| Electronics > Projects, Designs, and Technical Stuff |
| Low frequencies Vector Network Analyzer, arduino based. |
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| MasterT:
--- Quote from: xaxaxa on September 22, 2018, 01:47:56 am ---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. --- End quote --- I was able to locate your project on github, and download a tar-ball. Can't find dsp processing, where do you calculate phase/magnitude? Is this in fpga? Could I run your dsp core in Qt for evaluation purposes? I couldn't see any metrological parameters for phase error, have any data? |
| MasterT:
--- Quote from: ogden on September 22, 2018, 03:11:44 pm ---Show post. --- End quote --- Can't read you, blacklisted by very nice "Ignore" feature on this forum. |
| ogden:
--- Quote from: MasterT on September 22, 2018, 03:47:00 pm --- --- Quote from: ogden on September 22, 2018, 03:11:44 pm ---Show post. --- End quote --- Can't read you, blacklisted by very nice "Ignore" feature on this forum. --- End quote --- Ok. You do not deserve my input anymore anyway. Warning to others: his circuit has many flaws, better do not copy it. |
| Kleinstein:
For just using 1 or 2 bins (as one also needs the phase) from the FFT it is usually faster to just calculate those 2 bins by DFT. The FFT is very efficient if many bins are needed, like in a spectrum analyzer function, but not for a simple lock in / VNA type measurement. The advantage of DFT is that is can be done in real time, without even saving all the samples. Its just a few running sums and than from time to time the final result. |
| MasterT:
--- Quote from: Kleinstein on September 22, 2018, 04:53:16 pm ---For just using 1 or 2 bins (as one also needs the phase) from the FFT it is usually faster to just calculate those 2 bins by DFT. The FFT is very efficient if many bins are needed, like in a spectrum analyzer function, but not for a simple lock in / VNA type measurement. --- End quote --- Probably, you didn't read what I already explain using hardware analogy with MUX-ers, that running FFT would reduce noise floor in single bin bucket? In other words, provides >30 dB (fft-2048) improvements in SNR ratio ? |
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