I am attempting to transmit a tone at frequency Fc with the AD9361 where I create IQ data using a DDS where the I data is a cosine function and Q data is a sin function. The spectrum of my transmission shows the tone generated at F(LO) +/- Fc. I'm expecting that it will only show up at F(LO)+Fc. I suspect that the Q data in my TX data path is not getting through to the AD9361 somehow or that the AD9361 is configured to disable the Q data path?? I've tested this by switching the I and Q data on and off independently. Switching Q has no effect while switching I turns the signal on and off. I'm pretty certain my data path from the BBP to the AD9361 is designed correctly because it works just fine for receive mode. I'm using 2R2T, DDR, TDD, DUAL PORT timing. The only thing that I'm doing differently from the diagram in UG-570 is that I set TX_FRAME to a constant high value when I transition into transmit mode. I believe this is supported as a "burst" frame. Perhaps this is the issue? I'm not sure I really understand the purpose for TX_FRAME since the channel 1 and 2 data words are clocked in on different edges of FB_CLK. I would appreciate any help on this.