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Home > Mall Dynamic > What Is The Spectrum Analyzer Product Application Scope And Principle
Wireless and broadcasting technologies are evolving rapidly, and many of the latest achievements have been widely integrated into the daily lives of most people. Spectrum analyzers play a vital role in the detailed measurement, analysis and evaluation of RF signals. The emergence of new applications in the field of wireless technology puts forward higher requirements on the functional level and performance of spectrum analyzer, but also increases the complexity. Therefore, spectrum analyzers must continue to evolve to meet the needs of engineers.
Spectrum analyzer is widely used in RF field. The most basic function of a spectrometer is to find and measure the amplitude of a signal. The spectrum analyzer can display the RF signal within the set frequency range in a graphical way, the stronger the signal, the larger the spectrum analyzer display amplitude. Through this characteristic, the spectrometer is used to search and find RF signals in a certain frequency band, which is widely used in the monitoring of electromagnetic environment, radio spectrum monitoring, electromagnetic compatibility measurement of electronic products, radio transmitter transmission characteristics, signal source output signal quality, anti-wireless bugs and other fields. The spectrometer can measure many characteristic parameters of RF signal, including frequency, frequency selection power, bandwidth, adjacent channel power, modulation waveform, field strength, etc. In the frequency measurement of radio frequency signals, although the frequency meter is a professional equipment, when it comes to time division multiple access signals (GSM mobile phones, IDEN, TETRA signals), frequency-hopping signals, broadband signals, ordinary frequency meters can not accurately count, power meters can not be measured in time, and spectrum meters due to high-speed signal capture, And you have a chance to measure those signals. In view of these common unstable signals, many middle and high-end spectrometers have also been optimized on the measurement software to provide dedicated automatic measurement tools.
Because the spectrometer has the ability to graphically visualize the RF signal, the spectrogram can help us understand the characteristics and types of signals, which can help us ultimately understand the modulation mode of the signal and the type of transmitter. In the military field, spectrometers are widely used in electronic countermeasures and spectrum monitoring, and different types of radar signals, communication radio signals, transponder signals, and "friend or foe" identifiers have their own spectral graphs with different characteristics. In the field of civil radio management, through the spectrogram, we can detect the illegal use of frequencies in time, which is much more efficient than traditional scanning monitoring. In the location of unknown interference sources, the spectrogram helps to determine the type of interference signal and infer the possible equipment that generates the interference signal to narrow the scope of investigation. The spectrometer is also a very good field intensity instrument, with relatively large dynamics, some with automatic measurement function of the spectrometer can easily read the field intensity value of the target signal, and can display the situation around the target frequency. In practical applications, there are many hand-held spectrometers instead of field intensity meters.
If the input of spectrum analyzer is too high, the analyzer will make it produce nonlinear distortion, and the test result will produce error due to distortion. If the signal level is too low, the signal may be masked by the bottom noise of the analyzer and the signal cannot be measured correctly, both of which reduce the dynamic range of the measurement. Therefore, it is necessary to understand the input range of the signal very clearly before use, and correctly select the input attenuation. When the radio frequency signal is input, it should also be noted that the cable characteristic impedance matches the instrument input impedance, otherwise the signal mismatch will cause attenuation, resulting in measurement errors. In the cable TV system, the cable characteristic impedance is generally 75Ω, and the analyzer input impedance can generally be selected between 50Ω and 75Ω, so the input impedance of the analyzer should be correctly selected during measurement to reduce the measurement error.
In the spectrum analyzer, the frequency resolution is a very important concept, it is determined by the bandwidth of the intermediate frequency filter, this bandwidth determines the resolution bandwidth of the instrument BWRES, if the bandwidth of the filter is 100Hz, then the spectral line frequency has 100Hz uncertainty. If there are two spectral lines in the bandwidth frequency range of a filter, it is not possible to detect that the two spectral lines are different frequency components, but its energy in the frequency range will be measured without considering how many spectral lines produce this energy, so for two closely related spectral lines, its resolution depends on the width of the filter. In the actual measurement process, the size of the frequency resolution bandwidth should be correctly selected, neither the unwanted signal can be mixed into the measurement signal, nor the required signal can be excluded.
The signal detector in the spectrum analyzer has peak detection and sampling detection, and the peak detection is commonly used. The output of the IF filter is connected to the detector, which generates a DC level proportional to the AC signal level of the IF stage output. We can choose different detection methods according to the different signal measurement indicators, such as peak detection when measuring signal electrical level, sampling detection when measuring noise.
In the spectrum analyzer, due to the large change in signal level, the logarithmic scale is generally used, and there is a logarithmic amplifier before the detector, the logarithmic amplifier compresses the signal level according to the logarithmic function, that is, for the input level amplitude V, the output voltage amplitude is lgV, which greatly reduces the signal level change detected by the detector. At the same time, the user is calibrated to a logarithmic vertical scale in decibels. In addition, the linear vertical scale can also be selected according to the different signals, which indicates a small signal range.
A video filter is a low-pass filter that reduces the noise variation in the detector output, reveals some signals that have been masked and are close to the background noise, and also helps stabilize the measurement if the noise is to be measured. When the broadband video filter is used, the noise fluctuates greatly. When narrowband video filter is used, the fluctuation is reduced significantly, the average noise of the two is the same, but the noise fluctuation is different. Therefore, we can choose the bandwidth of the video filter according to the type of test signal, for example, when the test signal is only a noisy signal, the narrowband video filter can smooth the fluctuations of these noisy signals, if the broadband video filter is selected, the measurement will change due to the influence of noise.
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