Span Considerations (1xEV-DO)
When selecting a frequency span, select the narrowest span that includes all of your signal components (select a span that is slightly larger than the bandwidth of your signal). If a span that is too narrow is selected, the measurement may have excessive errors or the VSA may lose carrier lock. If the span is less than 1.024 ´ chip rate, the VSA shows "NO DATA?" to indicate that the results may not be accurate.
For best results, the frequency span should be set according to the following formula (filter_alpha is the filter characteristic of the Nyquist filter used to demodulate the 1xEV-DO signal):
Frequency Span ³ 1.024 ´ Chip Rate
If a span that is too wide is selected, the measurement may be affected by excessive noise and slower speed. The demodulator may need to be turned off (click ) and the span set while viewing the spectrum of the signal.
Using the Preset to Default configuration settings will select a default span that should work well.
The following topics may help optimize measurements and explain the reasons for changes made automatically by the VSA.
See Also
