Keith Hughes wrote in
:

Well, I'm sending this on an ATT/Cincular aircard right now,
from S.
San Francisco, not 4 miles from the airport. I'd *kill* for
500Kbps
on a regular basis! On a "regular" basis, here on the job
site,
50-60Kbps is a good day - interspersed with PPP errors and
service
dropouts. My buddy here on the same site is with Verizon, and
he
get's "better" service, but not by much.

Sitting on my boat, across the jetty from the San Diego
airport, I can
get maybe 150Kbps on average - - interspersed with PPP errors
and
service dropouts. From my boat, my buddies' Verizon card is
solid,
and smokes the Cingular card for transfer rates. I'll go
Verizon next
time...

Keith Hughes



A lot of what you're seeing, I'm sure, is caused by "multipath"
causing terrible data errors. Look at any UHF TV running on the
little loop that comes with the TV. See all those "ghosts" we've
seen all our lives on analog TV? That's multipath.

The analog TV scans from top to bottom, left to right, just like
English reads. The horizontal scanning is very fast, indeed, at
about 15,000 lines per second. There is a finite distance in
time being measured as it scans, linearly we hope so it doesn't
distort the picture. The signal that hits the TV first is the
main signal direct from the TV station to you, via the shortest
path, not bouncing off anything. Then, to the right of that
picture, some distance in time AFTER the main signal comes in
direct, is more than one "ghost" pictures, that arrive over a
longer path, later than the main signal. The ghosts are always
to the right as time on the display passes to the right.

ANY RF device, no matter how much wishful thinking and slick
marketing goes on, is subject to this multipath physics. Any
reflective object that bounces RF causes a multipath signal to
arrive late. You can imagine what this does to the very high
speeds being demanded of the broadband uses of UHF cellular
systems. These systems have error correcting schemes built into
the various genres to correct data errors caused by multipath,
noise, etc., but correcting errors TAKES TIME. Taking time is
reflected (no pun intended) in every lowering throughput...lower
data rates...as conditions on the air worsen.

What can you do? Numero Uno is just what the TV viewer
does...PUT UP AN ANTENNA! A directional antenna array such as a
yagi beam, corner reflector, panel antenna like the cell company
uses, that points the ears of your system towards the intended
target reduces the effects of multipath, increases the strength
of the desired signal over the noise level and throughput
increases because less error correction is going on. On TV, it
reduces, or completely eliminates the "ghosts". (On your new
ATSC digital TV, you won't see ghosts. Multipath and noise
simply result in NO DATA and NO PICTURE. You are NOT going to be
watching ATSC digital TV from a MOVING vehicle. That's not going
to happen and I think portable TVs will become a relic.

You could, I suppose, MOVE to FLAT country....(c;



Larry
--
You can tell there's extremely
intelligent life in the universe
because they have never called Earth.