How Does a Spectrum Analyzer Work

A spectrum analyzer is a powerful tool used to measure the magnitude of an input signal versus frequency within the full frequency range of the instrument. It is widely utilized across various industries such as telecommunications, defense, satellite communications, broadcasting, aerospace, and medical research to analyze and debug various signal-related issues.

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• Telecommunications to measure the performance of cellular networks and debug wireless communications.
• The defense industry to test radar systems and detect hostile emitters.
• Satellite communications to evaluate link quality and monitor interference.
• Broadcasting to ensure compliance with regulations and optimize transmitter performance.
• The aerospace industry to test aircraft avionics and ground-based radar systems.
• Medical research to study brain waves and investigate the effects of electromagnetic radiation.

Understanding the Function of Spectrum Analyzers

Spectrum Analyzers vs. Oscilloscopes

For engineers learning about spectrum analyzers, another piece of test equipment often used in conjunction with them is an oscilloscope. Using both tools together provides a comprehensive picture of a signal. Spectrum analyzers measure the amplitude of a signal as a function of frequency, while oscilloscopes measure a signal's voltage over time. This dual approach helps in optimizing RF transmitters by assessing both power spectral density and waveform.

Noise and Spurious Signals

These analyzers are highly efficient at detecting and measuring noise and spurious signals. Signal noise is any unwanted signal present in a system, while spurious signals are unintended signals. By analyzing the frequency spectrum, a spectrum analyzer produces a graph showing the signal's amplitude versus frequency, helping to isolate and remove unwanted components, thus ensuring accurate measurements.

Choosing a Real-Time Spectrum Analyzer

There are two types of spectrum analyzers: swept and real-time. Swept analyzers sweep the frequency span between start and stop frequencies, then analyze and display the information. However, the delay between sweeps can miss intermittent captures. Real-time spectrum analyzers capture and display frequency information almost instantaneously, making them ideal for capturing pulsating or intermittent signals.

Benefits of Real-Time Acquisition

Real-time spectrum analyzers can capture brief intermittent signals, making them perfect for observing modulated wireless or digital signals and EMI troubleshooting. For example, in the 2.4 GHz ISM band, these analyzers can clearly show Wi-Fi and Bluetooth signals.

USB-Controlled Real-Time Analyzers

Low-cost USB-controlled options like the Tektronix RSA306B or Signal Hound BB60C offer feature-rich PC software. The EMCVu software package is highly recommended for pre-compliance testing. Both analyzers are compact and fit nicely into an EMC troubleshooting case.

Signal Hound BB60C Spectrum Analyzer

The Signal Hound BB60C real-time spectrum analyzer can tune from 9 kHz to 6 GHz. It offers up to 27 MHz instantaneous bandwidth and can display frequency information in near real-time. A powerful PC is needed for processing the signal data.

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Tektronix RSA306B Spectrum Analyzer

The RSA306B, powered solely through a USB 3.0 port, can measure from 9 kHz to 6.2 GHz. This analyzer is highly useful for EMI pre-compliance testing and interference hunting with its 40 MHz real-time bandwidth.

Siglent SSA3075X-R and Rigol RSA5000 Real-Time Spectrum Analyzers

Rigol and Siglent Technologies offer affordable real-time spectrum analyzers suitable for EMC troubleshooting and pre-compliance work. Both the Rigol RSA5000 series and Siglent SSA3075X-R series provide fast acquisition and clear display features necessary for capturing dynamic signals.

Example Measurements

Embedded Processor

Using an H-field probe, we measured the emission profile of an embedded processor. In real-time mode, both narrow band and broadband EMI components were observable.

Motor Noise

Measuring harmonic cable currents from a demo board attached to a PWM-controlled motor showed how real-time analysis can reveal transient or overlapping emissions, aiding in effective EMI troubleshooting.

Conclusion

Real-time spectrum analyzers are essential for detecting intermittent signals, interference hunting, and analyzing wireless/digital modulations. They provide a comprehensive solution for pre-compliance testing and EMI troubleshooting. High-quality, affordable options from manufacturers such as Tektronix and Signal Hound are recommended for any serious electromagnetic testing needs.

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