On 31/10/14 00:44, Ian Jackson wrote:
In message , Ralph
Mowery writes

"Ian Jackson" wrote in
message In
the UK, would you be wanting to rotate it for TV? Don't forget that
one type of antenna used in the very early days of BBC TV (Channel 1,
vertical, 45MHz) was a 'sloper. This was an off-centre-fed wire dipole,
with the short leg being a quarterwave, and attached as high as possible
(maybe to a chimney or a gutter). The other leg was an odd number of
quarterwaves, and attached much lower down. As a result, the antenna had
one of its major lobes sort-of off the end (say 30 degrees off the
wire),
in a more-or-less horizontal direction, and responding well to
vertically
polarized signals.
--
Ian

I have not kept up with TV signals for a long time. In the US they
started
off as all horizontal. I think that some may have gone to circular,
but not
sure. It might be the FM stations I am thinking about. Not sure what
they
are using now on the digital signals.

What are they using in other countries ? Horizontal, vertical ?

Historically, both. The very first UK TV transmitter (45MHz), launched
in 1936, was vertical. This closed down swiftly on 1 September, 1939,
and WW2 started two days later.

After WW2, TV resumed in 1946. Four more channel frequencies (all BBC
only in those days) were added throughout the country in the Low Band
(Band 1, as we call it), and the split of vertical and horizontal was
around 50/50. In 1954, the independent network (ITV) arrived, all in the
High Band (Band 3) - again with around a 50/50 split.

In 1963 (?) UHF was launched - initially carrying only a second BBC
channel, on 625-lines. Eventually, this expanded to four - and in some
places - five channels, all transmissions being co-sited - or almost
co-sited (so that only one, fixed antenna was required). Without
exception, all high(er) power analogue transmitters were horizontal, and
almost without exception, all the low(er)-power fill-in relay stations
were vertical. Although these days it's all digital, same pertains -
except for (I think) one new fairly high power directional vertical
transmitter.

BTW, the old 405-line VHF network was totally closed down in the 1980s.
Although VHF is no longer used for TV, part of the Band 3 allocation is
now digital radio - all vertical. FM was originally all horizontal, but
gradually the benefits of circular - and the simpler mixed -
polarizations became implemented. Very few are now purely horizontal.

Other European countries have had a somewhat different history, but I'm
pretty sure that very few TV transmitters were/are vertical - except for
local fill-in and low power. For FM, the Irish Republic has always
(sensibly) used vertical.

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.

The convention for UHF TV stations in the UK was for high powered "main
stations" to use HP and low power relay stations to use VP. This cross
polarisation provided about 26dB protection against co-channel interference.

--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk
..
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