Comtech EF Data RCF6001 - Manual (Page 26)

Maintenance RCF6001 Satellite Terminal
Page 4-6 TM082 - Rev. 1.0
The AUPC menus are located under the Modulator Menu as shown schematically below:
The basic AUPC operation is described as follows: Assume that the two modems, one at each end of the
link, are set to AUPC operation. Only one direction is discussed, but the same functions could be
occurring in both directions simultaneously. Modem “A” is transmitting to modem “B” under normal
conditions and modem “B” has a receive Eb/No of 7.5 dB. Modem “A” has been set to an AUPC Eb/No
on the front panel of 7.5 dB, and is currently outputting –15 dBm. Next, it begins raining at location “B”,
and the Eb/No drops to –7.0 then –6.8 dB. Modem “B” is constantly sending update messages to “A” and
reports the current Eb/No. When “A” sees the drop in Eb/No, it slowly begins to raise the output power,
and raises it again when it sees further drops. As the rain increases in intensity, and the Eb/No decreases
again, “A” continues to increase its power level to compensate, and when the rain diminishes and quits, it
also lowers its power level to compensate. The operation is therefore a feedback control loop with the
added complication of a significant time delay.
There are safeguards built into the AUPC system. First, the Modulator has two additional parameters that
allow control of the maximum and minimum power output level. Second, a default power level is
specified which takes precedence over the output power level during signal loss or loss of AUPC channel
communication. The default power level should normally be set to a high enough level to reestablish
communication regardless of rain fade. The other controls are built into the operating control software to
limit response times and detect adverse operating conditions.
3.7 DMD2401 Asynchronous Overhead Operation
3.7.1 Asynchronous Framing/Multiplexer Capability
The Asynchronous Framing/Multiplexer is capable of multiplexing a relatively low-speed overhead
channel onto the terrestrial data stream resulting in a slightly higher combined or aggregate data rate
through the modem. The overhead channel is recovered at the far end. This added channel is termed
variously an overhead channel, service channel, async channel or in IESS terminology an ES to ES data
(If Installed)