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Re: [Discuss-gnuradio] Getting really confused by PSK mod/demod blocks


From: Marcus Müller
Subject: Re: [Discuss-gnuradio] Getting really confused by PSK mod/demod blocks
Date: Tue, 2 May 2017 17:42:50 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0

Hi Pierre,

really odd looking data – what's that? have you tried comparing your unpacked bit streams? it's possible you're just missing the first few bits at the beginning, but if you then reassemble the bits to octets, you'd get wrong data.

Best regards,

Marcus


On 05/02/2017 05:28 PM, Pierre AVITAL wrote:
Hello,

I've been trying to use the PSK mod/demod, as well as DPSK mod/demod, blocks to try to listen to signals using DQPSK modulation.
But I'm completely stumped by their behavior : as can be seen in the attachement here, I've tried to simulate my demodulation by having a byte-stream sent through either DPSK or GFSK modulation, then demodulating it and repacking it before sending it to a block I coded that just prints what's on input and signals whether or not it could spot a sync word.

This works fine with GFSK, where the output of my "Test Block" is the same as what the file contains.
But with DPSK, I get really odd looking data. Is there something I'm missing here ? I've been trying various repackings both before and after mod/demoding the signal, and have yet to figure out how to get my data demodulated (or even modulated) properly with the PSK blocks. 

Thanks in advance for any help you could provide.


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