Circular polarization is used to prevent "picket fencing" - the signal dropping out repeatedly as one moves through areas where reflections meet to create a null in the signal. And you pay a price for that because the receive antennas are not circularly polarized. So there's a polarization mismatch.
Greg On Apr 5, 2010, at 1:09 PM, Mike wrote: > Have you ever taken a really good look at an FM broadcast antenna? Most are > circularly polarized so they can be received by both horizontal and vertical > receive antennas. Even at 90 MHz they aren't that large either. My choice > of sector would be something like that, and would be made of aluminum parts, > not panels like we are used to using now. I predict circular polarity will > be the norm. Why? Because theoretically, a receive antenna of opposite > circular sense exhibits infinite loss. My experiments have shown that > reality is less, but you CAN expect at least 30 to 40 dB of isolation. The > same 6 MHz segment could be reused on the same tower. The phasing harness > on the CPE antenna would have to set to either left hand or right hand > circular polarization. > > Friendly Regards, > > Mike > > Mike Gilchrist > Disruptive Technologist > Advanced Wireless Express > P.O. Box 255 > Toledo, IA 52342 > 239.770.6203 > [email protected] > > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Mike Hammett > Sent: Monday, April 05, 2010 12:23 PM > To: WISPA General List > Subject: Re: [WISPA] WISPA TV Whitespaces Meeting with the FCC > > Then the problem arises of frequency reuse if we have such low gain antenna > all over the place... and the size of a sector antenna for towers. > > > ----- > Mike Hammett > Intelligent Computing Solutions > http://www.ics-il.com > > > > -------------------------------------------------- > From: "Mike" <[email protected]> > Sent: Monday, April 05, 2010 11:59 AM > To: "'WISPA General List'" <[email protected]> > Subject: Re: [WISPA] WISPA TV Whitespaces Meeting with the FCC > >> Just for discussion, let's say a TV LPDA has a gain of 8 dBi. It will >> cover >> the entire VHF TV band, and by superimposing a UHF LPDA on the same mast, >> can cover the entire UHF TV band with similar gain figures. >> >> I'd make this challenge: >> >> I could TRY to hide a TV band LPDA on my property and beg you to find it. >> Even well hidden, you would. Now, give me a few hours to build a narrow >> band antenna with similar gain in ANY 6 MHz segment of the same bands, and >> let me try to hide it. Do you think I could hide it well enough you >> wouldn't find it? I know I can. >> >> My point is, the antenna which will be needed for any segment of the >> whitespace will be much less intrusive than the LPDA (or Yagi) being used >> for comparison. >> >> This is great dialogue. I hope we are faced with the challenge of >> deploying >> in these bands. >> >> Mike >> >> >> >> >> > ---------------------------------------------------------------------------- > ---- >> WISPA Wants You! Join today! >> http://signup.wispa.org/ >> > ---------------------------------------------------------------------------- > ---- >> >> WISPA Wireless List: [email protected] >> >> Subscribe/Unsubscribe: >> http://lists.wispa.org/mailman/listinfo/wireless >> >> Archives: http://lists.wispa.org/pipermail/wireless/ >> > > > ---------------------------------------------------------------------------- > ---- > WISPA Wants You! Join today! > http://signup.wispa.org/ > ---------------------------------------------------------------------------- > ---- > > WISPA Wireless List: [email protected] > > Subscribe/Unsubscribe: > http://lists.wispa.org/mailman/listinfo/wireless > > Archives: http://lists.wispa.org/pipermail/wireless/ > > > > > > -------------------------------------------------------------------------------- > WISPA Wants You! Join today! > http://signup.wispa.org/ > -------------------------------------------------------------------------------- > > WISPA Wireless List: [email protected] > > Subscribe/Unsubscribe: > http://lists.wispa.org/mailman/listinfo/wireless > > Archives: http://lists.wispa.org/pipermail/wireless/ -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: [email protected] Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
