I’ve run into this sutuation.
While transmitting DC signal (I=const, Q=const) from TSG or digital interface, received signal (as measured by LimeSDR and external spectrum analyzer) have phase jumps, like in phase modulated signal.
Here is phase jump:
After I’ve changed TBB gain, this process started to alternate. For example, 1 second with multiple jumps, another second without jumps.
After running for a while, jumps completely gone.
Jumps after changing gain:
No jumps, after running for some minutes.
At first, it looked like some DAC bit is getting out-of-clock at digital interface.
But even using TxTSG problems remains.
Happened mutiple times, with different sample rates, different gains and at different frequencies (2 - 3 GHz band).