Paradise Datacom Vision Series Installation And Operating Handbook page 105

Vision Series Installation and Operating Handbook
properly if an incompatible/older version of the JRE is installed (see the w eb page Help
box for more information).
The first time that a graph is displayed, the follow ing message w ill pop up. This is
because the Java applet requires privileges to run and therefore includes a security
certificate. The applet does not write any information to storage on the PC and is not
harmful in any w ay; you should select Yes in order to be able to view graphs.
Java Applet Security Warning Screen
7.4.2.1 Spectrum Graph
An example spectrum graph is show n overleaf. This can be used to check for correct
modem operation. The spectrum can be view ed in one of three modes.
In narrow view , the w idth of the spectrum is limited to less than tw i c e the symbol rate.
This mode does not interfere w ith modem operation in any w ay.
In wide view , the spectrum w idth is nearer to four times the symbol rate and this can be
used for checking for adjacent interfering carriers. In wide mode, the demodulator is
reprogrammed with different values to norm al operation and consequently the wide
m ode of operation is only available as a special test mode (since it would otherw ise
interfere w ith any traffic).
In super-wide view , which can be used without interfering w ith traffic, the spectrum w idth
is set to 50MHz to allow all or a significant portion of the satellite transponder bandw idth
to be monitored. ( Note that super-w ide mode requires a symbol rate of at least 620ksps –
below this the feature w ill not w ork due to the nature of the processing in the
demodulator.)
The user can adjust the reference level for the graph (i.e. the amplitude offset that
appears at the top of the graph) and the amplitude resolution.
A High Definition setting is available by checking the tick box w ithin the Spectrum graph.
This provides four times the resolution, giving more detail w ithin the spectral content. A
persistence mode is also available. In this mode, successive spectrums are never deleted
but left to build up a picture over time of all the received frequency information. This is
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