Ian Jackson wrote:
In message , Jeff Liebermann
writes
On Sun, 17 Nov 2013 22:26:53 +0000, Channel Jumper



This is the reason why television is horizontally polarized.

TV is horizontally polarized because the first FM operated in the
42-50 MHz region, where horizontally polarized antennas were more
common. A vertically polarized 30 MHz Yagi would be quite
impractical. The first TV stations were 44-50 MHz, and later moved to
50-56 MHz. Same problem... a vertical Yagi would be too big. There
are some other reasons if you want more detail.

In the UK, we longer use VHF (low-band and high-band) for TV (it's all
now on UHF). However, when we did, around 50% was vertical and (of
course) 50% was horizontal. The very first BBC transmitter (in London,
opened in 1936) was actually vertical, on 45MHz (they were rather big,
especially at ground level!), and remained so until VHF closed in the
late 80s. With only one or two exceptions, all high-power UHF is
horizontal, but quite a few lower-power fill-in transmitters are
vertical (to minimise mutual interference).

Here in the Netherlands, all TV and FM radio started out horizontally
polarized. The first transmitters were on VHF and newer ones on UHF,
but all horizontal.

However, at the "digital switchover", all transmitters were changed to
vertical polarization (at considerable effort and expense, swapping the
antennas in high towers using helicopters etc).

FM radio had been converted to vertical polarization a decade or so
before that. I think it was all done because it is so much easier
to have a vertically polarized omni antenna, and the general trend
is towards many small local transmitters which are of course received
from different directions, instead of/in addition to the existing network
that consisted of a small number of very high sites typically received
using yagi antennas.
Car radio antennas are also vertically polarized and are at a disadvantage
receiving horizontally polarized FM radio.

Rob wrote:


Car radio antennas are also vertically polarized and are at a disadvantage
receiving horizontally polarized FM radio.

Exactly why so many commercial transmitters are circularly polarized...