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#1
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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. 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. |
#2
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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! =----- |
#3
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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. |
#4
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"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. |
#5
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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 |
#6
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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. -- |
#7
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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? |
#8
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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 |
#9
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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 |
#10
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Reg wrote:
"Isn`t Yagi a Japanese name?" Uda though so! Best regards, Richard Harrison, KB5WZI |