Re: [Discuss-gnuradio] Handling of IQ files

[Henry Barton]

I’ve read up on the FFT and DSP and I must say I’m impressed that multiplying two waveforms is the digital equivalent of heterodyning. Am I right in my understanding that finding frequency components (FFT-ing) is simply multiplying a series of known sine waves by your input waveform?

Sent from Windows Mail

From: Nate Temple
Sent: ‎Saturday‎, ‎March‎ ‎19‎, ‎2016 ‎2‎:‎51‎ ‎PM
To: Henry Barton
Cc: address@hidden

Hi Henry,

Here are a few open source applications you may find useful to reference to build your tool.

rtl_power + heatmap.py (c/python) - Hard coded to use the RTL-SDRs
https://github.com/keenerd/rtl-sdr/blob/master/src/rtl_power.c
http://kmkeen.com/rtl-power/

rtl_power port that uses FFTW - https://github.com/AD-Vega/rtl-power-fftw

inspectrum (c++) - https://github.com/miek/inspectrum

Such Samples by Tim O'Shea - GR Based Sample Data File Visualization
https://oshearesearch.com/2015/05/22/such-samples-a-gnu-radio-tool-for-sample-data-visualization/
https://oshearesearch.com/2015/12/08/such-samples-2/

- Nate


> On Mar 19, 2016, at 11:05 AM, Henry Barton <address@hidden> wrote:
>
> So there’s no “read x samples, divide by y, do such-and-such, and you have a frequency-domain array” that I can average over time?
>
> Sent from Windows Mail
>
> From: Nikos Balkanas
> Sent: ‎Saturday‎, ‎March‎ ‎19‎, ‎2016 ‎1‎:‎31‎ ‎PM
> To: James Humphries
> Cc: Henry Barton, address@hidden
>
> Hi,
>
> I missed your second part. gr-fosphor is realtime, so It will follow whatever frequencies you have. Frequency hops show as frequency bands in a frequency spectrum.
> The frequency spread of a single plot, is your sampling frequency.
>
> HTH,
> Nikos​
>
> On Sat, Mar 19, 2016 at 7:22 PM, James Humphries <address@hidden> wrote:
> Hi Henry,
>
> There is a script, read_complex_binary.m, that is included with gnuradio. You can use that with Octave or Matlab to read the I/Q recordings from a file as a time vector.
>
> -Trip
>
> On Sat, Mar 19, 2016 at 12:43 PM, Henry Barton <address@hidden> wrote:
> Is there any simple formula for plotting spectrum (finding the intensity of each frequency component, Hertz by Hertz) from IQ recordings? Specifically I need to know how to read an IQ file and somehow dissect clusters of samples. I’ve written programs that deal with large amounts of data from files, so I think this shouldn't be too hard. I want to write my program so that it takes in a multi-hour IQ file and averages it like the 24-hour band averaging on the University of Twente WebSDR site. This would allow users to average an IQ file over time and see the most active frequencies and times. There’s no utility for this yet, and I’d like to write it and release it on my blog.
>
> On a side note: is it possible to go “frame-by-frame” in an IQ file? For example, to follow the hops of a 900-MHz FHSS device.
>
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