Re: [Discuss-gnuradio] how to use Log Power FFT module in python

[Josh Blum]

nansai hu wrote:
> Many Thanks.
> I use a file sink to received the result of Log Power FFT and it can be
> excute successfully.
> But the file which I saved is hard to read and understand.

Its binary floating point data.

> In my mind, I think a scenario like this:
> I use a signal generater to transmit a signal, then I use USRP to received.
> USRP include a USRP source,a Log Power FFT and a File sink.
> When I transmit a CW signal,I imagine that I could get the file data in
> 512points(one snapshot) and see a peak value and noise in other 511 points.

Im not sure that the problem is. There is a graphical fft sink in grc, 
so you can look at a live/running fft plot.

> 2009/12/16 Josh Blum <address@hidden>
>
> > A few ways I can think of off-hand:
> >
> > 1) make a custom gr.hier_block2 in python, it can read from a message queue
> >
> > 2) use a file sink to dump the data from the log power fft to file,
> > post-process the file
> >
> > 3) you could use the variable sink in grc to write the fft vectors to a
> > variable called fft_vec. Then another variable could be print(str(fft_vec)).
> > I think it would actually work, but I have not tried. :-)
> >
> > -josh
> >
> >
> > nansai hu wrote:
> >
> > > Ok. I add a vector sink in GRC and to observe the data in that module.
> > > But when I run GRC there is no result shown. I need to add some other
> > > block
> > > to see or I need write some code like "prinf" in Python?
> > >
> > >
> > >
> > > 2009/12/16 Josh Blum <address@hidden>
> > >
> > > all blocks that have:
> > > > 1) a float input/sink port
> > > > 2) a vector length set to fft_size
> > > >
> > > > -josh
> > > >
> > > >
> > > > nansai hu wrote:
> > > >
> > > > My question is I can't find any module in GRC can be conncet to Log Power
> > > > > FFT module in right format.
> > > > > Could you tell me which module in GRC can be use to receive Log Power
> > > > > FFT
> > > > > module?
> > > > >
> > > > > 2009/12/16 Josh Blum <address@hidden>
> > > > >
> > > > >
> > > > > nansai hu wrote:
> > > > > > I want to do some function in frequency domain and just writen a C++
> > > > > >
> > > > > > > block
> > > > > > > already.
> > > > > > > Now, I just want to use GRC to constuct a front end and connect to my
> > > > > > > own
> > > > > > > block.
> > > > > > >
> > > > > > > The interface bewteen these two is a power vector of FFT results and
> > > > > > >  I
> > > > > > > use
> > > > > > > a Log Power FFT module in GRC.
> > > > > > >
> > > > > > > My question is Log Power FFT module in GRC seems that have a very
> > > > > > > strange
> > > > > > > output format(not stream or vector),
> > > > > > >
> > > > > > > It outputs stream, where each element in the stream is a vector of
> > > > > > floats
> > > > > > with length fft_size.
> > > > > >
> > > > > > the output signature of the block is fft_size*sizeof(float)
> > > > > >
> > > > > > specifically, what problem are you having?
> > > > > >
> > > > > > -josh
> > > > > >
> > > > > >  So what is the format of that module and How clould I use it if my C++
> > > > > >
> > > > > > block
> > > > > > > have a float vector input(512 points power result of FFT).
> > > > > > >
> > > > > > > Thanks
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >
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> > > > > > >
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