Wifi Past Buildings

Discussion in 'Wireless & RF Design' started by mokhd, Nov 13, 2012.

  1. mokhd

    Thread Starter New Member

    Nov 9, 2012
    i thought of asking if anyone tried this idea before as i want to get a wifi signal past by a building[​IMG]
  2. wmodavis

    Distinguished Member

    Oct 23, 2010
    "building with reflective glass panes"

    Reflective to light or to 2.4GHz radio waves or reflective to light?
  3. mokhd

    Thread Starter New Member

    Nov 9, 2012
    just regular glass panes that usually reflect light
  4. vk6zgo

    Active Member

    Jul 21, 2012
    At 2.4GHz,any building will be reflective.
    Seems like a good idea,but you will need proper directive antennas.
  5. mokhd

    Thread Starter New Member

    Nov 9, 2012
    so i guess this will work ,yes??
  6. bertus


    Apr 5, 2008
  7. WBahn


    Mar 31, 2012
    Depending on the coatings on the windows, you signal may largely go through, may reflect, or may get absorbed.

    But you also have to be concerned about the multipath situation you are inviting.

    At 2.4GHz your carrier wavelength is about 12.5cm.

    Let's say that the horizontal distance (in the drawing) between the antennas and the reflective buildings is 200m and that the two antennas are separated (vertically in the drawing) by 500m. Let's now say that the building you are reflecting off of is 50m wide and one end of the building is located midway between the two antennas.

    The total path length when bouncing off this corner will be:

    D1 = 2*sqrt[(250m)^2+(200m)^2] = 640.3m

    The total path length when bouncing off the other corner will be:

    D2 = sqrt[(200m)^2+(200m)^2] + sqrt[(300m)^2+(200m)^2] = 643.4m

    D2-D1 = ~3m = 300cm = ~24 wavelengths

    You may have even longer distances vertically (and keep in mind that I'm just guessing at ballpark dimensions here).

    This means that you can experience significant multipath fading and interference. The time difference is going to be ~10ns. This could result in noticeable intersymbol interference, as well, depending on the baud rate.
  8. JMW

    Active Member

    Nov 21, 2011
    This is interesting, let us know how it works. I would recommend an antenna with circular polarization to minimize multi-path fading. Keep in mind the polarization will flip from RH to LH (or vice versa) as it bounces off the building. The only problem I see is if the people in the "reflector" building cause a fuss. Remember the silliness caused by 60 Hz electromagnetic waves from CRT monitors and fluorescent lamps. Well the same thing is happening with RF. I just read where a FL city has passed an ordinance requiring cell phones to have a warning sticker attached. This is the 2nd or 3rd city that has done this. I guess you could tell the folks in the building, you have discovered their building is generating dangerous levels of Bill Shutsky rays, and you are only neutralizing them.