Spectrum analysers, also known as oscilloscopes, are professional measuring devices for diagnosing the frequencies present in a signal. They are used in many telecommunications, scientific and counter-surveillance fields. We explain their complex operation and why they are so effective
What is a spectrum analyser?
Although the oscilloscope is quite a popular device in many fields, such as telecommunications, counter-surveillance, electronics or acoustics, a lot of people are not familiar with its actual use and how it works. A spectrum analyser is a professional piece of equipment responsible for measuring and analysing signals in a given frequency range.
Simply put, this device allows you to see on a graph whether low or high tones are visible in the signal under investigation. In practice, spectrum analysis determines what signals are present at a given frequency amplitude and what power they have.
We will illustrate this as follows: imagine that you have a radio transmitter that peels off different stations. Spectrum analysers allow you to see them all at once. Each frequency is a different station, and the height of the bar on the spectrum analyser’s display shows how strong the signal from that station is.
Of course, in reality, an oscilloscope can work over a much wider range of frequencies and analyse signals far more complex than radio, such as Wi-Fi signals, Bluetooth or electromagnetic interference. However, for a general understanding of the principle of operation – dividing a signal into different frequencies and measuring their power – the analogy with a radio well captures the essence of how this device works.
What are spectrum analysers used for?
The specification of this type of equipment, often equated with spectrum analysers, means that they can be used for a wide variety of tasks.
Most commonly, spectrum analysers are used in the telecommunications industry. Engineers use them to test transceiver equipment such as 5G, LTE, Wi-Fi or satellite systems. These analysers allow them to measure signal levels, detect interference or diagnose transmission quality. In addition, they enable the detection of interference to RF signals.
Spectrum analyser functions: signal analysis and other applications
Oscilloscopes have many applications in various fields.
The most common of these are:
- RF and microwave signal diagnostics,
- analysis of acoustic signals,
- calibration of electronic devices,
- laboratory and scientific research,
- detection of eavesdropping and other surveillance devices.
Spectrum analysers are used by workers in many sectors. The specification of the devices makes them suitable for many situations and conditions. Due to their versatility, spectrum analysers remain the standard for diagnosis and testing of signal systems.
Who uses spectrum analysers? Invaluable help in many environments

Spectrum analysers are widely used in a variety of industries, by professionals involved in signal analysis, both commercially and in research:
- telecommunications: equipment testing, optimisation of mobile and wireless networks, RF interference detection;
- electronics: quality control and device performance analysis;
- military and defence: detection of hostile systems, verification of security effectiveness;
- acoustics and sound engineering: testing the sound properties of audio devices, optimising sounds;
- scientific research: analysing waves from various physical processes;
- transport: exploration of navigation and communication systems;
- detectives: spectrum analysers are extremely effective devices for detecting eavesdropping.
Spectrum analysers are therefore a key tool for a wide range of professionals. Their versatility and precision make them suitable wherever analysis of streams in the frequency domain is required.
Types of spectrum analysers: testing and monitoring of different frequencies, interference detection
There are different types of spectrum analysers, each of which is used in different areas of technology and science. Analysers are divided up, among other things, according to the technology used and the shape and size. They can be divided, for example, into laboratory, handheld or portable devices.
One basic type is analysers based on bandpass filters. In such devices, waves pass through a set of filters that sweep only specific frequency ranges, allowing detailed examination of individual signal components.
Another important type is analysers based on the superheterodyne principle. These use frequency conversion – the input stream is first mixed with a signal at a known heterodyne frequency, allowing it to be shifted to an intermediate frequency that is easier to analyse. This type of analyser is widely used in telecommunications and microwave measurements.
Modern spectrum analysers based on the Fast Fourier Transform (FFT) have become very popular . They operate fully digitally, transforming the time stream into its frequency representation using mathematical algorithms. They are often used in acoustic analysis.
In more specialised applications, such as optical analysis, spectrum analysers based on optical and acousto-optic phenomena are used . These devices make use of phenomena such as diffraction of light on diffraction gratings or the acousto-optic effect, allowing the spectrum of light or ultrasonic waves to be studied.
Real-time spectrum analysers, on the other hand, enable continuous analysis of signals, which is particularly useful for monitoring dynamically changing radio waves. They can detect short-lived interference or streams that occur over very narrow time intervals.
The choice of the specific type of equipment depends, among other things, on the required precision of the measurements, the frequency amplitude and the type of signal to be analysed.
How is the spectrum measured and analysed?

The course of detection with a spectrum analyser follows several steps. We will describe them in a very simplified way to better understand the characteristics of the process.
- Connecting the output signal
A signal source, such as an antenna, microphone or electrical cable, is connected to the receiver. This allows the device to ‘listen’ to the waves we want to study.
- Signal attenuation and filtering
The equipment reduces the strength of the stream. if it is too strong, to avoid overload. Filters also help to cut off interference from outside the frequency range being studied.
- Frequency conversion
A modulation of the stream to a different, more easily analysed frequency takes place. This facilitates further processing and more accurate measurements.
- Filtering by frequency (RBW)
The analyser separates signals of different frequencies, determining how accurately it should distinguish those lying close to each other. The narrower the filter, the more accurate the measurement.
- Signal detection (power measurement)
The device measures the waves and converts them into a voltage that can be represented on a graph. It does this in various ways, e.g. by showing only the strongest signals or by averaging the value.
- Signal to digital data conversion (FFT)
In modern analysers, the signal is converted into digital data and then analysed mathematically using an algorithm (FFT), allowing multiple frequencies to be examined simultaneously.
- Signal power level calculation
The analyser shows the signal power in decibels, which makes it easier to compare signals with different power levels, even when the differences are very large.
- Frequency sweep
The instrument examines successive frequency ranges, ‘sweeping’ through them and recording signals at different levels, creating a complete spectrum picture.
- Display of results on screen
The measurement results are displayed as a range: the horizontal axis (X) is the frequency and the vertical axis (Y) shows the signal strength. Stronger waves are represented by higher peaks.
- Operator analysis of results
The analyser operator can check whether the detected signals are as expected, find interference or detect unwanted emissions such as hidden eavesdropping devices.
With this tool, both radio and audio signals can be analysed, making it useful in telecommunications, electronics, security and many other fields.
Summary
Spectrum analysers are versatile and advanced measuring devices that are used in many industries and fields. A full understanding of their operation, as well as the ability to operate such equipment, provides access to extremely important information that cannot be obtained using other devices.
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