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P300H P300 Series Modem Installation and Operating Handbook Page 155
In Maint' Eb/No mode the Target Eb/No has to be set as well as a Tolerance window. Only when the
target Eb/No tolerance is exceeded is the Tx power adjusted to bring the distant Eb/No back to the target
value. The Tx power will only continue to be adjusted automatically until the Eb/No settles on the target
value. This prevents continual Tx power variations under normal minor thermal noise variations. Once
settled on the target Eb/No the Tx power adjustment will only be automatically reactivated when the Eb/No
tolerance is again exceeded.
Separate upper and lower Tx power limits are set along with a slew rate limit (if it is felt that additional limits
to prevent rapid power variations are required). By manipulating the upper and lower power limits one of
three scenarios can be achieved:
+/- Limits: Constant performance: Always uses the power required to maintain the Eb/No.
Provided the limits are not reached the link performance will stay as it is (subject to
the tolerance window).
+ Limit only: Best performance: The power will increase when required by a fade bit it will not
reduce. Any especially good atmospheric conditions will improve the Eb/No beyond
the current level.
- Limit only: Power economy: The power will not increase, but it will reduce if there are any
especially good atmospheric conditions that allow less power to achieve the target
Eb/No.