Re: [Discuss-gnuradio] File sink: file size

[Ellie White]

Oops, forgot to reply all!

From: Ellie White
Sent: Thursday, April 20, 2017 9:57 PM
To: Marcus D. Leech <address@hidden>
Subject: RE: [Discuss-gnuradio] File sink: file size

Hi Marcus -

Apologies for the delayed response! Thanks for your helpful input and for 
sending the link to your SID repository.  It looks like it is full of useful 
stuff; however when I tried to run the .grc file, it shows that a lot of blocks 
are missing - is there some way I can fix that? Do I need to install some 
blocks from a different location, or did I just do something wrong when I 
cloned the repository and ran the Makefile? (I'm super new to GitHub, so it 
could certainly be some incompetence on my part related to that).

Also, based on your experience, what do you think is a good channel bandwidth?

Thanks again!

Ellie

From: Discuss-gnuradio [mailto:address@hidden On Behalf Of Marcus D. Leech
Sent: Friday, April 7, 2017 10:16 PM
To: address@hidden<mailto:address@hidden>
Subject: Re: [Discuss-gnuradio] File sink: file size

On 04/07/2017 02:53 PM, Ellie White wrote:
Hello,

As I've mentioned in an earlier email to this list, I'm working on a small loop 
antenna with the purpose of monitoring solar activity. I am currently reading 
in the data through an RTL-SDR source, flowgraph attached.

For this project, I need to be able to let my antenna run for long periods of 
time (upwards of an hour or more, preferably several hours) in order to get a 
graph of signal intensity vs. time. Right now, my setup consists of the GNU 
Radio flowgraph attached, that produces a file which I analyze using a Python 
program to get a spectral plot and a time series (for one of the 1024 channels 
saved in the file).

I let my antenna and GNU Radio run for about 15 minutes last night collecting 
data, and the file size ended up at over 7 GB. I am wondering if there is any 
way to reduce the size of the file without tremendously reducing the quality of 
the data? I have a few ideas on this, but I'm hoping someone else will have 
better ones:

-Maybe I need to reduce the sample rate.

-Another option is to somehow just save the channel I need to the file, instead 
of all 1024. Does anyone have any advice as to how to accomplish that?

If you need any more information or if I should clarify anything, please let me 
know. Thanks!

Ellie



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You might also take a look at my work from 6 or 7 years ago:

https://github.com/patchvonbraun/SIDSuite

It uses audio input.  It uses a set of Gortzel transforms to pick out the 
channels of interest.

But there are other approaches, using an FFT as you have.

Since the things that you're looking for unfold over timescales of many-seconds 
to many-minutes, you don't need to be logging your FFT output in
  real-time.  You could easily integrate for several seconds and dump output 
data at a lower rate, using keep-one-in-N.

At an input rate of 2Msps, your 1024-point FFT will be producing 1953 1024-bin 
vectors/second.  This is *much* faster than the timescale of ionospheric
  events, in my experience.  Also, your frequency resolution will be somewhat 
coarse-1953Hz.  This is much wider bandwidth than the naval stations
  you're looking at, so you'll mostly be integrating noise, rather than navy 
signal, in your bins.

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