Comtech EF Data CDM-600/600L - Manual (Page 40)

CDM-600/600L Open Network Satellite Modem Revision 3
Introduction MN/CDM600L.IOM
1–12
1.3.7 Data Interfaces
The CDM-600/600L includes, as standard, a universal data interface that eliminates the need to
exchange interface cards for different applications. The interfaces offered include:
• RS-422 (RS-530) DCE (at rates up to 10 Mbps)
• X.21 DTE and DCE (at rates up to 10 Mbps)
• V.35 DCE (at rates up to 10 Mbps)
• Synchronous RS-232 DCE (at rates up to 300 kbps)
• G.703 E1, balanced and unbalanced
• G.703 T1, balanced
• G.703 E2, balanced and unbalanced
• G.703 T2, balanced
• Serial LVDS (at rates up to 20 Mbps)
• Dual Audio, 600Ω (produces a single 64 kbps IBS data stream)
1.3.8 Verification
The unit includes many test modes and loopbacks for rapid verification of the correct function of
the unit. In particular, the IF loopback permits the user to perform a quick diagnostic test without
disturbing external cabling. During the loopback, all the Rx configuration parameters are
temporarily changed to match the Tx side, and an internal RF switch connects the modulator
output to the demodulator input. When normal operation is again selected, all of the previous
values are restored.
1.3.9 AUPC
An important feature in the CDM-600/600L 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, either the EDMAC or D&I++ or ESC++ framing types may 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 adjusts its output
power, and a closed-loop feedback system is created over the satellite link.
A benefit of this AUPC feature is that the remote demodulator’s Eb/No can be viewed from the
front panel display of the local modem.
See Chapter 7. Automatic Uplink Power Control (AUPC) for further information.
1.3.10 EDMAC
To facilitate network management for small networks, the CDM-600/600L incorporates the
proprietary Embedded Distant-end Monitor And Control (EDMAC). In this mode, an additional
5% overhead is combined with the traffic data, (1.6% in Turbo BPSK modes, Turbo Rate 21/44