On Sat, 16 Jul 2005 15:16:22 -0400, <riggor9999> wrote:

>I have setup a 802.11b wireless bridge between two buildings - use the first
>generation Linksys WAP11 access points (the ones with the USB port).

I have about 5 of those pieces of junk in a pile somewhere. They were
the first cheap transparent bridge radios in their day. After about 5
major revisions of the Atmel firmware, and the pieces of junk were
still locking up all the time, I gave up on them. I'm glad you got
them working.

Incidentally 1.0 and 1.1 had the USB port. 2.2, 2.6 and 2.8 did not
have the USB port. 1.0 was junk. 1.1 is improved junk that didn't
lockup as much. 2.2 and above are fine.

>- I used the hack and boosted the signal to 100% on each.

Good for you. I wonder if the FCC offers a reward for turning in
spectrum polluters? The problem is that cranking up the power beyond
the rated and tested levels causes the tx amplifier to spray garbage
beyond the typical 26MHz of occupied bandwidth for 802.11b. It also
creates amplitude (envelope) distortion which severely affects the
ability of the receiver to extract the data. You may crank out more
RF, but how much of it is in the receiver bandpass, and how much of it
can be used by the receiver is questionable.

As I recall, the WAP11 running DWL-900AP+ firmware, which is what I
guess you were doing, doesn't really increase the tx power enough to
cause a problem. However, if you find that you are running a system
sufficiently marginal that you need the extra power, methinks you
should look instead for a better antenna pair or better line of sight,
as such a marginal system is sure to eventually fail when something
changes.

>- The one unit is sitting in a basement window. The antenna's were replaced
>with the radio shack 6db "duck" ones.
>- The other unit is sitting below a window on a shelf, and I put a single
>Hawking "high gain 6db" on it ...because it had a 2 ft cable - allowing me
>to put it antenna on the sill.
>- The two have clear line of site and are about 75' apart

Are the at the same vertical elevation? If not, the omni antennas
should be parallel to each other for best performance. I would NOT
use omni antennas for such a point to point link. The WAP11's have
RP-TNC connectors and decent antennas are easy to build or buy. My
version of the common biquad in an outdoor box:
http://802.11junk.com/jeffl/pics/antennas/biquad2/

>Everything worked great for 2 years. Now the interesting part......
>
>The one building had the windows replaced with new Andersen windows. That's
>the window with the 10" high Hawking H-AI6SIP antenna
>(http://www.amazon.com/exec/obidos/AS...160163-9816714)

6dBi of antenna gain (maybe) with about 3ft of RG-316 for a loss of
1dB. Net gain is about 5dBi if you ignore connector and adapter
losses.

>. The bridge now would no longer work. When the window was open - it
>worked. When the window was closed, it would not. FYI - the original
>window was a standard wood frame, single pane of glass, not metal or
>plastic - all wood window.

It's difficult to tell without seeing the window. Many windows have a
sputtered aluminium coating to improve insulation qualities. Most
double pane windows do this. Blocks RF quite nicely. The new science
building at the local university (UCSC) has windows almost impervious
to RF which is causing problems using cell phones inside the building.

Another possiblity is a vertical difference in elevation as I
previously asked. The Hawking antenna tend to radiate most of its RF
near the base of the antenna. If the base was partially obstructed by
a metal frame window, then you will have some signal loss. Similarly,
the wooden frame window will pass more RF throught the wooden frame.

>I was going to look at getting an outside antenna and run a wire into the
>house, etc .... but I had a spare Belkin F5D6900 antenna
>(http://www.amazon.com/exec/obidos/tg...&s=electronics)
>that is supposed to be used with a PCI desktop card. It is much shorter -
>about 3 inches high and just clears the bottom part of the window frame.
>The Belkin antenna is not a "high gain" antenna.

I'm not sure I would even call it an antenna. Zero specifications on
the Belkin web pile. No clue as to the gain, length of cable, or type
of cable. My guess is a simple vertical coaxial antenna with a
theoretical gain of 2dBi, perhaps 3ft of cheap non-PTFE coax for a
loss of about 1.6dB, with a net gain of 0.4dBi. Don't bother.

What part of the antenna "just clears" the window frame? This is
critical as the entire antenna, including parts of the base, must
clear the window frame. If not, and you get too close to the metal
frame, you end up detuneing the antenna, creating VSWR, havoc, etc.

>Once I swapped the Hawking with the Belkin - the connection re-established
>and all is well - when the window is open and closed.

Well, I'm suprised as I would think the Hawking antenna would have
more gain than the Belkin. Elevation difference (tilt angle) again?

>Anyone have any ideas on why it ..
>1) the Andersen window blocked the signal, and

Metal frame instead of wood. Aluminium sputtered coating.

>2) why the Belkin antenna worked when the Hawking would not?

Dunno. Many such antennas have a tendency to place much of their RF
in the upwards direction. Uptilt is more of a problem with high gain
omni antennas, where you could easily send the signal over everyone's
heads or to the sky instead of the ground. However, on all counts, I
would have expected the Belkin antenna to be far worse than the
Hawking. Assuming everything is working properly, I'm guessing that
you have a really marginal link, where any small changes in position
or antenna location will cause difficult to predict changes in antenna
patterns. For example, reflections from the window frames or other
objects in the path. Is your system *VERY* sensitive to exact antenna
location?

However, you're doing this all wrong. Omni antennas are not a good
idea for a point to point link. Use directional gain antennas. Even
two coffee can antennas would be a major improvement. Coffee can
antennas are about 8dBi gain. Single panel antennas are about the
same. Biquad's can go up to 10dBi gain. Assuming your existing pair
of omnis each has a gain of 2dBi, a pair of biquads will yield a 16dBi
increase in fade margin, which is a *HUGE* improvement. Maybe then
you might turn down the RF power to normal levels and not trash the
neighborhood.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558