Table of Contents
Advertisement
Example 1: Resolving Closely Spaced Signals (with Resolution Bandwidth)
Example 1: Resolving Closely Spaced Signals
(with Resolution Bandwidth)
What Is Resolution Bandwidth?
Signal resolution is determined by the intermediate frequency (IF)
filter bandwidth. The spectrum analyzer traces the shape of its IF filter
as it tunes past a signal. Thus, if two equal-amplitude signals are close
enough in frequency, the filter shapes for the two signals can fall on top
of one another and appear as a single response. If two signals are not
equal in amplitude but are still close together, the smaller signal can be
hidden under the response of the larger one.
Spectrum Analyzer Function Used
The resolution bandwidth function (RES BW) selects the appropriate IF
bandwidth for a measurement. (Agilent Technologies specifies
resolution bandwidth as the 3 dB bandwidth of a filter.) The following
guidelines can help you determine the appropriate resolution
bandwidth to choose.
Stepping Through a Measurement of Two Equal
Amplitude Signals
Generally, to resolve two signals of equal amplitude, the resolution
bandwidth must be less than or equal to the frequency separation of the
two signals. For example, to resolve two signals of equal amplitude with
a frequency separation of 1 kHz, a resolution bandwidth of 1 kHz or less
should be used.
1. Connect two signal sources to the spectrum analyzer INPUT 50 Ω.
Set the frequency of one source to 499.5 kHz and the other source to
500.5 kHz. Set both sources to the same amplitude.
2. Press
on the spectrum analyzer to start the procedure from
PRESET
a preset state, and set the spectrum analyzer center frequency to 500
kHz.
3. Set the span to 10 kHz.
4. Set the resolution bandwidth to 1 kHz. See Figure 2-1.
5. Change the resolution bandwidth to a wider value and notice that
you can no longer see that there are two signals present.
6. Change the two source frequencies to 499 kHz and 501 kHz.
Chapter 2
Making Measurements
51
Advertisement
Table of Contents
