I'm hoping someone can enlighten me. I frequently see Yagi antennas mounted
on commercial buildings. They are usually relatively simple, probably mono-
band units, aimed at the horizon. What's puzzling is that many of these
tend to be polarized *not* vertically or horizontally, but at a 45 degree
tilt! Can anyone explain that?

(I know nothing about the specific busineses or the purpose of the antennas,
so I can't speculate about what's at the other end of the radio signal).

Bob, KI8AB

(remove 'duct tape' to respond)

"Robert Lyons" wrote in message
...
I'm hoping someone can enlighten me. I frequently see Yagi antennas
mounted
on commercial buildings. They are usually relatively simple, probably
mono-
band units, aimed at the horizon. What's puzzling is that many of these
tend to be polarized *not* vertically or horizontally, but at a 45 degree
tilt! Can anyone explain that?

(I know nothing about the specific busineses or the purpose of the
antennas,
so I can't speculate about what's at the other end of the radio signal).

Bob, KI8AB

(remove 'duct tape' to respond)
To have some signal for both Horizontal and vertical.

They are usually for the reception of background/storecasting music from
a broadcast FM station. Regards, Sparks

In some cases the fixing nuts and bolts have come loose.

My next door neighbour's TV antenna was hanging off the chimney for years
with perfectly satisfactory reception.

I've never had an outside TV antenna. A length of wire hanging out of the
socket on the back of the receiver always worked for me until the cotton
curtains were replaced by aluminium venetian blinds.

A polarisation error of 45 degrees of a dipole results in only 3 dB smaller
signal. This is not noticed in areas of good signal strength where most
people live. Polarisation doesn't seem to bother mobile phone users very
much either.

It is necessary only that interfering signals and echos, if there are any,
are minimised. And that depends more on the direction from which waves are
received.
----
Reg.

Many, if not all, FM broadcast stations in the US transmit both a vertically
and horizontally polarized signal. So, rotating the antenna 45 degrees is
not giving up anything. You also see other fixed direction VHF antennas on
businesses, that have nothing to do with broadcasting.

Tam/WB2TT
"Reg Edwards" wrote in message
...


A polarisation error of 45 degrees of a dipole results in only 3 dB
smaller
signal. This is not noticed in areas of good signal strength where most
people live. Polarisation doesn't seem to bother mobile phone users very
much either.

It is necessary only that interfering signals and echos, if there are any,
are minimised. And that depends more on the direction from which waves
are
received.
----
Reg.

Tarmo Tammaru wrote:
Many, if not all, FM broadcast stations in the US transmit both a vertically
and horizontally polarized signal. So, rotating the antenna 45 degrees is
not giving up anything.

It's giving up 3 dB. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Many, if not all, FM broadcast stations in the US transmit both a
vertically
and horizontally polarized signal. So, rotating the antenna 45 degrees is
not giving up anything.

================================

Simultaneous transmission of vertical and and horizontal polarised signals
from a single antenna system is impossible without upsetting the desired
radiation coverage pattern.

What you mean is your clever US broadcasting engineers have designed
antennas which radiate "Circularly Polarised" signals.

As Cecil says, nobody gains anything power-wise. For the same transmitter
radiated power everybody's signals are 3 dB down (half-power) relative to
simple linear polarision when both transmitting and receiving antennas have
the same polarisation.

The advantage of circular polarisation is that it doesn't matter which
polarisation your antenna is orientated because, in practice, when erecting
it, the polarisation received by your antenna is usually a matter of
guesswork anyway.

Only with relatively-rare, direct line-of-sight broadcasting propagation is
there any certainty in the polarisation of received signals.
----
Reg.

"Reg Edwards" wrote in message
...
Many, if not all, FM broadcast stations in the US transmit both a
vertically
and horizontally polarized signal. So, rotating the antenna 45 degrees
is
not giving up anything.

================================

Simultaneous transmission of vertical and and horizontal polarised signals
from a single antenna system is impossible without upsetting the desired
radiation coverage pattern.

What you mean is your clever US broadcasting engineers have designed
antennas which radiate "Circularly Polarised" signals.


If you go to a broadcaster's web site, they will say X KW horizontal, and X
KW vertical, with no reference to right or left hand polarization. I take
that to mean cross polarized, rather than circular. Obviously, the reason
for the vertical component is car radios. As for messing up the pattern, I
would think that in the majority of cases they want equal propagation in all
directions

Tam/WB2TT
As Cecil says, nobody gains anything power-wise. For the same transmitter
radiated power everybody's signals are 3 dB down (half-power) relative to
simple linear polarision when both transmitting and receiving antennas
have
the same polarisation.

The advantage of circular polarisation is that it doesn't matter which
polarisation your antenna is orientated because, in practice, when
erecting
it, the polarisation received by your antenna is usually a matter of
guesswork anyway.

Only with relatively-rare, direct line-of-sight broadcasting propagation
is
there any certainty in the polarisation of received signals.
----
Reg.

On Tue, 11 Nov 2003 11:28:30 -0500, "Tarmo Tammaru"
wrote:
As for messing up the pattern, I
would think that in the majority of cases they want equal propagation in all
directions

That would certainly account for the term "broadcasting."

However, many, many stations use directional antenna systems (speaking
of at least the AM broadcasters) that change their pattern at
sunset/sunrise.

73's
Richard Clark, KB7QHC

In message , Tarmo Tammaru
writes

"Reg Edwards" wrote in message
...
Many, if not all, FM broadcast stations in the US transmit both a
vertically
and horizontally polarized signal. So, rotating the antenna 45 degrees
is
not giving up anything.

================================

Simultaneous transmission of vertical and and horizontal polarised signals
from a single antenna system is impossible without upsetting the desired
radiation coverage pattern.

What you mean is your clever US broadcasting engineers have designed
antennas which radiate "Circularly Polarised" signals.


If you go to a broadcaster's web site, they will say X KW horizontal, and X
KW vertical, with no reference to right or left hand polarization. I take
that to mean cross polarized, rather than circular. Obviously, the reason
for the vertical component is car radios. As for messing up the pattern, I
would think that in the majority of cases they want equal propagation in all
directions

Tam/WB2TT

Transmission of vertical and horizontal, with no phase shift, produces
slant polarization. The degree of slant depends on the ratio of the
powers (ie equal powers give 45 degrees).

Transmission of vertical and horizontal, with 90 degrees phase shift,
produces elliptical polarization. Equal powers produces circular.

In the UK, most transmitters use slant or elliptical (to improve
reception for cars etc). Generally, I think that the only
horizontal-only transmissions are from a few low power 'fill-in'
transmitters. Most UK transmissions give more power to the horizontal
(so you don't see vertical domestic antennas).

Circular/elliptical is better than slant as the relationship of the
'slant' of the transmitting and receiving antennas don't matter. The
first UK transmitter to use it gave noticeably consistent signals in
difficult places (eg built-up areas).

Where slant polarization is used, I suspect that it is because it is
easier to transmit (just by slanting the antenna).

I think I'm right in saying the Irish Republic generally uses vertical
for FM (or at least used to). This obviously helps a lot for reception
in vehicles.



As Cecil says, nobody gains anything power-wise. For the same transmitter
radiated power everybody's signals are 3 dB down (half-power) relative to
simple linear polarision when both transmitting and receiving antennas
have
the same polarisation.

The advantage of circular polarisation is that it doesn't matter which
polarisation your antenna is orientated because, in practice, when
erecting
it, the polarisation received by your antenna is usually a matter of
guesswork anyway.

Only with relatively-rare, direct line-of-sight broadcasting propagation
is
there any certainty in the polarisation of received signals.
----
Reg.






Ian.
--