Re: [Discuss-gnuradio] Channelizer mapping

[John Ackermann N8UR]

Thanks.  I got some off-help list (thanks, Noah!) and think I have it 
sussed.  There is a trick, though: if you have an even number of 
channels, one of them will wrap from the right side of the graft to the 
left, and be useless.

So as a practical matter, you might as well design for an odd number, 
and then the channel map to get frequency-order has 0 at the center, 
counting up on the right side from 1 to int(n/2), counting down on the 
left side from n-1 to int(n/2)+1.  So for n = 7 (seven channels):

[ 4,5,6,0,1,2,3 ]

I hope I stated that correctly, if not someone please correct me.

(My earlier example was based on the mistaken assumption that you had to 
"waste" a channel for an odd number, so I had 8 channels, and tossed one 
to get 7.  Backwards.)

John
----

On 06/02/2017 04:32 PM, West, Nathan wrote:
> It works kind of like an fftshift. The center channel is 0, the lowest
> channel is nchannels/2 + 1 or so... I think your mapping could have 4 on
> the end to get the whole sequence.
>
> On Fri, Jun 2, 2017 at 11:25 AM, John Ackermann N8UR <address@hidden
> <mailto:address@hidden>> wrote:
>
>     Is there a basic rule for how to assign channel numbers to the PFB
>     channelizer output?  I seem to be too dense to figure it out from
>     the docs.  I just want to pull the channels out in order of their RF
>     frequency, low to high.
>
>     I currently have a 7 channel channelizer which seems to work
>     properly after I farted around to get this map: [5,6,7,0,1,2,3]
>     using a "Channels" value of 8 (note that channel 4 is thrown away).
>
>     Now I want to extend the number of channels, and the number may be
>     even or odd.  From Tom Rondeu's tutorial, I get the sense that the
>     mapping changes based on even or odd channel count.
>
>     Is there a basic rule to develop the map for the case of RFch0 =
>     ch0, RFch1 = ch1, etc.?
>
>     Thanks,
>     John
>
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