On Wed, Feb 24, 2016 at 8:01 PM, tom x <tomx4...@gmail.com> wrote:
> 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
>
Take a look at the link and paper that I mentioned. It sounded like you
think that the channelization should be something like the following,
assuming a 4 channel channelizer:
| ch2 | ch3 | ch0 | ch1 |
| | |
| |
-f/2 ------------ -f/4 ------------ 0 ------------ f/4 ------------ f/2
When the channelization is really:
ch2 | ch3 | ch0 | ch1 | ch2
| | | |
-f/2 ------------ -f/4 ------------ 0 ------------ f/4 ------------ f/2
So channel 0 spans DC. You had offset the channel from 0 to f/4.
And because we're at complex baseband, channel 2 wraps around from +f/2 to
-f/2
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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