I have an AD9834. I make de PCB and all seems to be running in a correct way. I find an online calculator so I can probe different things with the SPI commands. The link is: http://designtools.analog.com/dt/ad98334/ad9834.html#troubleshooting
I tried 10Mhz, 20Mhz and 5.6 Mhz and all is correct.
for my surprise, when I tried a 400Hz sine wave, the DDS output doesn't go below 1Khz. The SPI sequence for a 400Hz sine wave obtained from the calculator is:
2100 4598 4000 8000 8000 C000 E000 2000 (Hex format)
I read the AN-1070 app, and i tried to make some hand calculation and I think that the calculator is correct too.
I also re-read the AD9834 datasheet to see if I missed something, but i could not see it.
Do you have an idea of what might be wrong ?