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Re: [Discuss-gnuradio] DPSK mod/demod block work well?

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] DPSK mod/demod block work well?
Date: Thu, 31 Mar 2011 09:33:38 -0400

On Thu, Mar 31, 2011 at 9:07 AM, Songsong Gee <address@hidden> wrote:
I just made very simple dpsk mod/demod testing flow graph

you can see flow graph in following link: https://picasaweb.google.com/lh/photo/76z3sTbLs9Srz1N-wJhNzw?feat=directlink

When I run it, I found strange outcome from it: https://picasaweb.google.com/lh/photo/U0_S_71HzkL9t9RbeEBP2Q?feat=directlink

I didn't change any parameters in mod/demod blocks.

How can I get a good signal after mod/demodulation?

Well, the secret is that you really are getting good signals out of the demodulator, it's just not in the form that you think it should be.

The modulator takes in packed bits; that is, characters between 0 and 255. You are only giving it 0's and 1's. The output of the demodulator is providing you with unpacked bits, so each character represents a single bit. You will want to put an unpacked_to_packed block after the demod to put them in the same format as your input.

The reason why you are getting the zeros at the output is because a '1' in the input is really a '00000001' and a '0' is really '00000000', which is what you see in your sink.


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