[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] DDC and Polyphase Channelizer

From: Jimmy Richardson
Subject: Re: [Discuss-gnuradio] DDC and Polyphase Channelizer
Date: Wed, 05 Jan 2011 17:14:29 +0800
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv: Gecko/20101207 Lightning/1.0b2 Thunderbird/3.1.7

Hi, Tom:

Please see my comments below.


On 1/4/2011 11:44 PM, Tom Rondeau wrote:
On Mon, Jan 3, 2011 at 11:25 PM, Jimmy Richardson<address@hidden>  wrote:
Indeed. Very strange. My guess is that there is a misconception
somewhere in the code about sample rate. I can't quite see it in my
head, but I'm guessing that the channel spacing isn't exactly the
channel spacing you think it is.
You mean the oversample rate O = N/i is wrong? As far as I can see, that's
the only number that could go wrong, since pfb_channelizer_ccf only takes 3
parameters, # of channels, taps and oversample rate, and it doesn't look
like the other two can be wrong.

I checked the calculation of O again, but couldn't find the problem. In the
Matlab code, harris uses loops "for nn=1:28:5600-28" to do the processing,
so it does seems a 28-to-1 downsampling in 40 channels.
No, not the oversample rate, just the sample rate. I'm thinking that
there is some misunderstanding somewhere about the actual sample rate
and the therefore the channel bandwidths such that the channels you
are pulling out are not covering the same frequencies that you think
they are.

Sorry, maybe I didn't get how the algorithm works, but it looks to me the actual sample rate does not enter into the equation, except in the filter generation part? If we use the same filter on both methods, then the actual sample rate should not cause the difference?

On the other hand, it could be a miscalculation in the
pfb_channelizer, although all of my tests with it came out fine.

Is the test cases included in the GNURadio source code? Also if I want to understand the logic inside pfb_channelizer implementation, are there any book or paper I should review besides harris' paper and book?

Have you looked at the examples in gnuradio-examples/python/pfb?
Specifically, channelize.py, chirp_channelize.py, and synth_to_chan.py.
I checked the first two samples when I wrote the channelizer, although it
seems they didn't use the oversample rate parameter. I couldn't find the
last one (synth_to_chan.py) though.

The synth_to_chan.py is not in the tarball release. It was introduced
a little while ago when I added the synthesis filterbank. You'd have
to get it from the git repo.

Ok, I'll take a look.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]