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Re: [Discuss-gnuradio] hi all, can I use one RX receive a wideband signa


From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] hi all, can I use one RX receive a wideband signal and then seperate it to many narrowband signals
Date: Thu, 23 Dec 2010 01:49:00 -0500

On Thu, Dec 23, 2010 at 1:19 AM, James Jordan
<address@hidden> wrote:
> Hi Martin,
> pfb_channelizer_ccf will seperate all channels, But I dont need each
> channel.
> I only need the channel I am interested in. Seperating all channels will eat
> a lot of CPU resource.


Not really. It's a very efficient algorithm and won't cost you that much.


> I have check pfb_channelizer_ccf source, it finally use fftw to process
> channelizer.
> So can I directly use fftw to do my work.

Not quite. The PFB channelizer uses a filterbank where each filter is
specifically generated with a phase relation. The FFT part isn't doing
exactly what you expect it's doing. We'd have to go through the math,
though.

If you are looking to just get a single channel out, then use the
pfb_decimator_ccf(N, taps, channel) to split the bandwidth into "N"
channels, using filter taps "taps," and you can specify which channel
you want to take by specifying the "channel." Here's the way to
translate the "channel" into the physical Nyquist zone you are looking
for N=7 (hopefully this format survives):

Channel:      4        5        6      0       1       2       3
Frequency: -3B  |  -2B  |  -1B  |  0  |   2B  |  2B  |  3B

Tom


> On Tue, Dec 21, 2010 at 6:19 PM, Martin Braun <address@hidden> wrote:
>>
>> On Tue, Dec 21, 2010 at 06:02:44PM +0800, James Jordan wrote:
>> > Hi all, I need to receive many narrowband signals, but usrp hard ware
>> > only
>> > provide 4 RX,
>> > so I need to receive more than one narrowband signals per RX. Is my idea
>> > possible?
>> > I dont want to use more than one usrp to achieve that, anyway which will
>> > be an
>> > option if my first idea can't work.
>>
>> If your total bandwidth (sum of all bandwidths) does not exceed a couple
>> of MHz, you can use the polyphase channelizer (pfb_channelizer_ccf).
>> The result will be an equally spaced set of narrowband channels.
>>
>> Happy DSP'ing,
>> MB
>>
>> --
>> Karlsruhe Institute of Technology (KIT)
>> Communications Engineering Lab (CEL)
>>
>> Dipl.-Ing. Martin Braun
>> Research Associate
>>
>> Kaiserstra├če 12
>> Building 05.01
>> 76131 Karlsruhe
>>
>> Phone: +49 721 608-3790
>> Fax: +49 721 608-6071
>> www.cel.kit.edu
>>
>> KIT -- University of the State of Baden-W├╝rttemberg and
>> National Laboratory of the Helmholtz Association
>>
>>
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