Chapter 3. Introduction

Hence, theoretically all these decomposed
components as sine wave with associated frequency,
amplitude, and phase can be investigated separately to
determine the characteristics of the desired signal. On the
other hand, we may transform all the analysis of sine
waves in time domain into the measurements in
frequency domain by using this component analysis. With
the interpretation of Fourier’s theory, one can clearly
digest what the differences of periodic signal analysis in
between time domain and frequency domain. In order to
transform the signal analysis from time domain to
frequency domain, one has to proceed in the successive
calculations and can only observe the fragmentary
behaviors of desired signal.





Using Fourier Transform allow us to bring about
more depth thinking in many aspects of signal diagnosis,
which requires a framework to evaluate each component
frequency and phase for a signal event along the entire
frequency range. For example, a square wave in time
domain being transformed into frequency domain and
then transformed back to time domain would often result
in saw tooth wave as a distortion without preserving the
exact phase.

 An Introduction to Spectrum Analyzer

wave in the frequency domain can be expressed by
amplitude and frequency. Through the spectrum as
shown, we may understand that the impure sine wave
contained a second harmonic, third harmonic, and so on.
There often consists of some critical device components
including amplifier, oscillator, mixer or filter in a RF
circuit, where their electrical behavior cannot easily
grasped only by inspecting on an oscilloscope screen.
With a spectrum analyzer, the desired frequency response
to characterize the circuit can be easily acquired.

Why to carry on a measurement with a spectrum?
In addition to the amplitude analysis in traditional
time domain, there also provides with the amplitude
measurement in frequency domain. Thus, with the
amplitude analysis, spectrum analysis is the optimal
solution to diagnose the harmonic components.
Especially for engineers involving in the harmonic
distortion for communication system, the distortion of
message modulated onto a carrier. Third-order
inter-modulation could be a significant technical
challenge as the distortion portions can lie in the band of
relevance and can be filtered out. Thus may affect the
message transmission quality around communication
systems.