Re: [Discuss-gnuradio] isolate channels from wideband

[Chris Kuethe]

OK, Here it is... at least, a beta version.  I have yet to come up with a concise explanation of the channel map and why you'd want to oversample, but it is functional.

This flowgraph would work equally well by directly connecting all the ports together, but I'm a big fan of using virtual sources and sinks to make the design somewhat self-documenting..

 

On Sat, Aug 1, 2015 at 4:55 AM, Markus Heller <address@hidden> wrote:

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
> >>
> >> _______________________________________________
> >> Discuss-gnuradio mailing list
> >> address@hidden
> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> >>
> >>
> >> _______________________________________________
> >> Discuss-gnuradio mailing list
> >> address@hidden
> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> >>
> >
> >
> >
> > --
> > GDB has a 'break' feature; why doesn't it have 'fix' too?
>
>
>

--

GDB has a 'break' feature; why doesn't it have 'fix' too?

pfb_channelizer_demo.grc
Description: Binary data