
From:  S. L. 
Subject:  [Discussgnuradio] Question about stream to complex and fft 
Date:  Fri, 14 Jun 2019 09:08:55 +0000 
Hello, I have a question about the realtime operation of gnuradio and the "streamtovector" and FFT modules "
In the example image I have:
variable samp_rate to 32K
and the following flowchart:
Signal source (waveform: cosine, sample_rate: 32K, frecuency: 1K) > streamtovector (Num items: 1024) > FFT (size: 1024) > ComplextoMag (Vector lenght: 1024)  > QT GUI Vector Sink (Vector size: 1024)
Then cosine has 1K of frequency and sample rate is 32K and FFT size is 1024
I'm not really sure how the gnuradio simulation works so I'd like to check it with you and see if I'm right or I'm wrong
A whole cosine wave would take 1ms
since the sample rate is 32K, a cosine wave would be 32 samples
Then 1024 samples would be 1024/32 = 32 cosine waves, that is 32 * 1 ms = 32 ms
Then:
Since I have vectortostream and fft to 1024 samples, I think or I guess it stores the first 1024 samples (from 0 ms to 32 ms) and the vectortostream module passes those samples to the FFT module that performs the FFT of those 1024 samples
Then another 1024 samples (form 32 ms to 64 ms) would arrive and I would pass those samples to the FFT
That is, the FFT block performs its function every 32 ms with 1024 sample vectors
Is this operating logic on the streamtovector and fft block correct? or I'm wrong
Thank you very much everyone for your time
a greeting 
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