
From:  S. L. 
Subject:  Re: [Discussgnuradio] Question about stream to complex and fft 
Date:  Fri, 14 Jun 2019 12:26:45 +0000 
Thank you very much for your responses
So, if for example, I want to simulate 1 second of a cosine wave of 1K, with sample rate of 32K as the example and I have a very powerful computer the signal source block (cosine) could generate the 32k samples in 0.5 seconds , but the 32K wave samples
of a 1K would correspond to real (good) values as if it had been sampling for 1 second ... Is that correct?
And if I put a Throttle block at the output of the signal source block at 32K of sample rate, the throttle block will receive the 32k samples as input at a lower time, store them in a buffer and direct them to the output at the precise moment, it is say
every 1 / 32K ms ... Is this correct?
De: Kyeong Su Shin <address@hidden>
Enviado: viernes, 14 de junio de 2019 13:31 Para: S. L.; address@hidden Asunto: RE: Question about stream to complex and fft Hello S.L:
That sounds correct to me.
One note, however: the sampling rate in GNU Radio is just a conceptual thing, and does not determine the 'actual time that GNU Radio takes to generate or consume the samples', if you do not use hardware sinks/sources (like SDR sources) and/or throttle blocks. If your flowgraph does not have such blocks, then the flowgraph will execute 'as fast as it can'. The data generated by your program will be still correct; it is just that the 'time' is just a conceptual thing (so as you don't have to deal with normalized sampling rates) and may not agree with the actual execution speed of the program.
Kyeong Su Shin
보낸 사람: S. L. <address@hidden> 대신 Discussgnuradio <discussgnuradiobounces+ksshin=address@hidden>
보낸 날짜: 2019년 6월 14일 금요일 오후 6:08:55 받는 사람: address@hidden 제목: [Discussgnuradio] Question about stream to complex and fft
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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