Spectrum Analyzer Measurements

Introduction:

In the intricate realm of spectrum analysis, selecting the right tools and understanding their nuances is paramount for accurate and efficient measurements. This guide explores essential considerations when utilizing a spectrum analyzer, delving into key parameters such as frequency range, phase noise, dynamic range, and power accuracy. Our focus shifts to the critical aspects of measurement speed, where the delicate balance between resolution bandwidth and frequency span plays a pivotal role. Join us as we unravel the complexities of spectrum analysis, providing insights into optimizing measurements for diverse applications.

Choosing the Right Spectrum Analyzer: Frequency Range and Considerations

• Frequency range (e.g. 10Mhz to 8GHz)
• Phase noise (e.g.: -120dBc/Hz)
• Maximum input power (e.g.: 0dBm)
• Dynamic range (Power levels e.g.:-174dBm to 0dBm)
• Power accuracy (e.g.:+/-0.5dB)
• Analysis bandwidth (e.g.: 100MHz)
• Resolution bandwidth (e.g.:1Hz to 10MHz)
• Modulation analysis (e.g.: LTE, Wi-Fi, GSM spectrum, analysis)

When selecting a spectrum analyzer for your measurements, the first critical characteristic to consider is the frequency range. Ensure that the chosen analyzer covers the specific frequency range of interest. For instance, if you are measuring harmonics and have a 2GHz signal, it’s advisable to choose an analyzer that spans from 2GHz to at least 8GHz. This ensures comprehensive coverage for accurate measurements across different frequencies.

Phase noise is a crucial factor in spectrum analysis, and it’s essential to aim for the lowest possible levels.

Additionally, considering the maximum input power is important, as it determines the upper limit of power that the analyzer can handle. While placing an attenuator can adjust input power, be mindful of the analyzer’s maximum input power, which is often around 30dBm. Achieving the right balance between phase noise and maximum input power enhances the accuracy and reliability of your measurements.

Dynamic range in a spectrum analyzer involves two aspects: measuring signals and small signal analysis. For accurate signal measurements, the dynamic range considers the reference power and noise floor. Simultaneously, when measuring small signals, the goal is to approach the noise floor as closely as possible.

Power accuracy is another critical consideration, with higher accuracy contributing to more reliable results. While a 0.5dB accuracy is common, opting for analyzers with even greater precision, such as 0.2dB, can be beneficial for certain applications.

As technology advances, vector signal analyzers are increasingly replacing traditional spectrum analyzers. Vector signal analyzers excel in more complex analyses, including modulation analysis for technologies like LTE, Wi-Fi, and GSM. The analysis bandwidth, typically specified in megahertz, plays a crucial role in accommodating diverse signal types. However, it’s important to note that the analysis bandwidth limitation can impact specific measurements, such as spectrum emission masks, where a broader bandwidth may be required to accurately assess adjacent channels.

Resolution bandwidth is a key factor influencing the speed and precision of a spectrum analyzer. Striking a balance between low- and high-resolution bandwidth is ideal. A high resolution bandwidth allows the analyzer to operate swiftly, while a low resolution bandwidth enhances the ability to differentiate between signals. This distinction is crucial when dealing with crowded frequency spectra, enabling the analyzer to provide detailed insights into individual signals and their characteristics.

Optimizing Measurement Speed in Spectrum Analysis

Efficient measurement speed is crucial in spectrum analysis, and achieving it involves a careful balance between two key factors: resolution bandwidth (RBW) and frequency span. The resolution bandwidth, denoted as RBW, plays a significant role in determining the speed of measurements. Simultaneously, the frequency span, influenced by settings, can either enhance or reduce measurement speed. Striking the right balance between these factors is essential, and it often involves trade-offs.

As a user conducting tests or measurements with a spectrum analyzer, understanding when to use a high- or low-resolution bandwidth is pivotal. Opting for a wide resolution bandwidth can significantly boost measurement speed but may come at the cost of reduced resolution. This trade-off requires consideration based on the specific requirements of the analysis. Similarly, adjusting the frequency span to be narrow or wide impacts the speed of measurements, offering flexibility but necessitating thoughtful decisions based on the characteristics of the signals under examination.

In summary, achieving optimal measurement speed involves a thoughtful assessment of the trade-offs associated with resolution bandwidth and frequency span. A careful consideration of these factors ensures that spectrum analysis is not only efficient but also tailored to the specific needs of the measurements being conducted.

In the visual representation above, two distinct frequency components, denoted as f1 and f2, are subjects of measurement. The choice of resolution bandwidth (RBW) significantly influences the accuracy of these measurements. With a wider RBW, the spectrum analyzer captures a broader span, potentially conflating the power levels of both frequency components. This happens because the measurement encompasses the entire section, making it challenging to differentiate between f1 and f2. While this broader measurement provides faster results, it may not be ideal for applications requiring precise distinction.

Narrowing the RBW becomes crucial when differentiation between individual frequency components is necessary. A narrower RBW allows for a more accurate measurement of the power levels of both f1 and f2. However, this increased precision comes at the expense of longer test times. Thus, selecting the appropriate RBW involves a trade-off between measurement speed and accuracy, dependent on the specific needs of the analysis.

The frequency span is another critical parameter that influences measurement outcomes. The number of frequency points within the span impacts the granularity of the measurements. Adjusting the frequency span, while maintaining the same number of points, allows for flexibility in managing the trade-off between accuracy and the speed of measurements. Depending on the characteristics of the signal under examination, a balance must be struck between a wide frequency span for broader coverage and a narrow span for detailed analysis.

Channel power measurement emerges as a key aspect in spectrum analysis, particularly for fundamental frequencies. While continuous wave (CW) measurements are common, channel power measurements offer a more intricate analysis. Spectrum analyzers are equipped to handle these complex measurements, providing a comprehensive tool for evaluating the power distribution across different frequency components. Understanding the interplay of resolution bandwidth, frequency span, and specific measurement requirements is essential for optimizing the performance of a spectrum analyzer in diverse scenarios.

Conclusion:

As we conclude our exploration into spectrum analysis, it becomes evident that achieving optimal measurements is a delicate art. The careful consideration of parameters such as frequency range, phase noise, and dynamic range sets the foundation for accurate results. In the realm of measurement speed, the interplay between resolution bandwidth and frequency span requires a thoughtful approach, balancing the need for speed with the precision of analysis. Whether distinguishing between frequency components or assessing channel power, a spectrum analyzer proves to be a versatile tool, capable of intricate measurements. With this comprehensive guide, we hope to empower users to navigate the complexities of spectrum analysis, ensuring that each measurement is a step closer to unravelling the mysteries of the RF spectrum.

Learn more about this topic by taking the complete course ‘Introduction to RF Testing Fundamentals and RF Test Architecture – RAHRF412’. Watch the course videos for more detailed understanding. Also checkout other courses on RF system and IC design on https://rahsoft.com/courses/. Rahsoft also provides a certificate on Radio Frequency. All the courses offer step by step approach.