Re: [Discuss-gnuradio] isolate channels from wideband

[Chris Kuethe]

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