Re: [Discuss-gnuradio] isolate channels from wideband

[Markus Heller]

Great! Thanks! I'm very curious!

br/vy73
markus
dl8rds

Am Freitag, den 31.07.2015, 14:34 -0700 schrieb Chris Kuethe:
> OK, I have a mostly working flowgraph and am now adding comment to all
> the blocks explaining why I'm doing this or that. Will publish tonight
> or tomorrow.
> 
> On Tue, Jul 21, 2015 at 11:56 AM, Chris Kuethe <address@hidden> wrote:
> > Maybe I'll do up an illustrated example on this using NOAA weather
> > radio, or the pager band
> >
> > On Tue, Jul 21, 2015 at 11:42 AM,  <address@hidden> wrote:
> >> I just use the built-in firdes stuff, rather than using an external
> >> designer.
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >> On 2015-07-21 14:38, Marcus Müller wrote:
> >>
> >> Hi Rich, hello Markus,
> >>
> >> On 21.07.2015 19:51, Richard Bell wrote:
> >>
> >> GNU Radio has channelizers built-in, but I've not used them yet, so I don't
> >> know how far they take you into this kind of task.
> >>
> >> the Polyphase channelizer is actually an implementation derived from that
> >> school of thought, and it works amazingly well.
> >> In fact, in preparation of a presentation at a certain ham conference, I
> >> tried using it to get 20 PMR/LPD channels out of a 1MS/s signal in real
> >> time, and then just shuffle them around, before feeding them back into the
> >> inverse synthesizer PFB.
> >>
> >> It's pretty easy:
> >> Design a single low pass filter, as if you just wanted to filter out the
> >> channel which is centered exactly at your RF center frequency, i.e. 0Hz,
> >> with the full sampling rate [2], using the gr_filter_design tool. Play
> >> around with the different window types[1], and bear in mind that the
> >> suppression outside your desired passband needs to be high enough so that
> >> the sum of the energy in all other channels don't hurt your channel too
> >> much, but don't overdo it (60dB suppression should be enough).
> >> Now you get a long filter. Copy and paste the filter coefficients from
> >> gr_filter_design to your PFB filter taps property.
> >> Set your channelizers number of channels according to your plans -- 40, if
> >> you want to get all the 40 25kHz channels in 2MHz. You get a block with 40
> >> outputs!
> >> Explaining things like channel mapping is best done by pointing you at the
> >> official documentation: [3]
> >>
> >>
> >> Greetings!
> >> Marcus
> >>
> >> [1] Hamming is not always the best choice, I'd try that, Blackman-harris,
> >> and Kaiser. I personally like harris in this case -- we want to get a full
> >> channel, two adjacent channels are usually not occupied, and as soon as we
> >> pass the stopband frequency, we're basically at -100dB.
> >> [2] assuming you want to use 2MS/s for your 2MHz wide band, 2MHz sampling
> >> rate, and assuming 25kHz wide channels, 12.5kHz cut off frequency, 25kHz
> >> start of stoppband. I get something like 440 taps.
> >> [3]
> >> https://gnuradio.org/doc/doxygen/classgr_1_1filter_1_1pfb__channelizer__ccf.html
> >>
> >> _______________________________________________
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> >> address@hidden
> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> >>
> >>
> >> _______________________________________________
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> >>
> >
> >
> >
> > --
> > GDB has a 'break' feature; why doesn't it have 'fix' too?
> 
> 
>