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Application Note
Making Stimulus/Response Measurements
Using the Agilent N9322C Basic Spectrum Analyzer and Tracking
Generator
The tracking generator provides a cost-effective way for spectrum analyzer users
to expand their testing to cover more component-level characterization.
Introduction to Tracking Generators
A tracking generator is a signal source whose RF output follows the tuning of
the spectrum analyzer. The tracking generator output signal is generated by
mixing the signals from two or more oscillators. A simplified block diagram is
shown in Figure 1.
ATT PRE filter Mix IF filter
RF IN
DSP
Fs F if
Device Control &
LO S display
TG OUT F's F'if
S
Filter Mix LO
Figure 1. Block diagram of tracking generator
The tracking generator uses the Swept LO from the spectrum analyzer and
mixes that LO signal with a stable, fixed oscillator. If we tune the oscillator
in the tracking generator (F'if) to the center frequency of the IF filter in the
spectrum analyzer (F if), and use the difference mixing product, then the output
frequency of the tracking generator (F's) will equal the input frequency of the
spectrum analyzer (F s). The spans of the spectrum analyzer and tracking gen-
erator are matched and synchronous and therefore precise tracking is achieved.
Benefits of Using a Tracking Generator
1. It stretches your instrument budget -- One instrument provides
dual-purpose measurements.
In addition to measuring signal amplitude characteristics such as carrier power,
sidebands, and harmonics, a spectrum analyzer with a tracking generator
can also make scalar network analysis with high dynamic range, such as the
insertion loss, pass/stop band of a component, or the gain of an amplifier. For
example, adding a tracking generator to your N9322C BSA provides single-
channel scalar network analysis in addition to the analyzer's spectrum analysis
capabilities.
DUT
Figure 2. Using N9322C and its tracking generator for scalar network analysis
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2. It is effective for scalar transmission measurements --The
tracking generator output and the RF input of the spectrum
analyzer are well synchronized.
The precise tracking between the tracking generator and the analyzer estab-
lishes a well-synchronized stimulus/response measurement system. It is able
to cover scalar transmission measurements such as gain, frequency response,
insertion loss, and flatness on components and subsystems.
Device
E Incident
E
Transmitted
E Reflected
Figure 3. Transmission measurement
Differences between Network Analyzers and
Spectrum Analyzers
Network analyzer Spectrum analyzer
Measures components, devices, circuits, Measures signal amplitude characteristics
sub-assemblies
Contains source and receiver Can demodulate and measure complex
signals
Displays ratioed amplitude and phase Contains receivers only
(by frequency or power sweeps)
Offers advanced error correction Measures scalar component (no phase
information) with tracking generator or
external sources
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Introduction to the N9322C BSA and its Tracking
Generator
The Agilent N9322C BSA is a 7 GHz general purpose spectrum analyzer. It is
expandable to cover scalar transmission measurement by adding a tracking
generator (Option TG7). Option TG7 gives you the ability to make accurate scalar
transmission measurements, such as gain and insertion loss of a DUT.
N9322C Option TG7 Overview