New QTGUI Eye Sink proposal

[Christophe Seguinot]

Hi

I developed a QTGUI eye sink block for GRC and hope it will be interesting for the community. I will soon submit it as a pull request. The code was tested on the latest master branch (gnuradio 3.9) but it may be easily merge in 3.8 (I did 't tested it on 3.8).

I really want to congratulate developers for their good quality code of GNURadio. Without that I wouldn't have been able to develop this eye_sink.

The eye sink has been written starting from a raw copy of the time sink code:

• all time sink functionalities have been kept except some unusefull ones such as stemplot and xAxis scaling
  
• each eye_sink block handles several input streams,
  
• each single stream eye pattern is plotted on a separate QwtPlot
• eye length is fixed at 2 symbol time.
• each stream is used to displays all available subset of length 2 symbol time found in the input stream
• this requires that the symbol rate be an integer multiple of the sample rate.
  
• triggering is identical as time_sink

Il must be noticed that a real eye diagram would be triggered with  a (recovered) symbol clock. For these reasons, triggering of noisy and/or unsynchronized (receiver) signals is tricky and may lead to incorrect eye pattern

Regards, Christophe