Appendix
R&S
®
Spectrum Rider FPH
554
User Manual 1321.1011.02 ─ 11
15
Appendix
In this appendix, additional information on how a spectrum analyzer work is given.
15.1
How a Spectrum Analyzer Works
Basically, it is possible to measure and analyze RF signals either in the time domain or
the frequency domain.
Measurements in the time domain show signal variations over time. You can perform
these with an oscilloscope, for example. Measurements in the frequency domain show
the frequency components of a signal. To perform measurements in the frequency
domain, you can use a spectrum analyzer.
Both modes are essentially equivalent because applying the Fourier transform to any
signal converts it into its spectral components. Depending on the signal characteristic
to be measured, one method is usually more appropriate than the other. With an oscil-
loscope, it is possible to tell whether a signal is a sine wave, a square wave with a cer-
tain on/off ratio or a sawtooth wave. However, detecting superimposed low-level sig-
nals or monitoring the harmonic content of the signal is easier with a spectrum or sig-
nal analyzer.
shows the theoretical basis of the two measurement methods. In the time
domain, an oscilloscope would, for example, show a section of the signal that is a
square wave. The same signal, when viewed with a spectrum analyzer, would show a
line spectrum (the fundamental and its harmonics).
Figure 15-1: Visualization of time domain and frequency domain
How a Spectrum Analyzer Works
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