Re: DIY WiFi antenna (to increase reception)

From: Unruh (unruh-spam_at_physics.ubc.ca)
Date: 06/11/05 

Date: 11 Jun 2005 16:13:26 GMT

YouCanToo <dwmoar@findmoore.net> writes:

>Floyd L. Davidson wrote:
>> Timothy Murphy <tim@birdsnest.maths.tcd.ie> wrote:
>>
>>>Stan Goodman wrote:
>>>
>>>
>>>>>>Lets look at it one part at a time, and follow the logic.
>>>>>>
>>>>>> 1) good line of sight at short distance is best
>>>>>
>>>>>This is like saying that phones are best
>>>>>if the person you are talking to is in the same room.
>>>>>True but ridiculous.
>>>>
>>>>Not so. What he is trying hard to tell you is that your best chance of
>>>>getting a good and reliable signal with a known polarization is to have a
>>>>line-of-sight between the two antennas.
>>>
>>>This might be a sensible remark if you were talking about
>>>long-range WiFi transmission, but it is a ridiculous remark
>>>if you are talking about WiFi in a house.
>>>The whole point of WiFi is that it is _not_ line-of-sight.
>>
>>
>> Multipath and polarization changes are essential to
>> understanding propagation within a building. And 2400MHz is
>> absolutely "line of sight".
>>
>he should perhaps think of the 2.4Ghz range as acting like a light beam.
>Perhaps he will get the Idea of what LOS means.

Except it is not. A light beam is stopped by a piece of paper, 2.4GHz is
not. 2.4G is stopped by aluminium screen. a light beam is not.
If you mean 2.4GHz has a tought time bending around absorbers, just as
light does, then you are right. (ie placing a square meter aluminium screen in front of
your antenna will do no good to reception, while it would do nothing to
your AM radio reception.) But that is NOT the question here. The
question he raised was the use of such receivers in the home hidden behind
walls or under floors or behind two foot thick granite walls.
 And he is perfectly correct that although such
materials present insuperable obstacles to light, they may well present
very little obstacle to 2.4GHz radio.
Thus talking about "line of sight" is silly, especially since as you have
pointed out, reflections abound in the radio whereas they do not in the
optical.

To find out if a certain material is transparent to radio waves, "line of
sight" is a useless mantra. "Try it and see" is a much better one. Of
course there are rules of thumb. Do not try it through wire mesh covered
walls-- eg do not enclose your access point in a wire cage to protect it
from the rats. But if you are in a house, try it is still the best advice,
since you almost never actually know what the microwave transparency is of
all the material in the walls/floors etc. Nor do you in general know what
their reflectivity is.

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