Parameter Interactions; Span Considerations - Agilent Technologies 89410A Operator's Manual

Digital Demodulation Concepts (Opt. AYA)

Parameter interactions

Changing one parameter may necessitate changes in other parameters to achieve
the desired measurement. The following topics may help you optimize your
measurements and explain the reasons for changes made automatically by the
analyzer.

Span considerations

When selecting a frequency span, select the narrowest span that includes all of your
signal components (select a span that is larger than the bandwidth of your signal).
If you select a span that is too narrow, your measurement may have excessive
errors or the analyzer may lose carrier lock. If you select a span that is too wide,
your measurement may be affected by excessive noise and slower speed. You may
want to select the Vector instrument mode and set the span while viewing the
spectrum of your signal.
The analyzer displays a warning message if the frequency span is less than the
symbol rate. If you see this warning message, increase the frequency span until it
includes all components of your signal.
When using digital demodulation, the symbol rate determines the maximum
frequency span that you can select, as follows:
(SymbolRate)
Maximum Span = 20
1.28
This formula can be rewritten to obtain the maximum span-to-symbol-rate ratio.
++
For FSK demodulation formats, you can increase this ratio:
Maximum Span 20 Maximum Span
= = 15.625
OR
1.28
Symbol Rate Symbol Rate
++ The FSK demodulation format presents an exception because the value [ max span/symR ] in the [ configure meas memory ] menu
can be increased in value up to 100 if sufficient memory is available. This accommodates the wider spans often required by FSK
demodulation.
22 - 10