Comtech EF Data CDM-570A - Manual (Page 44)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Introduction Revision 2
1–10
1.2.5 Verification
The modem includes many test modes and loopbacks for rapid verification of correct modem
function. The IF loopback, in particular, permits execution of a quick diagnostic test without
disturbing external cabling. During the loopback, all the receive configuration parameters
temporarily change to match the transmit side, and an internal RF switch connects the
modulator output to the demodulator input. All of the previous values are restored once normal
operation is again selected.
1.2.6 AUPC
APPENDIX E. AUPC (AUTOMATIC UPLINK POWER CONTROL)
AUPC (Automatic Uplink Power Control) is an important feature that enables the modem to
automatically adjust its output power to maintain as constant the E
b
/N
0
of the remote end of
the satellite link. This provides protection against rain fading, a particularly severe problem with
Ku-Band links.
Note that you can simultaneously use both EDMAC and AUPC. A benefit of AUPC is that,
whenever you select EDMAC/AUPC operation, you can view the remote demodulator’s E
b
/N
0
from the front panel display of the local modem.
To accomplish AUPC, you must use the framed EDMAC mode of operation. The distant end
modem constantly sends back information about the demodulator E
b
/N
0
using reserved bytes in
the overhead structure. The local modem uses the E
b
/N
0
to adjust its output power and create a
closed-loop feedback system over the satellite link.
1.2.7 EDMAC
Appendix J. EDMAC CHANNEL
EDMAC (Embedded Distant-end Monitor And Control) facilitates network management for small
networks. In this mode, an additional 5% overhead is combined with the traffic data, (1.6% in
Turbo BPSK modes, Turbo Rate 21/44 QPSK/OQPSK, and all data rates greater than 2 Mbps).
M&C information is added transparently, allowing access to the distant-end modem.
Additionally, EDMAC-2 uses 1.6% overhead in all modes for those applications where the 5%
overhead is excessive. The EDMAC and EDMAC-2 modes do not require any additional cabling at
either the local or the distant-end Modems.
The standard M&C control port provides access to EDMAC. Full monitor and control is possible,
and you may control the on/off status at the distant-end carrier.