Abstract: Spectrum analyzers are common tools used by electronic engineers on workstations or in university laboratories. In this article, we have sorted out six common questions about the use of spectrum analyzers and hope that it will answer your questions.
Q1: How to set the best sensitivity of the spectrum analyzer to facilitate observation of small signal A: firstly set the corresponding center frequency, span (SPAN) and reference level according to the size of the small signal to be measured; then there is no If the signal-to-noise ratio of the small signal to be measured is less than 15dB, the RBW is gradually reduced. The smaller the RBW is, the lower the noise floor of the spectrum analyzer is, and the higher the sensitivity is.
If the spectrum analyzer has a preamp, turn it on. Pre-releasing can increase the noise figure of the spectrum analyzer, thereby increasing the sensitivity. For small signals with low signal-to-noise ratio, VBW can be reduced or trajectory averaging can be used to smooth noise and reduce fluctuations.
It should be noted that the measurement result of the spectrum analyzer is the sum of the external input signal and the internal noise of the spectrum analyzer. To make the measurement result accurate, the signal-to-noise ratio is usually required to be greater than 20 dB.
Q2: The smaller the resolution bandwidth (RBW), the better?
A: The smaller the RBW, the better the spectrum analyzer sensitivity, but the scanning speed will be slower. It is best to set RBW based on actual test requirements to find a balance between sensitivity and speed – both to ensure accurate signal measurement and fast measurement speed.
Q3: How to select the average detection type: Power?Logpower?Voltage?
Logpower Logarithmic Power Average: Also called VideoAveraging, this average mode has the lowest noise floor and is suitable for low-level continuous wave signal testing. However, there is a certain error in the "like-noise" signal, such as the wide-band modulation signal W-CDMA.
Power average: Also known as RMS average, this averaging method is suitable for total power measurement of "noise-like" signals (eg, CDMA).
Voltage averaging: This averaging method is suitable for observing the rise and fall time measurements of amplitude-modulated or pulse-modulated signals.
Q4: Sweep mode selection: Sweep or FFT?
A: The sweep mode of the modern spectrum analyzer usually has Sweep mode and FFT mode. Usually in a narrow RBW setting, FFT is more speed advantage than sweep, but sweep mode is faster under wider RBW conditions.
When the span is smaller than the analysis bandwidth of the FFT, the FFT mode can measure the transient signal; when the span exceeds the FFT analysis bandwidth of the spectrum analyzer, if the FFT scan mode is used, the working method is to segment the signal, segment and segment. If there is discontinuity in time, the useful signal may be lost during the signal sampling gap, and the spectrum analysis will be distorted. This type of signal includes: pulse signals, TDMA signals, FSK modulation signals, and the like.
Q5: The influence of the detector selection on the measurement result?
Peak detection method: Select the maximum value in each bucket as the measurement value. This detection method is suitable for continuous wave signal and signal search test.
Sample detection method: This detection method is usually applied to noise and "noise-like" signal testing.
NegPeak detection method: suitable for small-signal testing, such as EMC testing.
Normal detection mode: Suitable for simultaneous observation of signal and noise.
Q6: What is the role of tracking source (TG)?
A: The tracking source is one of the common options on the spectrum analyzer. When the tracking source outputs through the input port of the device under test, and the output of the device is connected to the input port of the spectrum analyzer, the spectrum analyzer and the tracking source form a complete adaptive frequency sweep measurement system. The frequency of the signal output from the tracking source can accurately track the tuning frequency of the spectrum analyzer. The spectrum analyzer is equipped with a tracking source option that can be used as a simple scalar network analysis to observe the excitation response characteristics of the device under test, such as the frequency response of the device, insertion loss, and so on.
Q1: How to set the best sensitivity of the spectrum analyzer to facilitate observation of small signal A: firstly set the corresponding center frequency, span (SPAN) and reference level according to the size of the small signal to be measured; then there is no If the signal-to-noise ratio of the small signal to be measured is less than 15dB, the RBW is gradually reduced. The smaller the RBW is, the lower the noise floor of the spectrum analyzer is, and the higher the sensitivity is.
If the spectrum analyzer has a preamp, turn it on. Pre-releasing can increase the noise figure of the spectrum analyzer, thereby increasing the sensitivity. For small signals with low signal-to-noise ratio, VBW can be reduced or trajectory averaging can be used to smooth noise and reduce fluctuations.
It should be noted that the measurement result of the spectrum analyzer is the sum of the external input signal and the internal noise of the spectrum analyzer. To make the measurement result accurate, the signal-to-noise ratio is usually required to be greater than 20 dB.
Q2: The smaller the resolution bandwidth (RBW), the better?
A: The smaller the RBW, the better the spectrum analyzer sensitivity, but the scanning speed will be slower. It is best to set RBW based on actual test requirements to find a balance between sensitivity and speed – both to ensure accurate signal measurement and fast measurement speed.
Q3: How to select the average detection type: Power?Logpower?Voltage?
Logpower Logarithmic Power Average: Also called VideoAveraging, this average mode has the lowest noise floor and is suitable for low-level continuous wave signal testing. However, there is a certain error in the "like-noise" signal, such as the wide-band modulation signal W-CDMA.
Power average: Also known as RMS average, this averaging method is suitable for total power measurement of "noise-like" signals (eg, CDMA).
Voltage averaging: This averaging method is suitable for observing the rise and fall time measurements of amplitude-modulated or pulse-modulated signals.
Q4: Sweep mode selection: Sweep or FFT?
A: The sweep mode of the modern spectrum analyzer usually has Sweep mode and FFT mode. Usually in a narrow RBW setting, FFT is more speed advantage than sweep, but sweep mode is faster under wider RBW conditions.
When the span is smaller than the analysis bandwidth of the FFT, the FFT mode can measure the transient signal; when the span exceeds the FFT analysis bandwidth of the spectrum analyzer, if the FFT scan mode is used, the working method is to segment the signal, segment and segment. If there is discontinuity in time, the useful signal may be lost during the signal sampling gap, and the spectrum analysis will be distorted. This type of signal includes: pulse signals, TDMA signals, FSK modulation signals, and the like.
Q5: The influence of the detector selection on the measurement result?
Peak detection method: Select the maximum value in each bucket as the measurement value. This detection method is suitable for continuous wave signal and signal search test.
Sample detection method: This detection method is usually applied to noise and "noise-like" signal testing.
NegPeak detection method: suitable for small-signal testing, such as EMC testing.
Normal detection mode: Suitable for simultaneous observation of signal and noise.
Q6: What is the role of tracking source (TG)?
A: The tracking source is one of the common options on the spectrum analyzer. When the tracking source outputs through the input port of the device under test, and the output of the device is connected to the input port of the spectrum analyzer, the spectrum analyzer and the tracking source form a complete adaptive frequency sweep measurement system. The frequency of the signal output from the tracking source can accurately track the tuning frequency of the spectrum analyzer. The spectrum analyzer is equipped with a tracking source option that can be used as a simple scalar network analysis to observe the excitation response characteristics of the device under test, such as the frequency response of the device, insertion loss, and so on.
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