> hpeyerl@beer.org (Herb Peyerl) writes:
> > I wonder how far I can get with this 24.5dB gain antenna here...
> 
> I've seen urls where folks set up 10-20 mile 802.11b links.  The
> biggest catch seems to be that the antennas and lead-in cables are
> still priced like industrial items.

It is even worse than that.  Coax is lossy at 2.5 GHz, so you pay
a lot for the cable since it is high tech and hard to make.  100'
of LMR-400, which is almost half an inch in diameter, kind of stiff
and probably approaching $1.00 per foot, still loses about 7 dB, plus
maybe 3 dB for the connectors, so your 20 dBm card's output ends up being
10 dBm at the antenna, with a similar loss on the receive side (cheaper
stuff like RG-58 is a disaster).  To fix this what is usually needed is to
keep the card very close to the antenna, which sucks since you want
the antenna outside and as high as possible, or failing that to put a
bi-directional amplifier on the pole very close to the antenna, so the
transmit power is bumped back up at the antenna and the received signal
is amplified prior to the cable losses.  If you decide to go the
amplifier route, however, FCC Part 15 demands that you buy the antenna,
amplifier and pigtail for the card in one certified kit since the
rules for legal output power are arcane (you are allowed 1 W
output power if the antenna is less than 6 dBi gain, but only 250 mW
for the 24 dBi grid/dish mentined above) and they want to make sure
you don't mix-and-match things that don't go together.  This means you
can't shop around for components, which makes the price higher still.
I've used stuff from

    http://www.hyperlinktech.com

but the whole thing is unpleasant enough that it is no surprise that
this isn't popular.

> If some of the San Francisco Bay area folks want to try setting up a
> link, I might be game.  I've got a clear shot to much of the south bay
> from my roof.  (I can also dig some other URL's if there is a general
> interest in this sort of thing.  With high-speed ISP's closing shop
> and filing chapter 11 on a daily basis around here it might be nice to
> have a fall-back connection.)

If you can see as far north as Palo Alto I might be willing to play, if
I can get my equipment back from the kid I lent it to on the street the
old house was on (he had an 18 dBi antenna pointed at something, which
with my 1 W amplifier probably means he has mixed-and-matched things
which don't belong together...).

> > So according to their website, there's yet another reason not to buy the 
> > linksys cards.  only 14dBm or <50mW.   (in addition to NetBSD not being able
> > to use WEP on the linksys cards).
> 
> Yup, to be exact thats only 25 mW.

Yes, unless it is the battery life in a laptop one is trying to optimize.
In that case you might want to look at the typical power consumption of
the card as well, since even with power control the lower-power cards
sometimes (though not always) draw less current from the PC under the
same conditions.

Dennis Ferguson