Refuse to set out-of-range downsampling frequencies.
Remove some debug output.
Don't fall over if two consecutive batches happen to set entirely identical register values.
Simplify the PLL mix_div / div_num calculation, and make sure we don't fall out of the
loop with div_num unset.
Set RF mux based on target frequency, not LO frequency.
Better selection of PLL/LO frequencies near the edges of the tuning band.
Decrease vco_min a little as it still seems stable there.
Set the image rejection filter correctly based on whether we are doing
high-side or low-side mixing.