Span Considerations (W-CDMA(3GPP)/HSPA)

When selecting a Frequency Span, select the narrowest span that includes all of your signal components (a span that is slightly larger than the bandwidth of your signal). If a span that is too narrow is selected, your measurement may have excessive errors or the VSA may lose carrier lock. If the span is less than (1+filter alpha)*chip rate, the VSA shows DATA? to indicate that the results may not be accurate.

For best results, the Frequency Span should be set according to the following formula (filteralpha is the filter characteristic of the Nyquist filter used to demodulate the W-CDMA Code Division Multiple Access: One of several digital wireless transmission methods in which signals are encoded using a specific pseudo-random sequence, or code, to define a communication channel. A receiver, knowing the code, can use it to decode the received signal in the presence of other signals in the channel. This is one of several "spread spectrum" techniques, which allows multiple users to share the same radio frequency spectrum by assigning each active user an unique code. CDMA offers improved spectral efficiency over analog transmission in that it allows for greater frequency reuse. Other characteristics of CDMA systems reduce dropped calls, increase battery life and offer more secure transmission. See also IS-95. signal):

Frequency Span ³ (1 + Filter alpha) * Chip Rate

If a span that is too wide is selected, your measurement may be affected by excessive noise and slower speed. The demodulator can be turned OFF (MeasSetup > Measurement Type > Demod Off) and the span set while viewing the spectrum of your signal.

Using the Preset to Standard configuration settings will select a default span that should work well.

The following topics may help optimize your measurements and explain the reasons for changes made automatically by the VSA:

Display Limitations

Resolution Bandwidth

Measurement Speed Considerations

See Also

Setting up a W-CDMA(3GPP) Measurement

About Measurement Interval and Offset