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: discuss-gnuradio@gnu.org
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 <kw...@outlook.com> 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, discuss-gnuradio@gnu.org
>
> 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 <james.humphr...@ettus.com>
> 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 <kw...@outlook.com> 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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