FFT窗口问题和差异

作业时间！
使用深记忆示波器进行光谱分析快速傅立叶变换（FFT）AN 1383-1 http://literature.cdn.keysight.com/litweb/pdf/5988-4368EN.pdf大多数测量需要使用窗口，如
汉宁或平顶窗户。
这些是用于典型频率分析测量的适当窗口。
在这两个窗口之间进行选择涉及频率分辨率和幅度精度之间的折衷。
汉宁•优势：良好的频率分辨率•缺点：振幅精度降低汉明•优势：良好的频率分辨率（略好于汉宁）•缺点：振幅精度较低平顶•优势：良好的振幅精度•缺点：频率分辨率较低矩形•优点：良好
频率分辨率，良好的幅度精度（适用于自窗口波形）•缺点：可能的泄漏影响Blackman-Harris•优点：适用于具有强干扰分量且距离您想要看到的频率相当远的信号，良好的通用窗口免责声明
：要获得更可靠的响应，您应该考虑致电当地的安捷伦技术呼叫中心。
安捷伦论坛在“可用”的基础上进行监控，并不一定是解决技术问题的最快方式。



     以下为原文

  Homework time!

Spectral Analysis Using a Deep-Memory Oscilloscope Fast Fourier Transform (FFT) AN 1383-1
http://literature.cdn.keysight.com/litweb/pdf/5988-4368EN.pdf 
 
Most measurements will require the use of a window such as the Hanning or Flattop windows. These are the appropriate windows for typical frequency analysis measurements. Choosing between these two windows involves a trade-off between frequency resolution and amplitude accuracy.
Hanning
•     Advantage: Good Frequency Resolution
•     Disadvantage: Less Amplitude Accuracy
Hamming
•     Advantage: Good Frequency Resolution (slightly better than Hanning)
•     Disadvantage: Less Amplitude Accuracy
Flattop
•     Advantage: Good Amplitude Accuracy
•     Disadvantage: Less Frequency Resolution
Rectangular
•     Advantage: Good Frequency Resolution, Good Amplitude Accuracy (For self-windowing waveforms)
•     Disadvantage: Possible Leakage Effects
Blackman-Harris
•     Advantage: Good for signals with a strong interference component that is fairly distance from the frequency you want to see, good general purpose window


Disclaimer: For more reliable response, you should consider calling your local Agilent Technical Call Center. The Agilent Forums are monitored on an "as available" basis, and aren't necessarily the fastest way to get technical questions answered.

请记住，每个窗口都具有调制波形的效果，并将能量从峰值扩散到边带。
B-H窗口做得最多，当峰值向下移动时，边带向上移动。
它对分辨率BW也有很大影响。
人



     以下为原文

  Remember that every window has the effect of modulating the waveform, and spreading the energy from the peaks into the sidebands. The B-H window does that the most, and while the peak moves down, the sidebands move up. It also has a large effect on the Resolution BW.

Al

感谢您的回复。我同意每个窗口都有自己的优势和优势。
缺点。
Blackman Harris会降低振幅，但我担心的是它将峰值降低了10dBm，这可能会使测量测试失败，达到规格限制。
所以我担心通过布莱克曼哈里斯窗口的结果是否可以接受或是否与范围有关？是否有人尝试在安捷伦示波器中使用此窗口？
我想了解在这种情况下使用B-H窗口进行FFT测量时幅度精度是否良好。
VJEdited：VJ于2014年9月15日晚上11:44



     以下为原文

  Thank you for the response.I agree that each window has its own advantage & disadvantages.
And the Blackman Harris would reduce the amplitude but my concern is that it has reduced the peak by 10dBm which could make a measurement test fail with respect to a spec limit.

So i m concerned  whether the result i get through Blackman Harris window is acceptable or is it some issue with scope?Anybody have tried using this window in Agilent scope?

I want to understand if the amplitude accuracy is good when using B-H window for FFT measurements in this condition.

VJ

Edited by: VJ on Sep 15, 2014 11:44 PM

“在这种情况下使用B-H窗口进行FFT测量时，我想了解幅度精度是否良好。”
然后你需要学习一些FFT理论并用其他工具进行一些实验，比如MATLAB或任何免费的替代品，甚至是Excel。
将捕获的跟踪文件保存到csv，将其导入您喜欢的程序，然后使用各种窗口选项。
峰的扩展意味着一些显示的能量移动到其他桶，从而减少了较高峰中显示的能量并增加了较低峰的能量。
这就像在'真实'FFT上运行平滑功能（顺便说一下，它不存在）。
所有窗口中包含的总能量对于所有窗口函数应该是相同的（除了实际窗口本身引起的损失）。
在我看来，如果您担心振幅精度，B-H窗口不适合使用。
人



     以下为原文

  "I want to understand if the amplitude accuracy is good when using B-H window for FFT measurements in this condition."

Then you need to learn some FFT theory and run some experiments with other tools, such as MATLAB or any of the free alternatives, or even Excel. Save the captured trace file to a csv, import it into your favorite program, and play with the various windowing options.

Spreading of the peaks means that some of the displayed energy moves to other buckets, thus reducing the energy shown in the higher peaks and increasing the energy on the lower peaks. It's like running a smoothing function over the 'real' FFT (which doesn't exist, by the way). The total energy included in all of the buckets should be the same for all windowing functions (except for the loss caused by the actual window itself).

It appears to me that the B-H window is not the right one to use if you are worried about amplitude accuracy.

Al