cooper Posted April 24, 2014 Share Posted April 24, 2014 There are *LOTS* of antenna designs for various usages. The one most popular for talking to the NOAA satellites to get the weather photos is the Quadrifilar Helicoidal Antenna. What puzzles me is that if this is perfect for talking to something as remote as a satellite (no idea of signal strength and since it's at a far lower frequency the distance can be much larger too, I get that), why don't you ever see people using these for wifi? There's an online calculator for them and the resulting antenna would be just 5cm long for 2.4 GHz and even half that for 5GHz. Sounds like you could use this type of antenna to make a really compact one, but maybe there's a reason it's apparently not used for these frequencies. So, anybody know why? Quote Link to comment Share on other sites More sharing options...
i8igmac Posted April 24, 2014 Share Posted April 24, 2014 the best results I have found is a driven biquad with a parabolic dish... like a magnified glass can focus a beam of light, a dish can focus this beam for miles... With some instructions on home built parabolic curve, you could accomplish something compact... If you do attempt a build plz share resaults and instructions Quote Link to comment Share on other sites More sharing options...
madhak Posted April 24, 2014 Share Posted April 24, 2014 (edited) The reason the quadrifilar work so well with satellite is because of the polarization, non geosynchronous satellite rotate on themselves in space, if you have a linearly polarized antenna, like ALL wifi antenna then you get 100% polarization match 1/4 of the time, and 50 % 1/2 of the time and 0% 1/4 of the time. Also this effectively mitigate multipath problem as the reflected signal reflected from a mountain will arrive out of phase but also out of polarization, so it negative effect will be lowered. To efficiently communicate with satellite, circular polarization is required, but if you listen to a wifi signal with a circularly polarized antenna then the same limitation apply as above so you wont get good signal http://sv1bsx.50webs.com/antenna-pol/polarization.html http://en.wikipedia.org/wiki/Circular_polarization Edited April 24, 2014 by madhak Quote Link to comment Share on other sites More sharing options...
cooper Posted April 24, 2014 Author Share Posted April 24, 2014 Nice. That actually makes a lot of sense. Thanks for that, Madhak. Quote Link to comment Share on other sites More sharing options...
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