Dipole? antenna
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From: Tim Wescott on 8 Aug 2006 14:23 Richard Owlett wrote: > I deliver blood to hospitals. > In one hospital I see a "structure" which I would describe as 2 dipoles > in common (horizontal) pale at 90 degrees. > > Because the are in certain corridors but not others I assume them to be > part of an INTERNAL communication system. > > Two questions. > > 1. If indeed two dipoles at right angles, what would the field be? > 2. What am I looking at? > At a guess it's a turnstile antenna, for an omnidirectional pattern with horizontal polarization: http://www.cebik.com/wire/turns.html -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
From: Richard Owlett on 8 Aug 2006 16:29 Tim Wescott wrote: > Richard Owlett wrote: > >> I deliver blood to hospitals. >> In one hospital I see a "structure" which I would describe as 2 >> dipoles in common (horizontal) pale at 90 degrees. >> >> Because the are in certain corridors but not others I assume them to >> be part of an INTERNAL communication system. >> >> Two questions. >> >> 1. If indeed two dipoles at right angles, what would the field be? >> 2. What am I looking at? >> > At a guess it's a turnstile antenna, for an omnidirectional pattern with > horizontal polarization: http://www.cebik.com/wire/turns.html > Looked at page. Seems to match. Thanks
From: Joerg on 10 Aug 2006 20:59 Hello Richard, >>> I deliver blood to hospitals. >>> In one hospital I see a "structure" which I would describe as 2 >>> dipoles in common (horizontal) pale at 90 degrees. >>> >>> Because the are in certain corridors but not others I assume them to >>> be part of an INTERNAL communication system. >>> >>> Two questions. >>> >>> 1. If indeed two dipoles at right angles, what would the field be? >>> 2. What am I looking at? >>> >> At a guess it's a turnstile antenna, for an omnidirectional pattern >> with horizontal polarization: http://www.cebik.com/wire/turns.html >> > If you travel to Europe look at the roofs of older houses. They have those for (near) omnidirectional FM reception. > Looked at page. Seems to match. > Thanks > If they were in a pail on its side the purpose is different: This way they want to make sure that horizontal and vertical polarizations are both covered. If you hold a radio with its stub antenna up it'll prefer vertical polarization but if you slip it into a coat pocket and it lands on its side it will be mostly horizontal. For the same reason many WLAN routers have two or more antennas that are supposed to be oriented at an angle, not both of them straight up. -- Regards, Joerg http://www.analogconsultants.com
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