Modulation Toolkit Error 21856

Updated Apr 4, 2018

Reported In


  • USRP Software Defined Radio Device


  • Modulation Toolkit

Issue Details

  • I'm using Modulation Toolkit and am receiving Error -21856, but the Modulation Toolkit VIs aren't telling me what this error means or where it's coming from. Why is this?
  • I'm using the Modulation Toolkit and am receiving Error -21856: Invalid constellation; Unable to find max length symbols in quadrants 1 and 4 to calculate quadrature skew. Why am I getting this error?


Many of the Modulation Toolkit VIs have Allow debugging? unchecked in VI Properties for optimization purposes, so they will not pass detailed error information. You can change this by going to File >> VI Properties, changing the Category to Execution and unchecking this option.

This error indicates the Modulation Toolkit VIs are not able to process the given symbols properly. This can happen if you've set your modulation to a different scheme than your actual signal, if there is a large amount of noise, or other instances that corrupt the received signal. These conditions generate an error because the calculated values under these conditions can be erroneous.

Additional Information

You can specifically monitor for this error using the Clear Errors VI and modify your program to account for this situation.


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