Help plotting FFT from column vector with real and imaginary parts.

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Robert Evans
Robert Evans 2015-11-30
评论： Joseph Nichols 2023-6-24
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.

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采纳的回答

Rick Rosson
Rick Rosson 2015-12-1
编辑：Rick Rosson 2015-12-1
N = length(data);
freq = fftshift(fft(data))/N;
plot(abs(freq));

更多回答（1 个）

Robert Evans
Robert Evans 2015-12-1
Thank you very much.

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