Polarization: Horizontal vs Vertical and Circular Satellite Signals
Satellite signals are polarised — the radio wave oscillates in a specific orientation. European satellites use linear horizontal/vertical polarisation; American ones often use circular. This is why your LNB has to be rotated.
Why Polarisation Exists
Two signals can share the same frequency if they are polarised differently. A horizontal channel and a vertical channel at the same frequency do not interfere. Polarisation doubles the number of transponders a satellite can carry.
Horizontal vs Vertical
The LNB has two internal probes, one horizontal and one vertical. The receiver selects between them by changing the supply voltage: 18 V for horizontal, 13 V for vertical. That is why half your channels vanish if one side of the LNB fails.
Circular Polarisation
Some satellites (especially American DBS) use right-hand and left-hand circular polarisation. The wave twists as it travels. These need a different LNB and are not interchangeable with European linear LNBs.
Why LNB Skew Exists
Because your dish is on a curved Earth, the horizontal/vertical axes of the incoming signal are rotated relative to your wall. The LNB skew rotates the internal probe to match. Get it right and both polarisations peak.
Telltale Signs of a Polarisation Problem
- All horizontal channels missing but vertical working (or vice versa).
- One polarity noticeably weaker than the other.
These point to an LNB with a failed side, or a receiver that is not switching voltage correctly.
Polarisation is the satellite's way of fitting two channels in one frequency slot. The LNB picks which one you want — and the skew aligns the picker.
