Application Note
Spectrum Monitoring Techniques
Introduction
Spectrum monitoring is a powerful tool
that can be used to ensure that the RF
communications we all depend on for both
civilian and defense applications work, and
work well.
The need to make more effective use of
our RF spectrum comes from a number
of fronts.
• On the consumer side, as the move to
smart phones and 4G/5G shows, the
public appetite for bandwidth is growing
rapidly. This is driving the re-farming of
spectrum in auctions, spectrum clearing
activity, coverage checks, and inevitably,
activity by the broadcasters, who are
giving up some of this spectrum.
• Emergency services are expanding into
new bands with new technologies – P25,
new versions of TETRA, or moving to
LTE. This migration drives spectrum monitoring needs similar to the cellular needs, even if on a smaller scale.
• Defense departments around the world are becoming more and more dependent on electronic communications
– for routine messaging, tactical communications, and covert operations.
In each area, spectrum monitoring is used to ensure reliable communications. The need for effective spectrum
monitoring will only grow for the foreseeable future. This note will help you understand the tradeoffs in monitoring
spectrum, as well as how to set up your analyzer for your situation.
Using a spectrum analyzer for unattended
spectrum monitoring
Figure 1: U. S. 700 MHz band showing new uplink activity at 712 MHz.
2
Contents
Introduction ................................................................ 1
Why Monitor Spectrum?
............................................ 3
Spectrum Monitoring Techniques
.............................. 3
Signals of Interest
...................................................... 4
Setting up to Monitor Spectrum
................................. 6
Selecting a Frequency to Monitor
.......................... 6
Selecting a Span and Choosing the RBW
............. 7
Trace Modes........................................................... 8
Detectors
................................................................ 9
Video Bandwidth (VBW)
......................................... 9
Sweep Modes
....................................................... 10
Sweep Mode Summary
..................................... 11
Amplitude Trade-Offs
........................................... 11
Attenuation and Reference Level
...................... 12
Preamp
.............................................................. 12
Band-Limiting
.................................................... 12
Sweep Mode & RBW
........................................ 12
Antenna Considerations
....................................... 13
Remote Operation – Looking Ahead
.................... 14
Trace Management Strategies
................................ 14
Time Resolution.................................................... 14
Save-on-Event
...................................................... 15
Save-on-Event Tradeoffs
................................... 16
Spectrogram Record Mode
.................................. 16
Length of Time
.................................................. 16
Spectrogram Recording Tradeoffs
.................... 17
How to Set Up a Spectrogram Recording
......... 17
Expanding Spectrum Monitoring Capability
............ 18
Channel Scanner
.................................................. 18
Zero Span Measurements
.................................... 18
Analog Signal Demodulation
................................ 19
Spurious Emission Measurement......................... 20
easyTest Tools
...................................................... 21
Spectrum Analyzer Remote Control
........................ 22
Web Remote Control
............................................ 22
Signal Location
........................................................ 23
Selecting a Spectrum Monitoring Tool
..................... 23
Third Order Intercept (TOI)
.................................. 23
Phase Noise
......................................................... 23
DANL
.................................................................... 23
Dynamic Range
.................................................... 24
Overload Indicator
................................................ 24
Multi-step Attenuator
............................................ 24
Preamplifier
.......................................................... 24
Burst Detect
.......................................................... 24
Video Bandwidth Control
...................................... 25
User Interface
....................................................... 25
Field Strength Measurements
.............................. 25
Spectrum Recording
............................................. 25
Conclusion
............................................................... 26