There are spectrum analyzers for different types of signals, but this article will focus mainly on Radio Frequency (RF) Spectrum Analyzers.
What is an RF Spectrum Analyzer?
An RF Spectrum Analyzer is a widely used test instrument that measures the power of the spectrum of the input signal by measuring its amplitude, displayed on the vertical axis (y-axis), versus its frequency, displayed on the horizontal axis (x-axis). The output is displayed in the frequency domain. It’s effective in providing insights into the RF performance of circuits’ modules or systems because, with the signal information obtained from the analyzer, the type of signals present can be identified, and their frequencies, frequency levels, and amplitude can be measured. Furthermore, other spectral components of a signal, such as dominant frequency, power, distortion, harmonics, and bandwidth, can be observed.
What are the Types of Spectrum Analyzer?
Generally, spectrum analyzers are categorized into two types: the swept-tuned spectrum analyzer and the FFT spectrum analyzer. However, spectrum analyzers evolved in different form factors over the years, continually advancing with technology. Regardless of its form factors, it still serves its main purpose – to analyze the frequency spectrum of any given signal. Below are the different types and form factors of spectrum analyzers, each intended for different uses and applications.
Swept spectrum analyzer. Also known as the superheterodyne spectrum analyzer, the swept type is the traditional and the oldest form of the spectrum analyzer. The older models rely on analog techniques and have served as the foundation of spectrum analysis testing for many years. Most of these models are already outdated and are replaced by modern types of swept spectrum analyzers that use digital techniques.
Digital FFT (Fast Fourier Transform) spectrum analyzer. As the name indicates, this type of spectrum analyzer is using digital technology, converting analog signals to their digital format using FFT techniques. In a nutshell, FFT techniques use a mathematical process to transform a waveform into the components of its frequency spectrum.
Real-time spectrum analyzer. This FFT-based spectrum analyzer is a hybrid of swept and FFT type. Using the superheterodyne technique, it first converts the signal down to a lower frequency, then uses FFT techniques to analyze the signal. The manipulation of FFTs is undertaken rapidly in real-time leaving no gaps and information missed in the calculated RF spectrum. Furthermore, this type of spectrum analyzer can sample incoming signals in a time domain (as with an oscilloscope) and convert them to a frequency domain using the FFT algorithm. It captures a whole band of frequencies at once, analyses it, and then displays the spectrum.
PXI spectrum analyzer. PXI is a standard based on PCI eXtension Instrumentation and is widely used for test instrumentation, data acquisition, and control. As the name suggests, this type of spectrum analyzer is based on the PXI standard, thus, it can be incorporated into a PXI rack.
USB spectrum analyzer. This type of spectrum analyzer uses spectrum analyzer software to analyze, store, display, and replay the data. The software is installed in a computer where the device is connected to via USB port. This is more portable and cost-effective than bench-top spectrum analyzers since only the acquisition hardware needs to be purchased.
Handheld spectrum analyzer. This comes in handy in the field for monitoring radio or wireless transmissions and for checking the characteristics of the spectrum. Made in small, handheld formats, this type of spectrum analyzer does not have the same performance and capability as the larger types of a spectrum analyzer.
Networked spectrum analyzer. This type of spectrum analyzer is connected to a network via the ethernet port. It monitors devices across a network. This is useful in monitoring geographically-distributed devices and is normally installed in clusters to cover the whole geography of the devices to be monitored, thus, the larger the geography, the more spectrum analyzers are needed.
What is Spectrum Analyzers used for?
Spectrum analyzers are mainly used in electronics laboratories for testing and verifying RF performance. They are mainly utilized in RF design, general electronic circuit design, electronics manufacturing, base service and repair, and field installation and service.[1]
General tasks that spectrum analyzers are used for in a laboratory are:
- checking if a modulated signal can cause interference
- checking for the presence of noise or distortion
- checking if the signal is in the right band of frequency
- investigating general problems with a signal
- measuring power
- measuring phase noise on a signal
- measuring frequency
- undertaking EMI & EMI measurements
- plotting the level of different frequencies relative to each other
Outside the laboratory, spectrum analyzers also have many practical uses such as debugging wireless networks, testing modulation/encoding techniques, monitoring radio signals, and checking antenna performance, RF amplifier gain, signal bandwidth, and band usage. In the area of mobile networks, for example, it is extremely useful in locating and eliminating interference. Handheld spectrum analyzers, in particular, are used by mobile network operators for interference hunting to help them establish and maintain network signals.
It also has uses in other fields of science such as astronomy, geology, and biochemistry, among others. As an example, spectrum analyzers are used to analyze the chemical composition of materials based on the spectral pattern of light in the field of spectrometry.
Although a spectrum analyzer has many uses, it is not a tool for everyone. It would take a professional who understands how it works and how to interpret the characteristics of a signal to operate the device. Nonetheless, it is an indispensable test instrument that has a wide array of uses, not only in the field of electronics but also in other fields of science.
Sources:
[1] “What is a Spectrum Analyzer: RF spectrum analyzer”, N.d., https://www.electronics-notes.com/articles/test-methods/spectrum-analyzer/spectrum-analyser-overview.php Accessed December 19, 2020
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