Help plotting FFT from column vector with real and imaginary parts.
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Robert Evans
am 30 Nov. 2015
Kommentiert: Joseph Nichols
am 24 Jun. 2023
Hello, I'm attempting to plot the fft from the data taken from an oscilloscope and saved in Excel.
I've saved the data in matlab as a column vector with 200 data points of real and imaginary parts, called 'data', and I'm trying to get an accurate FFT plot. The plot that comes out doesn't look like the FFT spikes I'm expecting; rather its just a strange squiggle. I was wondering if anybody has any insight into what I'm doing wrong. My code is:
>> freq = fft (data)
freq =
-1.2128 + 0.0000i
2.1644 + 5.0673i
0.2578 + 1.0098i
0.0654 + 0.6253i
0.0270 + 0.4352i
0.0174 + 0.3877i
0.0068 + 0.3035i
-0.0008 + 0.2554i
-0.0048 + 0.2123i
-0.0101 + 0.1999i
0.0021 + 0.1944i
-0.0191 + 0.1507i
-0.0352 + 0.1421i
-0.0275 + 0.1331i
-0.0235 + 0.1287i
-0.0528 + 0.1290i
-0.0094 + 0.0996i
-0.0388 + 0.0833i
-0.0216 + 0.0892i
-0.0338 + 0.0902i
-0.0159 + 0.0837i
-0.0284 + 0.0609i
-0.0360 + 0.0834i
-0.0358 + 0.0962i
-0.0206 + 0.0791i
-0.0261 + 0.0670i
-0.0314 + 0.0603i
-0.0204 + 0.0536i
-0.0122 + 0.0511i
-0.0247 + 0.0404i
-0.0297 + 0.0425i
-0.0275 + 0.0417i
-0.0325 + 0.0510i
-0.0250 + 0.0568i
-0.0192 + 0.0415i
-0.0296 + 0.0531i
-0.0199 + 0.0475i
-0.0255 + 0.0470i
-0.0340 + 0.0470i
-0.0225 + 0.0298i
-0.0254 + 0.0361i
-0.0179 + 0.0413i
-0.0312 + 0.0294i
-0.0364 + 0.0124i
-0.0237 + 0.0331i
-0.0264 + 0.0207i
-0.0172 + 0.0344i
-0.0181 + 0.0243i
-0.0486 + 0.0343i
-0.0056 + 0.0411i
-0.0436 + 0.0328i
-0.0230 + 0.0237i
-0.0372 + 0.0243i
-0.0291 + 0.0368i
-0.0212 + 0.0038i
-0.0266 + 0.0212i
-0.0309 + 0.0148i
-0.0411 + 0.0130i
-0.0279 + 0.0245i
-0.0151 + 0.0134i
-0.0347 + 0.0158i
-0.0324 + 0.0211i
-0.0287 + 0.0202i
-0.0305 + 0.0307i
-0.0145 + 0.0180i
-0.0227 + 0.0106i
-0.0480 + 0.0169i
-0.0270 + 0.0098i
-0.0301 + 0.0193i
-0.0271 + 0.0160i
-0.0410 + 0.0047i
-0.0239 + 0.0182i
-0.0198 + 0.0074i
-0.0419 + 0.0206i
-0.0228 + 0.0139i
-0.0150 + 0.0014i
-0.0281 + 0.0141i
-0.0280 + 0.0145i
-0.0460 + 0.0218i
-0.0194 + 0.0152i
-0.0303 - 0.0020i
-0.0215 + 0.0226i
-0.0372 - 0.0002i
-0.0243 + 0.0146i
-0.0262 + 0.0152i
-0.0350 + 0.0149i
-0.0252 + 0.0092i
-0.0154 + 0.0027i
-0.0391 - 0.0037i
-0.0301 + 0.0099i
-0.0439 - 0.0088i
-0.0103 + 0.0423i
-0.0094 - 0.0096i
-0.0434 + 0.0049i
-0.0310 + 0.0006i
-0.0493 + 0.0002i
0.0009 + 0.0156i
-0.0324 - 0.0052i
-0.0360 + 0.0146i
-0.0138 - 0.0139i
-0.0548 + 0.0000i
-0.0138 + 0.0139i
-0.0360 - 0.0146i
-0.0324 + 0.0052i
0.0009 - 0.0156i
-0.0493 - 0.0002i
-0.0310 - 0.0006i
-0.0434 - 0.0049i
-0.0094 + 0.0096i
-0.0103 - 0.0423i
-0.0439 + 0.0088i
-0.0301 - 0.0099i
-0.0391 + 0.0037i
-0.0154 - 0.0027i
-0.0252 - 0.0092i
-0.0350 - 0.0149i
-0.0262 - 0.0152i
-0.0243 - 0.0146i
-0.0372 + 0.0002i
-0.0215 - 0.0226i
-0.0303 + 0.0020i
-0.0194 - 0.0152i
-0.0460 - 0.0218i
-0.0280 - 0.0145i
-0.0281 - 0.0141i
-0.0150 - 0.0014i
-0.0228 - 0.0139i
-0.0419 - 0.0206i
-0.0198 - 0.0074i
-0.0239 - 0.0182i
-0.0410 - 0.0047i
-0.0271 - 0.0160i
-0.0301 - 0.0193i
-0.0270 - 0.0098i
-0.0480 - 0.0169i
-0.0227 - 0.0106i
-0.0145 - 0.0180i
-0.0305 - 0.0307i
-0.0287 - 0.0202i
-0.0324 - 0.0211i
-0.0347 - 0.0158i
-0.0151 - 0.0134i
-0.0279 - 0.0245i
-0.0411 - 0.0130i
-0.0309 - 0.0148i
-0.0266 - 0.0212i
-0.0212 - 0.0038i
-0.0291 - 0.0368i
-0.0372 - 0.0243i
-0.0230 - 0.0237i
-0.0436 - 0.0328i
-0.0056 - 0.0411i
-0.0486 - 0.0343i
-0.0181 - 0.0243i
-0.0172 - 0.0344i
-0.0264 - 0.0207i
-0.0237 - 0.0331i
-0.0364 - 0.0124i
-0.0312 - 0.0294i
-0.0179 - 0.0413i
-0.0254 - 0.0361i
-0.0225 - 0.0298i
-0.0340 - 0.0470i
-0.0255 - 0.0470i
-0.0199 - 0.0475i
-0.0296 - 0.0531i
-0.0192 - 0.0415i
-0.0250 - 0.0568i
-0.0325 - 0.0510i
-0.0275 - 0.0417i
-0.0297 - 0.0425i
-0.0247 - 0.0404i
-0.0122 - 0.0511i
-0.0204 - 0.0536i
-0.0314 - 0.0603i
-0.0261 - 0.0670i
-0.0206 - 0.0791i
-0.0358 - 0.0962i
-0.0360 - 0.0834i
-0.0284 - 0.0609i
-0.0159 - 0.0837i
-0.0338 - 0.0902i
-0.0216 - 0.0892i
-0.0388 - 0.0833i
-0.0094 - 0.0996i
-0.0528 - 0.1290i
-0.0235 - 0.1287i
-0.0275 - 0.1331i
-0.0352 - 0.1421i
-0.0191 - 0.1507i
0.0021 - 0.1944i
-0.0101 - 0.1999i
-0.0048 - 0.2123i
-0.0008 - 0.2554i
0.0068 - 0.3035i
0.0174 - 0.3877i
0.0270 - 0.4352i
0.0654 - 0.6253i
0.2578 - 1.0098i
2.1644 - 5.0673i
>> plot (freq)
Any help would be appreciated.
0 Kommentare
Akzeptierte Antwort
Rick Rosson
am 1 Dez. 2015
Bearbeitet: Rick Rosson
am 1 Dez. 2015
N = length(data);
freq = fftshift(fft(data))/N;
plot(abs(freq));
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