[TriLUG] Wifi Bridge

[Joseph Mack NA3T via TriLUG]

On Wed, 28 Oct 2015, Bill Farrow via TriLUG wrote:

> An RF solution. I love it. 2.4GHz Wifi has a wavelength of 12.5cm
> (4.92 inches for those stuck with olde-world measurements). Cut
> rectangular slots or circular holes ? (This is probably not going to
> allowed, but it is a fun thought process).

Rectangular slots.

Do a dry run. Buy a 8'x4' sheet of hard blue foam insulation 1/2-3/4" thick from 
Lowes etc. It has paper glued on one side and Al foil glued on the other. For 
our purposes you can assume that the foam/paper is not there; it's just a sheet 
of self supporting Al foil.

If you have vertical slots, you'll have horizontal polarization. Cut slots like 
this, with a razor blade peeling off the Al foil. These measurements are taken 
from a slotted waveguide antenna for 2.4GHz wifi sitting in my living room. The 
slots are shorter than 6.25cm because of end effects that I don't know how to 
calculate.


        I  ^
        I  |
1,8cm->I
        I
        I

          16.5cm 
I
I
I 6.0 x 0.7cm
I
I
           |
           v
        I
        I
        I
        I
        I


I
I
I
I
I


Eash slot (the column of 5 "I"s is 6.0cm*0.7cm) with round ends (the 6.0cm is 
measured to the outer edge of the round ends, not to the center of the round 
ends). There are two columns of slots with repeating distance of 16.5cm. The two 
columns are separated horizontally by 1.8cm. I suggest you start with four slots 
as above. If you mess up, tape some Al foil over the disaster and start again.

When you have your four slots stand the board up in the yard facing the free 
wifi. If you do it outside, you won't be receiving reflections from inside the 
house. Cover the slots with kitchen Al foil and go around the back of the board 
with netstumbler (or your favourite signal strength meter).  Hopefully you in an 
RF shadow. Then take off the Al foil and you should see the signal coming 
through the slots. Since the slots are 4 high and 1 across, the output should be 
a slight horizontal fan.

If that works. Open the door to your shed and put the board there. If you have 
signal inside the shed now, all you have to do is cut out a piece of your board 
say 30*6cm and stick it in your wall.

Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) austintek (dot) com - azimuthal equidistant
map generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!