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

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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.

Accepted Answer

Rick Rosson
Rick Rosson on 1 Dec 2015
Edited: Rick Rosson on 1 Dec 2015
N = length(data);
freq = fftshift(fft(data))/N;
plot(abs(freq));

More Answers (1)

Robert Evans
Robert Evans on 1 Dec 2015
Thank you very much.

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