Dear Clive,
Could you please try to reproduce that with the reference design? Modify argument passed to GenerateWaveform16() in main.cpp to have the frequency you need. Let's see where that goes. There is also a function GetBufferFromFile() which called if LOADFROMFILE is defined in main.cpp. Typically this would search for a file called buffer1.txt and you can change that in the main.cpp also.
If you provide me with a FMC serial number I can look at the test report for that board.
I am attaching one buffer1.txt for your convenience. If you download Visual Analog from Analog Devices, a free tool, and you use the .vac attached you can display what the DAC buffer looks like. The same way you can display ADC buffers (adc0.txt, etc.). You could loop back ADC in to DAC out and visualize the buffer that way by simply running the application.
We need to figure out if spur is inherent to your design or not.
Best Regards,
Arnaud