Discuss-gnuradio mailing list
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On Wed, Jul 23, 2014 at 8:42 AM, Activecat [email protected] wrote:
Dear Sir,
I am learning to use the built-in “QAM Mod” and “QAM Demod” blocks.
Refer below flowgraph.The problem is, at the output of the “QAM Demod” block, I can’t get what I
fed into the “QAM Mod” block.
What is missing …?
All modulators take in packed bits and all demodulators output unpacked
bits. First, remember that there are filters involved, so there’s going
to
be a delay. You’d need to synchronize the output of the demodulator to
some
known word to understand which output bit is the correct start of the
data
stream. Easier would be to unpack the source data. Out of the ‘head’
block,
make another connection to a ‘unpack_k_bits’ block with an unpacking
value
of 8. Use this to compare to the demodulated bits.
Also, the vector source should generate values from 0 to 255 to create
the
packed bits needed as input to the modulator. Otherwise, you’ll just be
heavily biasing the constellation to just a few points. You can stick a
constellation display block on the output of the modulator to see.
Tom
On Wed, Jul 23, 2014 at 9:45 PM, Tom R. [email protected] wrote:
packed bits needed as input to the modulator. Otherwise, you’ll just be
heavily biasing the constellation to just a few points. You can stick a
constellation display block on the output of the modulator to see.Tom
Thank you very much.