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Technical Indicators of Spectrum Analyzer

2019-03-08 14:45:49 RPG Electronics (Shenzhen) Co., Ltd. 7

1) Input frequency range

Refers to the maximum frequency range in which the spectrum analyzer can work normally. The upper and lower limits of the range are represented by HZ, which is determined by the frequency range of the scanning local oscillator. The frequency range of modern spectrum analyzers can usually range from low frequency bands to radio frequency segments, even microwave segments, such as 1 kHz to 4 GHz. The frequency here refers to the center frequency, which is the frequency at the center of the display spectrum width.

(2) Resolution bandwidth

Refers to the minimum spectral line spacing between two adjacent components in the resolved spectrum, in HZ. It means that the spectrum analyzer is capable of distinguishing two equal-amplitude signals that are close together to each other at a specified low point. The spectrum of the signal under test seen on the spectrum analyzer screen is actually a dynamic amplitude-frequency characteristic of a narrow-band filter (like a bell curve), so the resolution depends on the bandwidth of this amplitude-frequency. The 3dB bandwidth defining the amplitude-frequency characteristics of this narrow-band filter is the resolution bandwidth of the spectrum analyzer.

(3) Sensitivity

Refers to the ability of the spectrum analyzer to display the minimum signal level given a resolution bandwidth, display mode, and other influencing factors, expressed in units of dBm, dBu, dBv, V, etc. The sensitivity of the superheterodyne spectrum analyzer depends on the internal noise of the instrument. When measuring small signals, the signal lines are displayed above the noise spectrum. In order to easily see the signal line from the noise spectrum, the general signal level should be 10 dB higher than the internal noise level. In addition, the sensitivity is also related to the sweep speed, the sweep speed is fast, and the lower the peak of the dynamic amplitude frequency characteristic, the lower the sensitivity and the difference in amplitude.

(4) Dynamic range

Refers to the maximum difference between two signals that appear simultaneously at the input with the specified accuracy. The upper limit of the dynamic range is loved by the constraints of nonlinear distortion. There are two ways to display the amplitude of the spectrum analyzer: linear logarithm. The advantage of the logarithmic display is that a large dynamic range is obtained over a limited range of effective screen heights. The dynamic range of the spectrum analyzer is generally above 60dB, and sometimes even above 100dB.

(5) Frequency scan width (Span)

Another analysis of spectrum width, span, frequency range, spectrum span and other different names. Usually refers to the frequency range (spectral width) of the response signal that can be displayed in the leftmost and right vertical tick marks of the spectrum display. Automatically adjusted according to the test needs, or artificial settings. The scan width indicates the range of frequencies displayed by the analyzer during a measurement (ie, a single frequency sweep) that can be less than or equal to the input frequency range. The spectrum width is usually divided into three modes.

1 Full Sweep The spectrum analyzer scans its effective frequency range at a time.

2 Sweep per division The spectrum analyzer scans only one specified frequency range at a time. The width of the spectrum represented by each cell can be changed.

3 zero sweep frequency width is zero, the spectrum analyzer does not sweep, becomes a tuned receiver.

(6) Scan time (simply ST)

That is, the time required to perform a full frequency range scan and complete the measurement, also called the analysis time. Usually, the shorter the scan time, the better, but to ensure measurement accuracy, the scan time must be appropriate. The factors related to scan time mainly include frequency sweep range, resolution bandwidth, and video filtering. Modern spectrum analyzers typically have multiple scan times to choose from, and the minimum scan time is determined by the circuit response time of the measurement channel.

(7) Amplitude measurement accuracy

There are absolute amplitude accuracy and relative amplitude accuracy, which are determined by many factors. Absolute amplitude accuracy is an indicator for the full-scale signal, which is affected by the input attenuation, IF gain, resolution bandwidth, scale fidelity, frequency response and the accuracy of the calibration signal itself. The relative amplitude accuracy is related to the measurement method. There are only two sources of error in the frequency response and calibration signal accuracy, and the measurement accuracy can be very high. The instrument is calibrated before leaving the factory, and various errors have been recorded and used to correct the measured data. The displayed amplitude accuracy has been improved.


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