It's a constellation plot for sure - says it right on the block in the PNG, but it's all internally generated anyway. There should be 1 perfect phase, then 3 out of phase points. No noise - no phase/frequency offset. Timing shouldn't be an issue here even if it were a normal plot.
I think the issue is no matched filter on the other side. RRC filtering won't look very appealing to the eye, but RC filtering should match what you expect. Try adding a matched RRC filter before you do the constellation. You should see the 4 samples/symbol and their trajectories as they converge onto the 4 nice points. Brian On Wed, Jan 14, 2015 at 2:51 AM, Martin Braun <martin.br...@ettus.com> wrote: > On 01/14/2015 04:56 AM, Salman Dinani wrote: >> Hi to all, >> >> I am a beginner in using GNU radio(GRC). I have made a DQPSK transmitter >> using the blocks of GNU radio (attached Figure QPSK_1). when I connected >> the constellation plot with it, It gave me the a very scattered >> Constellation Plot Instead of four Clean Constellation Dots (attached >> Figure QPSK_2). I have checked with all forms of signals but the >> constellation remains distorted.(i.e. vector source, signal source etc.) >> >> Is it normal plot or am I missing some thing? Kindly help. > > My guess is yes, it's a normal plot, and you have no time sync in there. > > M > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio