Re: Combined constellation modulator/Decoder do not seem to work

Hi Mike,

Again, thanks for the great help and sorry to bother you again. 

The Polyphase Clock Sync seems to have serious problems. It works well at 2 sps, but does not work for 4 or 8 sps. I replaced it with the recommended Symbol Sync block, which appears to work at the different sps based on constellation plot observations. However, when I tried to test the validity of its output against the input data, I couldn't find any delay to get a match. So I am left wondering if it is working well???

Any suggestions?

Thanks!

George

On Fri, Mar 12, 2021 at 8:23 PM Mike Markowski <mike.ab3ap@gmail.com> wrote:

Hi George,

You used differential encoding but forgot differential decode.  I added
the block in the attached.  (I disabled your file creation and displayed
to gui, easier for me to check.)

Little things are the hardest to spot.  :-)

Mike Markowski

On 3/12/21 4:46 PM, George Edwards wrote:
> Hi Mike,
>
> Thanks for your help!
>
> As I mentioned in my email, my flowgraph consists of some of the blocks
> in the example. I dropped some of the blocks because I am doing concept
> testing to ensure I know how to set parameters for the blocks. In
> terms of delays, that is not a problem. I am dumping the outputs into 2-
> file sinks, so in post processing I can compensate for that. The problem
> is that the tx and rx data are not the same, so I am missing in setting
> parameters.
>
> Thanks again!
> George
>
> On Fri, Mar 12, 2021 at 3:31 PM Mike Markowski <mike.ab3ap@gmail.com
> <mailto:mike.ab3ap@gmail.com>> wrote:
>
>     I can't make out details in your image, George, but attach one I made
>     when working through the tutorial and works just now under gnuradio
>     3.8.1.0.  Like someone else mentioned in another reply, I found the
>     delay to be 58 and set it as the default in the attached flowgraph.
>     Zoom in on the bit stream plot and allow a second or two after changing
>     delay to see the effect.
>
>     Hope this helps,
>     Mike Markowski
>
>     On 3/12/21 10:37 AM, George Edwards wrote:
>      > Hello,
>      >
>      > I cannot get the combined Constellation Modulator/Decoder as
>     shown below
>      > to work. The figure below is an example from the online Guided
>     Tutorial
>      > PSK Demodulation.... I leave out the Equalizer, Costas Loop
>     blocks, the
>      > channel was set to pass the signal unimpaired and the Poly Clock
>     Sync
>      > was set for Output sps=1. The constellation plot of the output of
>     the
>      > Poly Clock Sync is perfect. Now, in the flowgraph below, the signal
>      > entering the Constellation Modulator and that leaving the
>     Constellation
>      > Decoder are routed into Time Sinks for display. I route these
>     signals
>      > into File Sinks so I can print them and compare 1's and 0's. The
>     results
>      > show they are not the same. I passed Constellation Rect.Object
>      > parameters to both the Constellation Modulator and Decoder, which
>     seems
>      > logical to me, but I could be wrong???
>      > Will appreciate any help you can provide because what enters the
>      > modulator should be the same as what is leaving the demodulator.
>      > Regards,
>      > George
>      >
>      > image.png
>