On Wed, 18 Dec 2013 05:10:15 +0000, Danny D'Amico wrote:
NOTE: The narrow beamwidth is how the antenna gets all that gain in the
first place.
I didn't explain that one all too well.
Here's another try at my thought process:
1. If I put the legal limit of 4 Watts into an antenna with a wide
radiation pattern, it goes only so far.
2. If I then change the antenna pattern to be more narrow, the
radiated signal goes farther in the direction that it is pointed.
So, my antenna & dish reflector, having a gain of 24dBi, is pretty
narrow at around 5° beamwidth (in both horizontal & vertical planes).
Breaking out my trig (SOH, CAH, TOA), I see that I can create a right
triangle of half the 5° beamwidth, with the Adjacent being 3 miles.
Since I have the angle and the Adjacent, and I want the Opposite,
it looks like the tangent will tell me the how large of a circle is
painted on the WISP antenna 3 miles away.
1. TOA means Tangent is equal to the Opposite over the Adjacent.
2. So the Adjacent times the tangent is the Opposite.
3. 3 miles time the tangent of 2.5° is what I need to know.
4. Googling for "tangent calculator", again I take the first hit.
5. That's
http://www.rapidtables.com/calc/math/Tan_Calculator.htm .
6. The tangent of 2.5° = 0.04366094 .
7. So 3 miles x 0.04 is about 633 feet.
8. The 2.5° was half the beamwidth (to make a right triangle).
9. So the beam paints a pattern twice that, at about 1200 feet.
10. This tells me that a beamwidth of 5° isn't really all that narrow!
Note: The 5° is defined, I think, by where the furthest lobe's power
is cut in half (i.e., by 3dB).
Here is a picture of that pattern from the Rocketdish RD-2G-24:
http://farm3.staticflickr.com/2890/1...854acbb9_o.png
Notice that this radio is pretty directional, but even so, I have
a catcher's mitt about 1200 feet wide to hit my access point.
Here are the Internet speeds I get by hitting that catcher's mitt:
http://farm4.staticflickr.com/3743/1...187217bd_o.png
All I'm trying to do is *improve* on those Internet speeds, by
understanding first, and then lowering my noise (or raising my
signal-to-noise levels) within legal limits of 36 decibels EIRP.
REFERENCE:
http://dl.ubnt.com/datasheets/rocketdish/rd_ds_web.pdf