Hughes HX200, Installation Manual

Page: 43 / 160

Chapter 3 • Commissioning the HX200 satellite router
1038054-0001 Revision B
33
•
Transmitted 10 MHz Off - Typical installations use the
default value, unchecked (10 MHz is on to BUC).
•
Set Maximum Tx Power/Minimum Attenuation - See section
below for details.
•
Enable Spreading - Typical installations use the default value
- unchecked.
•
Use External 10 MHz Signal - Typical installations use the
default value - unchecked.
3. Click Save Configuration.
Set Maximum Tx
Power/Minimum Attenuation
These values are used to control the maximum output power a
modem can transmit. The reason this must be set correctly is so
that the BUC input level is not high enough to cause the BUC to
saturate. If the BUC saturates it can cause ACI, transmit carrier
distortion, or excessive power compared to other terminals, any of
which could cause network degradation or outage conditions.
The maximum modem output power is 0 dB, and there is an
attenuator that is used by the modem operational software to
control the output power. If the Set Maximum Tx Power box is
checked, then the terminal will ensure that the attenuation applied
to the output signal never drops below the configured Minimum
Attenuation value, effectively limiting the maximum modem
output power.
The appropriate Minimum Attenuation value must be calculated
based on the TX IFL cable length, cable attenuation, and BUC
maximum power input. To determine this setting, you must first
know the maximum allowable input level into the BUC. This is
found by taking the maximum allowable BUC power out in dB,
then subtracting the BUC gain. Then, knowing the cable loss over
the length of TX IFL in use, the maximum modem output value is
known, and therefore the Minimum Attenuation value can be
calculated.
As an example, assume we are using an ODU with a maximum
allowable power output of 36 dB, with a gain of 56 dB. The
maximum allowable input to the BUC in the ODU is -20 db (i.e.
36 dB - 56 dB). With a typical 100 foot cable run, where the cable
loss is 8 dB per 100 feet, the cable will introduce an 8 dB signal
loss. Thus the maximum allowable power out at the input to the
cable (i.e. the output from the modem) is -12 dB. Given the
modem output power with no attenuation is 0 dB, the Minimum
Attenuation value should be set at 12 dB.