45 degree polarization??
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 -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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. -- |
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 |
"Sparks" wrote in message ... 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 Ok, that makes some sense then, but what's the advantage of sitting the antenna at 45 then? It should work as well at any angle, as long as it's pointed the right way. |
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Hash: SHA1 "Dave" =3D=3D Dave VanHorn writes: [... Sparks talks about storecasting ...] Dave Ok, that makes some sense then, but what's the advantage of Dave sitting the antenna at 45 then? It should work as well at any Dave angle, as long as it's pointed the right way. Sitting the antenna at 45 degrees drops the level of vertically- and horizontally-polarized noise 3db, I believe. Jack. =2D --=20 Jack Twilley jmt at twilley dot org http colon slash slash www dot twilley dot org slash tilde jmt slash =2D----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.3 (FreeBSD) iD8DBQE/sspWGPFSfAB/ezgRAsi2AJwKXbjRtz12V7ycsgUeL3a9Ibz4gwCfeoSV Omgn8k6sAY+3tf6fruNtGoc=3D =3DYwbA =2D----END PGP SIGNATURE----- |
Sitting the antenna at 45 degrees drops the level of vertically- and horizontally-polarized noise 3db, I believe. Sounds like a conservation of energy violation. Assuming noise is randomly polarized. .. I think something's still not clear here. |
Sounds like a conservation of energy violation. Assuming noise is randomly polarized. .. I think something's still not clear here. You have to be more specific, what kind of noise, source, how far. Then what it is attached to or radiated by. The "antennas" can add polarization as well as propagation. Noise can be point source, omnidirectional, omnipolarized, but also "massaged" by the surroundings and "antennas" attached to it or in vicinity. Ever chased power line noise along the power lines? Yuri, K3BU |
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Hash: SHA1 "Dave" =3D=3D Dave VanHorn writes: Jack Sitting the antenna at 45 degrees drops the level of vertically- Jack and horizontally-polarized noise 3db, I believe. Dave Sounds like a conservation of energy violation. Assuming noise Dave is randomly polarized. .. I do not share your assumption that noise is randomly polarized. The majority of noise I encounter is man-made and vertically polarized. There is a great deal of horizontally polarized noise as well. Natural noise may be randomly polarized, but that's the minority in my experience. Dave I think something's still not clear here. It makes sense to me. Jack. =2D --=20 Jack Twilley jmt at twilley dot org http colon slash slash www dot twilley dot org slash tilde jmt slash =2D----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.3 (FreeBSD) iD8DBQE/s1MLGPFSfAB/ezgRAjR/AJ4sol3z1kafeEKiJu2RGL8XZ262UACdE8WD 8WZ0OctTi61JWCfwfTeuOOg=3D =3Db4o8 =2D----END PGP SIGNATURE----- |
Well..... The origional question was "What is the 45 degree antenni
seen on mostly commercial eating places ect. That has been answered. I'm slowley recovering from a heart attack last week and will let the antenna experts stomp through the grass with the why's, where fores, and other "stuff" that can make interesting reading for a few weeks. Regards, Sparks |
"Jack Twilley" wrote in message ... Sitting the antenna at 45 degrees drops the level of vertically- and horizontally-polarized noise 3db, I believe. Jack. - -- Jack Twilley jmt at twilley dot org Jack, My original point was that if you drop the vertical and horizontal gains each by 3 db, the sum gain is still 0 db. BTW, people talk about Muzack in fast food restaurants. Never saw a fast food restaurant with Muzack. It is something else. Tam/WB2TT |
BTW, people talk about Muzack in fast food restaurants. Never saw a fast food restaurant with Muzack. It is something else. As a former Muzak installer, I can assure you, they do. I'm still skeptical on the idea that most noise is either vertical or horizontal, and that rotating an antenna 45 deg will cut both by 3dB Also, this would be an FM service, where such noise would normally be insignificant. |
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