Teach you how to choose a low frequency/spectrum analyzer

The spectrum analyzer is a multi-purpose electronic measuring instrument. It mainly measures signal parameters such as signal distortion, modulation degree, spectral purity, frequency stability and intermodulation distortion. If the spectrum analyzer is used for a long time, malfunctions may occur due to various factors. Then follow Antai Test to choose a spectrum analyzer.

1. How to set up the sensitivity of the spectrum analyzer to facilitate the observation of small signals?

First, set the corresponding center frequency, span (SPAN) and reference level according to the size of the small signal being measured; then gradually reduce the attenuation value if there is no overload prompt on the spectrum analyzer; if the signal of the small signal being measured is When the noise ratio is less than 15dB, gradually reduce the RBW. The smaller the RBW, the lower the noise floor of the spectrum analyzer and the higher the sensitivity.

If the spectrum analyzer has a preamp, turn it on. Pre-release can improve the noise figure of the spectrum analyzer, thus improving the sensitivity. For small signals with low signal-to-noise ratio, VBW can be reduced or trajectory average can be used to smooth the 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 results accurate, the signal-to-noise ratio is usually required to be greater than 20dB.

2. Is the smaller the resolution bandwidth (RBW), the better?

The smaller the RBW, the better the spectrum analyzer sensitivity, but the sweep speed will be slower. Set according to actual test requirements

RBW, finds a balance between sensitivity and speed – ensuring accurate signal measurement and fast measurement speed.

3. How to choose the average detection method (averagetype): power? Logpower? Voltage?

·Logpower logarithmic power average

Also known as VideoAveraging, this averaging method has a low noise floor and is suitable for low-level continuous wave signal testing. However, there will be certain errors for "noise-like" signals, such as wideband modulated signals such as W-CDMA.

·Power average

Also called RMS averaging, this averaging method is suitable for total power measurement of "noise-like" signals (such as CDMA).

·Voltage average

This averaging method is suitable for observing rise and fall time measurements of amplitude modulated signals or pulse modulated signals.

4.Selection of scanning mode: sweep or FFT?

The sweep mode of modern spectrum analyzers usually has Sweep mode and FFT mode. Generally, FFT has a speed advantage over sweep at narrow RBW settings, but sweep mode is faster at wider RBW conditions.

When the span is smaller than the FFT analysis bandwidth, the FFT mode can measure transient signals; when the span exceeds the FFT analysis bandwidth of the spectrum analyzer, if the FFT scanning mode is used, the working method is to segment the signal, segment by segment. If there is a discontinuity in time between them, the useful signal may be lost during the signal sampling gap, and the spectrum analysis will be distorted. This type of signal includes: pulse signal, TDMA signal, FSK modulated signal, etc.

5. How does the choice of detector affect the measurement results?

·Peak detection method

Select the value in each bucket as the measurement value. This detection method is suitable for continuous wave signals and signal search testing.

·Sample detection method

This detection method is usually suitable for testing noise and "noise-like" signals.

·NegPeak detection method

Suitable for small signal testing, such as EMC testing.

·Normal detection mode

Suitable for observing signal and noise simultaneously.

6. What is the role of tracking source (TG)?

Tracking sources are one of the common options on spectrum analyzers.

When the output of the tracking source passes 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 by the tracking source can accurately track the tuning frequency of the spectrum analyzer.

With the tracking source option, the spectrum analyzer can be used for simple scalar network analysis to observe the excitation response characteristic curve of the device under test, such as the frequency response and insertion loss of the device.