Single output LNBFs will only output one polarity at a time. What does that mean and why is this important? Anytime one of the connected STB's selects a channel on a horizontal polarity, all STBs will only be able to receive horizontal polarity transponders on that satellite. This is because the single port will switch to the polarity of the highest selected voltage (Horizontal = 18Vdc). If all channels on that satellite are on one polarity, this will not be a problem.
On a regular satellite system using non-bandstacked LNBFs, if you wish to send satellite signals from both polarities to all STBs, then the LNBF must have two outputs and the switch must have two inouts per satellite position (13vdc for vertical / 18Vdc for horizontal polarity). A legacy DirecTV multi-switch is typically used. Best if it is a powered switch, rather than a passive switch.