Module 16: Test Equipment: Advanced
This module takes you beyond the multimeter and oscilloscope into the instruments engineers use for serious measurements. A spectrum analyzer shows what is happening in the frequency domain — harmonics, spurious signals, interference and noise that an oscilloscope cannot reveal. A vector network analyzer measures how circuits, filters, cables and antennas reflect and pass signals at every frequency. Signal generators provide the known test signals all of these measurements depend on, and Q meters and time-domain reflectometers characterize components and cables.
Each of these instruments was once found only in professional laboratories costing tens of thousands of dollars. Today, capable versions cost a few hundred dollars or less, and open-source instruments such as the NanoVNA and TinySA have brought vector network analysis and spectrum analysis within reach of every hobbyist, student and small company.
- Use a spectrum analyzer to measure signal power in dBm, identify harmonics and spurious outputs, and connect safely with attenuators
- Carry out bench EMC pre-compliance measurements with a LISN and near-field probes
- Explain S-parameters and measure reflection and transmission with a VNA
- Calibrate a VNA and measure filters, components and antennas
- Read impedance on the VNA's Smith chart display
- Use function, arbitrary waveform and RF signal generators correctly, including the 50-ohm output trap
- Measure an audio amplifier's gain, response, power, distortion, noise and stability
- Measure inductor Q and self-resonance, and locate cable faults with a TDR
- Spectrum Analyzers: Introduction
- Spectrum Analyzer Controls
- Using a Spectrum Analyzer
- EMC Pre-Compliance Testing
- Vector Network Analyzers: Introduction
- S Parameters Explained
- VNA Calibration
- Measuring Filters with a VNA
- VNA Smith Chart Display
- Function and Signal Generators
- Testing an Audio Amplifier with a Signal Generator
- Q Meters and RLC Bridges
- Time Domain Reflectometers
Module Overview
The module is organized around the major instrument types. The first four lessons cover spectrum analyzers: how they differ from oscilloscopes, what each control does, how to measure safely and accurately, and how to use one for EMC pre-compliance testing — finding the emissions that would fail a product's formal tests while they are still cheap to fix.
The next five lessons cover the vector network analyzer, one of the most powerful instruments available: what it measures, what S-parameters mean, how calibration removes the effects of cables and adapters, how to characterize filters, and how to read the Smith chart display.
The final four lessons cover signal generators and their use in testing an audio amplifier from end to end, Q meters and RLC bridges for characterizing inductors at the frequencies where they work, and time-domain reflectometers for finding faults along cables and circuit-board traces.
The experiments and examples are designed around affordable instruments: the TinySA spectrum analyzer, the NanoVNA vector network analyzer, a low-cost DDS function generator, and a computer sound card for audio measurements.
Lessons
Spectrum Analyzers: Introduction
Spectrum Analyzers: Introduction
What a spectrum analyzer shows, dBm and dBc, swept, FFT and real-time analyzers, key specifications and affordable instruments.
Spectrum Analyzer Controls
Spectrum Analyzer Controls
Span, resolution and video bandwidth, reference level and attenuation, detectors, markers, and a complete harmonic measurement workflow.
Using a Spectrum Analyzer
Using a Spectrum Analyzer
Connecting safely with attenuators, avoiding analyzer overload, and measuring oscillators, amplifiers and modulated signals.
EMC Pre-Compliance Testing
EMC Pre-Compliance Testing
EMC standards and limits, dBµV and detectors, conducted emissions with a LISN, near-field probes, and common fixes.
Vector Network Analyzers: Introduction
Vector Network Analyzers: Introduction
What a VNA measures, scalar versus vector, key specifications, applications, and the NanoVNA.
S Parameters Explained
S Parameters Explained
S11, S21, S12 and S22 from first principles, with worked examples and an S11 to VSWR and impedance converter.
VNA Calibration
VNA Calibration
Open, short, load and through standards, the calibration plane, port extension, and keeping a calibration valid.
Measuring Filters with a VNA
Measuring Filters with a VNA
Insertion loss, bandwidth, shape factor and stopband attenuation from S21, input match from S11, and a full example.
VNA Smith Chart Display
VNA Smith Chart Display
Reading impedance on the VNA's Smith chart, following a sweep, and using the chart to design a match.
Function and Signal Generators
Function and Signal Generators
Function, arbitrary waveform and RF generators, specifications, output levels and the 50-ohm trap, sweep and burst modes.
Testing an Audio Amplifier with a Signal Generator
Testing an Audio Amplifier with a Signal Generator
Gain, frequency response, maximum power, distortion, noise, impedance and the square-wave test on an audio amplifier.
Q Meters and RLC Bridges
Q Meters and RLC Bridges
Measuring inductor Q and self-resonant frequency with Q meters, RLC bridges and a VNA.
Time Domain Reflectometers
Time Domain Reflectometers
How a TDR finds impedance changes and faults along cables and traces, and VNA-based TDR.