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

From: nansai hu
Subject: Re: [Discuss-gnuradio] how to use Log Power FFT module in python
Date: Wed, 16 Dec 2009 20:31:51 -0500

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.
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.

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. :-)


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


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

2009/12/16 Josh Blum <address@hidden>

nansai hu wrote:

I want to do some function in frequency domain and just writen a C++
Now, I just want to use GRC to constuct a front end and connect to my

The interface bewteen these two is a power vector of FFT results and  I
a Log Power FFT module in GRC.

My question is Log Power FFT module in GRC seems that have a very
output format(not stream or vector),

It outputs stream, where each element in the stream is a vector of
with length fft_size.

the output signature of the block is fft_size*sizeof(float)

specifically, what problem are you having?


 So what is the format of that module and How clould I use it if my C++

have a float vector input(512 points power result of FFT).



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