Concur with Tim's experience and the issues with doing this.
Additionally, Sprint Broadband Wireless engineers told me they have similar difficulties trans-Bay from San Bruno (near Sign Hill) to Berkeley, Oakland, etc. - visual line-of-site but several 'environmental' factors involved - Bay Bridge, the Bay (waves are highly variable reflectors), the distance and the marine layer.
Get two hams, two sets of 2.4 GHz gear with signal strength indications, coordinate antenna alignment live. What we need is a good 100-500mW CW beacon transmitter and a complimentary receiver with signal strength and Sinad readouts as a test set...hmmmm....
SF-Berkeley is the toughest shot, over water with the Bay Bridge clutter, etc. - the rest would be easier from hilltop levels, but from ground or even building top level - ooooooohhhh - tough call.
Stretching a 300 meter technology at these power level out to 10-30 km is asking a bit much no matter which antenna, etc. you're using.
At 12:00 PM 12/11/2002, you wrote:
1. Re: Cross-Bay link (Tim Pozar)
Message: 1
Date: Tue, 10 Dec 2002 11:59:57 -0800
From: Tim Pozar <[EMAIL PROTECTED]>
To: "Robert R. Ballecer, SJ" <[EMAIL PROTECTED]>
Cc: [EMAIL PROTECTED]
Subject: Re: [BAWUG] Cross-Bay link
On Sat, Dec 07, 2002 at 06:30:56PM -0800, Robert R. Ballecer, SJ wrote:
> Has anybody had experience with shooting 802.11b across the bay? I ask
> because my organization has properties Fremont, Berkeley, San Jose, Santa
> Clara (University), Los Gatos, Los Altos and San Francisco. Each location
> is high enough to be able to "see" at least two of the other sites through a
> telescope. There are not many practical uses for the link at the moment
> (each site already has broadband access) but it might be a nice project for
> my free time.
>
> I was thinking about getting a few of those Senao 200mw cards and use them
> in conjunction with some homebrew antennas. Anybody have the equations I
> need to figure out how the distance will affect S/N? What says the FCC about
> 200mw cards?
We tried one 20 mile link with 250mW amplifiers from Sign Hill in
South San Francisco to a house in Hayward. The antennas were 24dBi
dishes. We were able to get both ends to associate and get some
data back and forth, but not consistently. You can see the path
profile at:
http://www.lns.com/projects/sunsetwireless/paths/Matt2SignHill.pdf
Some of the problems we ran into was antenna alignment. 802.11
radios do not update C/N data fast enough and the data tends to
bounce around. We decided that in order to line up paths you really
need to use different transmission gear for antenna alignment such
as a carrier wave at the frequency you want and a spectrum analyzer.
This also helps as you really have a hard time tracking SS signals
on a spectrum analyzer.
Of course there are a number of things you need to look at before
you get to this point. Looking through a telescope will pass some
some tests but you need to look at other things like "refraction"
and "fresnel zones" to insure that the data will get from one
transmitter to the other. I think there has been some discussion
on the list before in "engineering" paths. If not, I can put
together one.
Tim
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