Newtec MDM6000 - Back Ground Information

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Feature Descriptions MDM6000 Satellite Modem
14.8.2 Back Ground Information
Automatic Level Control Mode
Transponders that operate in ALC (Automatic Level Control) mode have a mechanism where a
detector at the input of the transponder measures the input power. If it decreases (due to fading in
the uplink), the gain will be increased in order to maintain a fixed downlink power. ALC operation is
typically found in single carrier per transponder operation such as uplink for DTH systems.
The AUPC mechanism used in the MDM6000 Satellite Modem is incompatible with
transponders set to ALC mode.
Fixed Gain Mode
In transponders operating in multi-carrier mode, ALC is not applicable. This is because not all links
exhibit fading at the same time so compensating the gain of the transponder for fading of a link will
have a negative effect on the other non-faded links and could cause intermodulation. These
transponders are said to operate in FGM (Fixed Gain Mode).
AUPC can be operated under the following conditions:
• Multi carrier/transponder mode with the transponder in Fixed Gain Mode;
• Single Carrier/transponder mode with the transponder in Fixed Gain mode.
In many large earth stations there is no need for AUPC in the modem as AUPC is
implemented in an external system that is based on a beacon receiver.