Electronics > Projects, Designs, and Technical Stuff
Low frequencies Vector Network Analyzer, arduino based.
<< < (6/20) > >>
MasterT:

--- Quote from: nihtila on September 21, 2018, 07:59:14 pm ---I'm not sure what you mean by "cross-referencing" between bins. Isn't FFT effectively just a bank of narrow bandpass filters?

Try to generate 125kHz digital reference signal (sine) of the same length as your FFT, and use the same windowing. Correlate that with your wideband signal. You will get one number. If I am not completely wrong, that is the same number as your FFT gives for that bin.

--- End quote ---
Effectively yes, it's bank of BPF's. Internally fft engine does cross-correlation  against sine  & cosine And against each others components, there is summ-diff embedded. Exactly this sum-diff feature makes it's so efficient, compare to bank of FIR filters. Running 1024 FIR's (with 1024 kernel length) in parallel  would not be possible on any CPU I know.

Sure you can do cross-correlation with single 125k sine wave, that is another way to get delay or phase shift info. They do same things in all audio and video codec for compression of data, but using optimised version. Simple point-to-point cross-correlation is the highly unefficient operation
MasterT:

--- Quote from: ogden on September 21, 2018, 09:13:53 pm ---
--- Quote from: oPossum on September 21, 2018, 08:58:10 pm ---You really aren't making much sense.

--- End quote ---

If you do not understand what is FFT compared to discrete sine and cosine transform (DFT) then obviously it does not make much sense to you.  |O

--- End quote ---
All this  delusion about DFT /DCT /Wavelets  arises from misunderstanding basic fact, that FFT is the most efficient, accurate and fastest algorithm.
I have another topic on FFT somewhere on this forum, and I already read and know mr. Ogden opinion. Like DCT - do your project with DCT and we will compare results. I don't like this discussion over and over again about difference between DFT DCT wavelet and anything else. There are things that not everyone would ever understand, despite "correct" vocabulary they use.

Regarding terminology Analog Device used in their data sheet on AD5933, right , I didn't read it attentively, and don't care what they call DCT or DFT. What I was expecting from someone who read DS, is a question how I get 0.01 degree phase error compare to 0.5% stated in DS.
ogden:

--- Quote from: MasterT on September 21, 2018, 10:35:16 pm ---All this  delusion about DFT /DCT /Wavelets  arises from misunderstanding basic fact, that FFT is the most efficient, accurate and fastest algorithm.

--- End quote ---

I am not sure who is delusional here. You state that FFT is the most efficient, accurate and fastest algorithm to calculate what exactly? Indeed it is most efficient if you are interested in every bin of it's output, but you are not. You are using just one bin. Look, I am not your mother nor your university. If you still did not get it - so be it. Hopefully other readers of our conversation will do the homework and actually check what I am talking about.


--- Quote ---There are things that not everyone would ever understand, despite "correct" vocabulary they use.

--- End quote ---

Right.  :-DD You use correct vocabulary: FFT?
xaxaxa:
If you multiply your input signal by sine and cosine, then do integrate and dump, the result you get is mathematically equivalent to one frequency bin of your FFT. You can see this just from the formula of the DFT. FFT takes O(n log n) to compute whereas the single frequency DFT takes O(n) even without taking into account memory locality effects, so the integrate and dump is a better choice for this application. Look at my VNA implementation on github (xaxaxa-dev/vna) which does this on an FPGA.
ogden:

--- Quote from: MasterT on September 21, 2018, 02:51:10 pm ---I intended to get comments from the audience that already posses a knowledge  "theory of operation."

--- End quote ---

I am afraid that you are only person who knows "theory of operation" of that circuit which most likely is truly your "design".

[deleted]
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod