I just finished my AD9954 board and I'm getting spurs on audio frequencies. I haven't been able to test the board with spectrum analyzer since there's no hams around with one...
You can see the problem at: http://www.saunalahti.fi/johku76/pic/spurs.jpg Pictures of the project can be found www.oh1gtf.com First quick note about the DDS setup: I'm in the process of building a 425MHz reference oscillator, but since it's not finished, I'm using only a 50MHz crystal "can" oscillator and 4 X multiplier on the DDS. So, this way I'm having a 400MHz system clock. In the picture above, the antenna is not connected. Some kind of leakage can be detected, since when I connect the antenna some of the "spurs" disappear. By the way, some of the spurs, which don't disappear when connecting the antenna, don't have image rejection, so they are both visible on the screen, getting away off from the zero beat when adding frequency from the DDS. Some times when going with 1 Hz steps the "spurs" kind of jump in and disappear with every Hz. Is those audio frequency spurs a result from bad IQ signal or some kind of imbalance, or am I just having problems with grounding loops etc? 73 Janne, OH1GTF
