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QMultiFlex-400™ Installation and Operating Handbook
acquisition time by setting minimum and maximum delay values based around the
calculated value. It can also be compared to the actual satellite delay reported on the Status
screen.
8.3.4.3 Lab Configuration
If initially testing the Hub canceller in a lab environment, where the hub and remote modems
are co-located, the RTD will be approximately 0 (unless a satellite delay simulator is used
in the signal path) as there will be no significant delay in the echoed signal. In such a case,
set the RTD control to `Set delay` and simply set the minimum delay to 0.01ms (the
minimum value) and the maximum delay to 0.05ms, as below:
Figure 8-12 - Hub Canceller Menus - Lab Configuration
8.3.4.4 Paired Carrier Enable
Enable the canceller using the tick box. Depending on the type of Round-Trip Delay, initial
acquisition usually takes between 15 to 60 seconds. The delay acquisition progress can be
viewed on the modem's `Status` page. When the canceller comes into lock, the
downstream demodulators should also lock, as should the down-stream FEC decoder etc.
On the status Web GUI page, the canceller will report the RTD in milliseconds to a
resolution of 1μs. It will also report the near/far carrier power ratio; that is, the ratio in power
between the received echo and the signal of interest being received from the far stations.
Furthermore, the offset frequency of the received echoed carrier will also be displayed.
To view the Hub Canceller graph, select View > Graphs > Spectrum and use the sub menu
`Select` and drop down to the PCMA graph. A two-trace spectrum will be displayed, as
shown in figure 8-13. The red trace shows the signal spectrum as received by the canceller
off satellite. The blue trace shows the signal spectrum exiting the canceller and being
presented to the downstream demodulators. Note: the IB carriers don't all have to be
contained within the OB carrier bandwidth; they can overspill if there are more carriers than
will fit under the outbound. Please refer to the examples in figures 8-14 and 8-15. If the
canceller fails to lock, refer to the troubleshooting guide within the following sections.
8-13
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