How does 13V/18V polarization switching work?
Satellite receivers select LNB polarization by changing the DC voltage they send up the coaxial cable: 13V selects vertical (or right-hand circular) polarization, and 18V selects horizontal (or left-hand circular) polarization. Inside the LNB, this voltage switches between two probes or the appropriate front-end path aligned to each polarization. This lets a single cable carry the polarization command alongside the signal and LNB power.
Satellites transmit two polarizations on overlapping frequencies to effectively double capacity, and the LNB must select only the desired one to avoid interference. The 13/18V scheme is a simple, universal way to make that choice without any extra wiring.
Combined with the 22 kHz tone for high/low band selection, these voltage levels give the receiver full control over which of the four possible sub-bands (low/high x vertical/horizontal) the LNB delivers. Because the voltage must be accurate at the LNB after cable losses, long cable runs sometimes require the receiver to boost to about 14V/19V, and severely undervoltage lines can cause the LNB to fail to switch to horizontal polarization.