On 31/10/14 18:19, Frank Turner-Smith G3VKI wrote:
VHF FM radio was indeed horizontally polarised at first, and was aimed
at fixed receivers with rooftop aerials. I believe horizontal
polarisation (HP) was first chosen in an attempt to provide greater
coverage than vertical polarisation (VP). AIUI, over a distance from the
TX, a VP transmission twists toward HP as it "grazes" the curvature of
the Earth. In doing so energy gets absorbed and the signal is
attenuated. The arrival of FM car radios meant a growing number of
listeners were using vertical antennas so a change to slant or circular
polarisation was introduced.

http://www.bbc.co.uk/rd/publications/rdreport_1960_16

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73 de Frank Turner-Smith G3VKI - mine's a pint.
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