LimeSDR applying reference clock

[mzs]

The answer was at the bottom of the thread that I linked to:

About the clock output of limesdr

It was left NF just to minimize probability of spurs when it is not connected, i.e. just not to have one more antenna Actually we do not observe any additional spurs when R151 is soldered on. But I would leave it as it is if you do not plan to use it.