Forum: GNU Radio Simple QPSK baseband transmission using GRC

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Jérémy Skelton (Guest)
on 2008-12-04 22:12
(Received via mailing list)
Hi,

I have been trying to make a baseband transmission by assembling
blocks with GRC.
I'm using this scheme :
http://www.skelton.eu.org/Image1.png

To problem is that I'm not able to recover the original data but only
the repetitions of it : I repeat several times two bytes in the input
file and I get several two other bytes at the output.

Any idea to solve this ? Is it possible that the decoding block takes
a bad phase (maybe due to quadrature demodulation)? If so, what block
can I use to make the phase correction ?

Thanks,
Jérémy
Johnathan C. (Guest)
on 2008-12-05 01:32
(Received via mailing list)
On Thu, Dec 4, 2008 at 12:11 PM, Jérémy Skelton 
<removed_email_address@domain.invalid>
wrote:

> To problem is that I'm not able to recover the original data but only the
> repetitions of it : I repeat several times two bytes in the input file and I
> get several two other bytes at the output.

It looks like you have the endianess wrong.  The DBPSK modulator works
MSB to LSB on the incoming bytes, while your demodulator is packing
the bits back into bytes LSB to MSB.

-Johnathan
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