I am trying to use gnu radio to transmit data from one SDR to another using a 16QAM modulation scheme. This is the diagram on the receiver side.

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Looking at the constellation sink, the constellation will not resolve. Every once in a while, it briefly looks like it comes close to the standard 16QAM constellation but falls apart. I do not think that multipath is the culprit here. The antennas are very close to one another. I expect it to be some sort of timing issue.

I am confused about the parameters in the Constellation Receiver block. What is the "loop bandwidth" parameter? What does it change and what is the most common range of values used for it?

I am also confused about the maximum and minimum frequency deviation parameters. A general description of what these change would be helpful. The documentation says these values are the maximum and minimum "normalized" frequency values. What are the frequency values normalized to? Does maximum frequency deviation mean the maximum allowed mismatch between the transmitter and receiver local oscillators?



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