Forum: GNU Radio Simple Digital Mod Problem

Im a total newbie to GNURadio. So my plan was to simply test a digital
modulation path, without channel. Then compare input file and output 
file.
The input file was a previously captured random file through GNURadio. 
But
the problem is, that the output file is about 8 times bigger and clearly 
not
the same!
Any help :)?
<http://gnuradio.4.n7.nabble.com/file/n38857/grc.png>



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The output of the demod is unpacked, that is, only one bit in each
byte is used.  Place an unpacked_to_packed block before the sink and
you will have more luck, however you will still get an offset in the
byte boundaries between the input and output.

Ben

Thanks! I see now what you mean, but how can i get rid of these boundary
mistakes? The Result is similar to the original, but the bytes are kind 
of
"shifted". So from a "FF 00" results a "FE 01"..



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Take a look at the packet_encoder and packet_decoder blocks.  The
encoder adds a header to the packet, so that the decoder can
synchronise to it, and get the correct byte boundary.  The
implementation (in the current master branch) is found at
gnuradio/grc/grc_gnuradio/blks2/packet.py.

This is actually what i would like to do later by hand. Isnt there a
possibity how i can fetch the raw bits or bytes directly after 
receiving?
Sorry if its a stupid question..



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I don't understand you're question.  What do you mean by fetch the raw
bits or bytes?  It seems that you are already doing that fine with
your file outputs.