Plotting spectrograph from spectrum analyzer data

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Hans H
Hans H 2024 年 2 月 23 日
コメント済み: Star Strider 2024 年 2 月 28 日
I have the following data obtained the following data from a spectrum analyzer. I need some pointers on plotting it to obtain the spectrogram as shown in this image
I have attached my data in this question. The Header contains data from the instrument (such as center frequency) and the Timedata has unsigned array of 10x131071 and Value has the value at each point of time (same size)
_________________
I tried using the following but to no avail
% Convert time_data to double and calculate the sampling frequency
dt = double(time_data(1, 2) - time_data(1, 1)); % Assuming a constant time interval
fs = 1 / dt;
% Transpose the amplitude_data matrix
amplitude_data = amplitude_data';
% Number of rows in amplitude_data
num_rows = size(amplitude_data, 1);
% Plot spectrogram for each row
for row = 1:num_rows
figure;
spectrogram(amplitude_data(row, :), hamming(256), 250, 256, fs, 'yaxis');
title(['Spectrogram for Row ', num2str(row)]);
xlabel('Time');
ylabel('Frequency');
colorbar; % Display the color scale
end
  1 件のコメント
Mario Malic
Mario Malic 2024 年 2 月 23 日
Can you also include the code that loads the files please?

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Star Strider
Star Strider 2024 年 2 月 23 日
Yiour data needed a bit of tweaking. Tehe times in the ‘TimeData’ matrix are contiguous, so they can be converted into a vector using reshape, and then the same with the ‘Values’ matrix.
Try this —
files = dir('*.mat');
for k = 1:numel(files)
load(files(k).name)
end
% Header
TimeData = double(TimeData);
TimeV = sort(reshape(TimeData.', [], 1)); % Vector From Matrix
Ts = mean(diff(TimeV))
Ts = 2.2249e+04
fs = 1/Ts
fs = 4.4946e-05
ValuesV = reshape(Values.', [], 1); % Vector From Matrix
figure
semilogy(TimeV, ValuesV)
xlabel('Time (unit)')
ylabel('Amplitude nit)')
figure;
spectrogram(ValuesV, hamming(256), 250, 256, fs, 'yaxis');
% title(['Spectrogram for Row ', num2str(row)]);
xlabel('Time');
ylabel('Frequency');
colormap(turbo)
colorbar; % Display the color scale
[p,f,t] = pspectrum(ValuesV,fs,'spectrogram');
figure
surfc(f,t,p', 'EdgeColor','interp')
xlabel('Frequency (cycles/time unit)')
ylabel('Time (unit)')
zlabel('Magnitude')
wtf = gca;
wtf.XDir = 'reverse';
view([30 45])
colormap(turbo)
colorbar
figure
surfc(f,t,mag2db(p'), 'EdgeColor','interp')
xlabel('Frequency (cycles/time unit)')
ylabel('Time (unit)')
zlabel('Magnitude (dB)')
wtf = gca;
wtf.XDir = 'reverse';
view([30 45])
colormap(turbo)
colorbar
figure
surfc(f,t,mag2db(p'), 'EdgeColor','interp')
xlabel('Frequency (cycles/time unit)')
ylabel('Time (unit)')
zlabel('Magnitude (dB)')
wtf = gca;
wtf.XDir = 'reverse';
view([30 45])
colormap(turbo)
hcb = colorbar;
hcb.Label.String = 'Magnitude (dB)';
view(90,90)
I did this with both spectrogram and pspectrum (that I actually prefer fot these sorts of analyses).
.
  4 件のコメント
Hans H
Hans H 2024 年 2 月 28 日
Thanks again, Star Strider. You always outdo yourself!
(I think the only way to get the frequency is to do it manually--create an array with the same size as the values, starting at center freq-span/2, and ending at center freq+span/2.
Thanks again!
Star Strider
Star Strider 2024 年 2 月 28 日
As always, my pleasure!
It would help to know what the actual time values are. They must correspond to something useful, however I cannot figure out how to convert them.

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