Thanks for the reply, Could you please clarify what you mean by 'you're offsetting the frequency and shouldn't be'? I am tuning the frequency of the USRP, but other than that I am not sure what you mean. The channelizer flow graphs in the link set the Ch0: Center Freq field as well. Thanks, Tom
On Sun, Feb 21, 2016 at 4:11 PM, Tom Rondeau <t...@trondeau.com> wrote: > On Sat, Feb 20, 2016 at 12:43 AM, tom x <tomx4...@gmail.com> wrote: > >> Hi, >> >> I am working on an application to capture IEEE 802.15.4 traffic on >> multiple channels simultaneously. (I will mention now that I am new to GNU >> Radio and DSP.) I can successfully capture on one channel. I read the 2009 >> paper "Multi-Channel IEEE 802.15.4 Packet Capture Using Software Defined >> Radio", where L. Choong is able to capture traffic on four channels >> simultaneously with four frequency translation and FIR filter blocks. I >> have tried this approach with two channels but did not have success, most >> likely because the parameters to my filters were incorrect. >> >> This mailing list's archives pointed me to the polyphase channelization >> block, which I think can simplify this task. Here is a link to a picture of >> my flow graph: >> >> http://i.imgur.com/sxQnEIw.png >> >> I am tuning the USRP to halfway between channel 25 and 26 (whose >> corresponding frequencies are shown in the picture). Each channel is 2MHz >> wide, and the center of each channel is separated by 5 MHz. With this in >> mind, I set the USRP's bandwidth to 7MHz, which would contain channels 25 >> and 26 (Is setting this parameter necessary? I would like to scale this >> design up to four channels.) >> The 'target_rate' is the width of a channel, so I am setting the >> frequency cutoff to half of that, assuming the signal I want would be >> centered about 0 Hz. I set the transition window to less than half of the >> sample rate, on the advice of this blog: >> http://blog.kismetwireless.net/2013/08/hackrf-pt-2-gnuradio-companion-and.html >> . However, no packets are making it to the sinks, when I transmit on either >> channel from a separate radio. Does anything about this set up jump out as >> incorrect? I would appreciate any tips you could offer. >> >> Thanks, >> Tom >> >> > > Tom, > > This might help you out: > > > http://www.trondeau.com/examples/2014/1/23/pfb-channelizers-and-synthesizers.html > > One issue is you're offsetting the frequency and shouldn't be. Channel 0 > spans -B/2 to +B/2 (B being the bandwidth of the channel) and centered > around 0. There should be images in the link (or the paper it references) > that should show this. > > Tom > >
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