Is that actually possible or the chip is really programmed internally for 150MHz to yield an output at 300MHz?
Just because the Si5351 is not specified for 300MHz does not mean that
most cannot be overclocked to generate 300MHz fundamentals.
Normally harmonics are a nuisance and they can degrade the bridge measurements without adequate filtering.
How does the software avoid these errors?
Michael Knitter uses the same Si5351 with a weaker processor in his FA-VA5.
Some relevant DSP magic is described around 11:30/30:01 here:
Oristo