[Discuss-gnuradio] Help: QAM Constellation and PolyPhase Clock

[tom sutherland]

I have simple 16QAM Modulator block and am plotting the constellation with and without the a polyphase clock block . The constellation directly out of the modulator is not 16 "points" or even blobs but "random" looking points. I put it into a QAM Demod block and it demodulates it correctly. The constellation plot of the polyphase clock block shows  16 distinct "points" but when demodulated is quite noisy.

Can anyone explain:

1) Why is the output of the QAM Modulator block not show as 16 points?

2) Why would the "corrected" QAM Modulation not give better demodulation output?

I have attached the ConstellationQuestion.grc file.

Thanks...Tom

ContstellationQuestion.grc
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