Ceyear 4051 Series, Руководство пользователя

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4. Operating Instruction
4.1 Function operation guide
65
Prompt
Judge the parasitic or residual response of Series Signal Analyzer by changing sweep time
The 4051 Series Signal/Spectrum Analyzer can carry out the spectrum measurement by using sweep and FFT.
When you find the lesser parasitic or residual response on the measured data, you can try to judge that the
response is generated by Series Signal Analyzer itself or brought into by the input signal by changing the
sweep type. If the response signal disappears or gets smaller in different sweep type, it can be considered that
the signal distortion to a certain degree is caused by the hardware measurement channel of Series Signal
Analyzer.
 Configure FFT width manually
The FFT width can be set by activating the [Sweep Type ▶ ] and [FFT Width ▶ ] though 【 Sweep 】 key on the
front panel.
Before the FFT width is set manually, the working principle and process that 4051 Series Signal/Spectrum
Analyzer executes the FFT spectrum measurement should be understood first. When the FFT is used to
measure the signal spectrum within one frequency range, the Series Signal Analyzer is tuned to center
frequency of measured frequency range, then the FFT spectrum calculation is carried out for the time domain
data obtained. As the limitation of resolution bandwidth, the maximum frequency range of this way of
measurement is also limited with limit value of FFT width. For the spectrum measurement of frequency range
exceeding the FFT width, the Series Signal Analyzer will measure one section of frequency range at a time by
tuning the center frequency of RF reception circuit by step and joint the measured spectrum.
FFT width is only active when the FFT sweep type is selected. When the sweep type is set as auto, the 4051
Series Signal/Spectrum Analyzer will execute FFT spectrum measurement, the maximum resolution
bandwidth is 1 MHz. The larger is the FFT width, the faster is FFT spectrum measurement, but the dynamic
range performance will be affected.
Under FFT sweep, the FFT width setup limits the maximum value for center frequency step of each tune. For
example, if [<100Hz] is selected, the maximum value for center freq step of each tune is 100Hz. As the FFT
width gets larger, the count of instrument center frequencies get smaller when performing measurement of
same frequency scope, and the response measurement gets faster. Therefore, to improve measurement speed,
you can manually change the FFT width.
Caution
The maximum FFT
If the FFT width is set as [<= Maximum Value], the maximum FFT is 10 MHz under standard configuration.
7) Select the filter bandwidth and type reasonably
 Configure filter type manually
The filter type can be selected manually by activating the [Filter Type] through
【
BW
】
key on the front
panel.
In general, the 4051 Series Signal/Spectrum Analyzer uses Gaussian filter, i.e., use filter approximate to the
Gaussian shape to complete filtering of resolution bandwidth. If the flat top filter is used, the Series Signal
Analyzer adopts filter approximate to the rectangular shape to complete filtering of resolution bandwidth. The
response time of flat top filter of 4051 Series Signal/Spectrum Analyzer is about 3 times of that of the
Gaussian filter, as the sweep speed of the flat top filter is smaller than that of the Gaussian filter. The flat top