On Wed, Jan 14, 2015 at 8:50 AM, Brian Padalino <bpadal...@gmail.com> wrote:
> 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 Yes, indeed, Brian is correct. The modulator block uses an RRC pulse-shaping filter that also interpolate to some number of samples/symbol. So what you are seeing is due to the ISI (inter-symbol interference) as a result of the RRC filter. Applying a matched RRC filter will remove (most of) the ISI. Tom > 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 >
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