I'm doing the baby steps right now to learn about GNU Radio Companion. I'm using 3.7.13.5 at the moment.

I'm just focusing on getting a simple binary stream together, such as '110100' (repeated) .... so it just goes '110100110100110100.......' and then to see whether I can generate a simple QPSK constellation map.

I don't yet understand exactly what to do in order to get that QPSK constellation map. But I've taken steps to string some blocks together - just to try something at least.

What I did was use a Vector Source block, that is set up at values '110100' (and this block is set to 'repeat' the pattern continually).

I then have a Chunks To Symbol block, where I arbitrarily have these following values for the Symbol Table [(-0.707 -0.707j), (0.707 -0.707j), (0.707 + 0.707j), (-0.707 + 0.707j)].

And then I have the QT GUI Constellation Sink block for viewing the constellation.

I know what I would like to do ----- but don't know what to do properly yet. But at least there are four points on the constellation diagram (as seen in the attached image).

May I ask what I need to do in order to get the Chunks To Symbols block to take in two bits at a time, in order to map each pair of bits to one of those four constellation points?

At the moment, I only have three unique combinations of bits .... which is 11 and 01 and 00 .... which can be seen in the pattern '110100'. So I'm just trying to get those three patterns to show up on the constellation diagram --- which should be three points on the constellation diagram (while the fourth point isn't encountered yet).

Could somebody help me by pointing out how the Chunks To Symbols block actually works? At the moment, if I purposely want to map the bit pair '11' to a particular constellation point - such as 0.707 + j*0.707, then is there a way to create that definition within the Chunks to Symbols block settings?

Right now, I don't actually know how the Chunks To Symbols block interprets the input data, and how it assigns various 'chunks' (which I assume are bit patterns) to each constellation point in the symbol map. That is, does this block look for various unique input patterns, and somehow links each unique input pattern to one of those values in the Symbol Map?

[![Chunks to Symbols][1]][1]

Thanks very much in advance! I'm very impressed with GNU Radio Companion and GNU Radio!

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**Update** - I found path for getting a constellation diagram. But haven't figured out how to use that properly yet as well. The other path is using a Constellation Object, where an online tutorial had this Symbol Map for the constellation : [0, 1, 3, 2] and the corresponding constellation points defined within the Constellation Object block are : [-1-1j, -1+1j, 1+1j, 1-1j]

But - as we can see, when I put a single value of '3' for the repeating Vector Source, I get multiple points in the constellation diagram spread out across a line, instead of a concentration of points around the point **1+1j**. Any nice recommendations on what I need to do to get on the right track? Thanks!

[![second image][2]][2]


  [1]: https://i.sstatic.net/MtDoC.jpg
  [2]: https://i.sstatic.net/mBY56.jpg