And so you see, all this clever radio engineering on both sides of the
Atlantic has come about to just to cover up the disorientated shortcomings
of TV and FM antenna installers, and inadequate tightening of fixing bolts.
;o)

Isn't Yagi a Japanese name?

I've seen this also, and wondered about it.
Dipoles, or 3 element yagis usually, mounted at 45 degree polarization, on
commercial buildings.

I did some wierd things in my MATV days.. YOU try getting a nice clean
signal in downtown Honolulu..

Please see comments below...
___________________

"Reg Edwards" wrote (in part):

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

Sorry, but that statement is incorrect as it applies to FM broadcasting, at
least. There are many commercial FM broadcast transmit antenna designs
capable of doing so, for example the cavity-backed radiator (CBR) introduced
by Harris Corporation in the U.S, and used for simultaneous transmission of
8-10 FM channels in r.h. circular polarization at 100kW ERP each. Examples
are the Senior Road Tower Group in Houston, and Master FM sites in Miami and
St Louis.

The CBR is a panel type antenna designed to mount on and around the faces of
a tower, and has azimuth pattern circularity and axial ratio of less than
~1.5dB on a tower of ~2 meter face width. Other OEMs such as Kathrein,
SIRA, ERI, Dielectric etc supply other designs nearly as good.

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.

Incorrect again, at least in the US, where FM broadcast ERP is defined only
for horizontally polarized radiation. Therefore the output power of the
transmitter itself is raised 3dB so that the station's full, authorized ERP
is produced in all radiation planes. In theory, a r.h. CP receiving antenna
actually will receive 3dB MORE signal from CP transmission than when linear
polarization is used. For CP transmit and linear receive, received field
strength would be the same as if the transmit antenna also was linear, with
the same ERP in the same plane.

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-sigh
it broadcasting propagation is there any certainty in the polarisation
of received signals.

The full benefit of CP transmission is realized only when a CP receive
antenna is used. A CP receive antenna will tend to reject reflections of
the transmitted signal (multipath), because the physics of producing the
reflection causes a reversal of its polarization sense -- which the CP
receive antenna will reject. Reduced multipath content makes for "cleaner"
reception. Not too practical in automobiles, though, where it is most
needed.

RF (retired broadcast engineer - RCA and Harris Corp)

Visit http://rfry.org for FM broadcast RF system papers.

On Wed, 12 Nov 2003 01:08:13 +0000 (UTC), "Reg Edwards"
wrote:

Isn't Yagi a Japanese name?

Japanese-Italian. Antennio Yagimoto.

gm
--
Replace x in adr with c

Reg wrote:
"Isn`t Yagi a Japanese name?"

Uda though so!

Best regards, Richard Harrison, KB5WZI

On Mon, 10 Nov 2003 23:08:49 +0000 (UTC), "Reg Edwards"
wrote:



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.

Reg-

In the mobile radio world, where you do not generally have line of
sight propagation the polarization is best described as random, as it
arrives via multiple paths that change as the user moves or the
surroundings change. Hence, there is no preferred polarization
orientation for the mobile handset.

In fact, you'll find polarization diversity receiving antennas at base
stations, with either switched receivers or maximal ratio combining,
using two receivers, one fed with a vertically polarized antenna and
one with a co-located horizontally polarized antenna. Usually this
works pretty well, just a bit inferior to space diversity, but it's
quite a bit cheaper for the operator, as the V and H antennas can be
put into the same radome, thereby saving antenna rental space.

And, yes, I know polarization diversity goes way back in history and
has been used in HF diversity reception, but it has come back into
widespread use in cellular and PCS base stations.

Jack K8ZOA

mcduffie wrote:
"Japanese-Italian. Antonio Yagimoto."

Kraus wrote:
"Hidetsugu Yagi, professor of electrical engineering at Tohoku
University and 10 years Uda`s senior, presented a paper with Uda at the
Imperial Academy on "Projector of Sharpest Beam of Electric Waves" in
1926, and in the same year they both presented a paper before the Third
Pan-Pacific Congress in Tokyo titled "On the Feasibility of Power
Transmission by Electric Waves."

Best regards, Richard Harrison, KB5WZI

Reg Edwards wrote:
In some cases the fixing nuts and bolts have come loose.


So ... with regards to my original question, one respondant voted that
those slant-polarized antennas are for reception of 'storecasting'
music, one felt it was just an attempt to cover both vertical and
horizontally-polarized sources, and one who thinks it's just loose
nuts. (and a whole lot of topic-drift discussion about the type of
polarization used in broadcast stations).

With regard to Reg's nuts-n-bolts suggestion, I've seen these antennas
far too often and in far too exact a 45 degree state for them to be
simply loose hardware.

So - other suggestions? Any support for the 'storecasting' idea? One
place I saw one of these was on a MacDonalds, another was a bank, so
Muzak would make sense. Still, why would so many be off-polarized?
Clueless installers covering both bases when they don't know the
'real' polarization? Some special service that transmits at that odd
angle?

Bob, KI8AB

With regard to Reg's nuts-n-bolts suggestion, I've seen these antennas
far too often and in far too exact a 45 degree state for them to be
simply loose hardware.

The ones I've seen didn't look accidental either.

So - other suggestions? Any support for the 'storecasting' idea? One
place I saw one of these was on a MacDonalds, another was a bank, so
Muzak would make sense. Still, why would so many be off-polarized?

Muzak or similar services may do their own transmitters in some places, they
frequently operate on subcarriers on the local FM stations.

I've seen them on fast food places as well.

Plot by space aliens to kill us all with junk food?

Clueless installers covering both bases when they don't know the
'real' polarization? Some special service that transmits at that odd
angle?

Poissible, but it takes some effort to get to 45 degrees, most antenna booms
are pre-drilled for 0 or 90.

It IS STORECASTING in ALL instances in Florida. It is 45 degrees.
You-All are missing the true fact in the USA, "Most" stations use dual
polorized antenni and a very large number use circular. Broadcast
Consultant