Question T3A04
From subelement T3 - T3A
What happens when antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?
Why is this correct?
Polarization mismatch between VHF/UHF antennas causes significant signal loss — up to 20 dB, equivalent to reducing a 100-watt transmitter to just 1 watt. When one antenna is vertical and the other horizontal, they can't efficiently transfer energy because the electric field orientations don't align. The other choices are incorrect: sidebands don't invert due to polarization mismatch, echo effects come from multipath propagation, and the signal reduction is quite significant.
Memory tip
Think of polarization like a mail slot — the letter must match the slot's orientation to pass through easily. Mismatched polarization creates a fundamental incompatibility in how electromagnetic energy transfers between antennas, making this principle apply to any VHF/UHF communication regardless of modulation type.
Learn more
VHF and UHF line-of-sight communications require careful attention to antenna polarization because these frequencies don't benefit from ionospheric mixing like HF signals do. Most repeaters use vertical polarization (matching handheld transceivers), while weak-signal operators typically use horizontal polarization for long-distance CW and SSB work. Understanding your local repeater's polarization helps optimize your frequency privileges within the amateur service.
Think about it
Why do you think polarization mismatch is much more critical at VHF/UHF frequencies than at HF frequencies where either vertical or horizontal antennas work equally well?