eb/No using reserved bytes in
the overhead structure. Using the Eb/No, the local modem then adjusts its output power, and
hence, a closed-loop feedback system is created over the satellite link.
A benefit of this feature is that whenever framed operation is selected, the remote demodulator’s
Eb/No can be viewed from the front panel display of the local modem. Note that both EDMAC
and AUPC can be used simultaneously.
1.2.2 Software
The internal software is both powerful and flexible, permitting storage and retrieval of up to 10
different modem configurations. The modem uses ‘flash memory’ technology internally, and new
firmware can be uploaded to the unit from an external PC. This simplifies software upgrading,
and updates can now be sent via the Internet, E-mail, or on disk. The upgrade can be performed
without opening the unit, by simply connecting the modem to the serial port of a computer.
1.2.3 Verification
The unit includes many test modes and loopbacks for rapid verification of the correct functioning
of the unit. Of particular note is the IF loopback, which permits the user to perform a quick
diagnostic test without having to disturb external cabling. During the loopback, all of the receive
configuration parameters are temporarily changed to match those of the transmit side. When
normal operation is again selected, all of the previous values are restored.
1.2.4 Data Interfaces
The CDM-550T includes, as standard, a universal data interface which eliminates the need to
exchange interface cards for different applications. The interfaces offered include:
• RS-422 (RS-530) DCE
• V.35 DCE
• Synchronous RS-232 DCE
• Asynchronous RS-232 (at data rates up to 56 kbaud)
• X.21 DTE and DCE
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