Chapter 5
Spectrum Analyzer
Measurements
Introduction
This chapter provides a description of Spectrum Analyzer measurements and procedures
when the Site Master S332D is in Spectrum Analyzer Mode.
Measurement Fundamentals
Measurement fundamentals include the use of additional spectrum analyzer functions be-
yond frequency, span, amplitude and marker functions. In particular, this section focuses
on resolution bandwidth, video bandwidth, sweep, and attenuator functions.
Effect of Resolution Bandwidth
Resolution Bandwidth 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. If more than
one IF filter is used in a spectrum analyzer, the narrowest one dominates and is considered
the resolution bandwidth.
The choice of resolution bandwidth depends on several factors. Filters take time to settle.
That is, when a signal first appears at the input of the filter, it will take a while before the
signal appears at the output. Additionally, the output of the filter will take some time to set-
tle to the correct value, so that it can be measured. The narrower the filter bandwidth (reso-
lution bandwidth) the longer the settling time.
The choice of resolution bandwidth will depend on the signal being measured. If two
closely-spaced signals are to be measured individually, then a narrow bandwidth is re-
quired. If a wider bandwidth is used, then the energy of both signals will be included in the
measurement. Thus, the wider bandwidth does not have the ability to look at frequencies se-
lectively but instead simultaneously measures all signals falling within the resolution band-
width.
Therefore, a broadband measurement would aggregate all signals and noise within the mea-
surement bandwidth into a single measurement. On the other hand a narrow-band measure-
ment will separate the frequency components, resulting in a measurement that includes
separate peaks for each signal. There are advantages to each. The ultimate decision will be
dependent on the type of measurement required by the user.
There is always some amount of noise present in a measurement. Noise is often broadband
in nature; that is, it exists at a broad range of frequencies. If the noise is included in the
measurement, the measured value will be in error (too large) depending on the noise level.
5-1