Re: [Discuss-gnuradio] How to write vector to a file

[Marcus D. Leech]

> Thanks Josh,
>
> You got it right, self.u is USRP2. I am converting the stream which 
> comes from self.u into vector by using the s2v (stream to vector) 
> function. And now I want to capture the IQ data.
>
> gr.file_sink() writes only streams into a file I guess, so  I was 
> looking for any other gnuradio class which can write vectors too into 
> a file. Do you think that gr.file_sink() can do the same thing?
>
> Also, When I use gr.file_sink(), the sensing does not automatically 
> and I have to stop it manually(ctrl+z) after a while. I am wondering 
> if there is any other way so that the usrp2 can sense a certain 
> frequency band for a certain period and can switch to another 
> frequency then.
> And one more thing, using gr,file_sink() and storing the raw complex 
> data, I found that many data are giving 0 value. I think regardless of 
> the frequency band, the raw data should contain some value, it might 
> be very small but not zero. Do you any reason for that?
>
> Thank you;
Not sure why you want the vector format.  A vector in Gnu Radio is just 
a fixed-sized "slab" of samples, and since you're just recording them
  to disk, there's no reason to treat them in a vector format inside 
the flow-graph.  Certain transforms, like the FFT, require their inputs to
  be fixed-sized "vectors", but a simple stream-record-to-disk has no 
such requirement.

You haven't discussed your hardware setup in detail.  What 
daughtercards?  What frequency are you tuning to? Have you set the RF 
gain controls appropriately?

The I/Q data are voltage-samples of a quasi-sinusoidal phenomenon--why 
would you *not* expect such a phenomenon to regularly and
  frequently pass-through the zero point?

If you're programming in raw Python, can I suggest you look into Gnu 
Radio companion?  It makes things easier in many ways.

Also, if you want to "sample for a little while then stop", you can 
create a separate thread that simply goes to sleep for awhile, and when it
  wakes up, it calls tb.stop(), where "tb" is whatever you've named 
your top flow-graph block.

--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org