[115369] in North American Network Operators' Group
RE: Wireless bridge
daemon@ATHENA.MIT.EDU (Tim Huffman)
Thu Jun 18 12:28:21 2009
From: Tim Huffman <Tim@bobbroadband.com>
To: "nanog@nanog.org" <nanog@nanog.org>
Date: Thu, 18 Jun 2009 11:27:28 -0500
In-Reply-To: <09ef01c9f02d$221f21f0$665d65d0$@com>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
> The line of sight is all clear, no trees. Only one building along the way
> has a rooftop of similar height, but the antennas are extended far above
> the
> roofline. We have used a rifle scope to confirm line of sight is all clea=
r
> at all angles.
>=20
Unfortunately, you can't necessarily rely on visual line of sight. At 800me=
ters, the Fresnel Zone on your radio is about 14ft in diameter at the midpo=
int. You need to make sure that this is free of obstructions.
> Oh I know. Luckily it's located in an industrial area just on the
> outskirts
> of the city. There isn't a lot of other WiFi (in my opinion); 3-5 total
> SSIDs spread across 2 of the 3 physical channels (1,6,11) depending on
> which
> rooftop you measure from.
>=20
Make sure you're using the channel that doesn't have an AP on it!
>=20
> Bandwidth requirements aren't too picky. If it can handle minimum 9 Mbps
> full-duplex everyone will be happy. Of course, the faster the better.
> I don't know if it makes a difference or not but this is all taking place
> in
> Canada. I don't know of any regulations drastically different from the
> U.S's
> regarding frequency use here. The biggest problem I've ever had though ha=
s
> just been payment/shipping depending on the supplier (some don't ship to
> Canada or are very specific about payment methods!).
Canadian and US regulations are very similar in the unlicensed bands. I'd s=
till pick 5.2GHz if you were replacing the radio.=20
>=20
>=20
> Just to answer a few more questions I've been getting, the access points
> are
> located inside, connected to a small UPS. The antenna wire is a very thic=
k
> coax up to the roof, BNC connectors to the access point and I'm fairly
> certain BNC connectors on the antenna end as well. I'll double check
> grounding on the poles but I'm somewhat afraid to turn it into a lightnin=
g
> rod. I'm fairly certain that the ground in the antenna wire is clean but
> again, something to double check.
How long is your cable run, and what kind of cable is it? It's probably LMR=
-400 (the most common) loses about 6.6dB of your signal for every 100 feet.=
Also, you should check the waterproofing on the connector at the antenna. =
We normally use a 'courtesy wrap' of electrical tape, followed by a thick l=
ayer of Mastic tape, followed by another layer of electrical tape. Also, ch=
eck your cable for nicks or kinks.
>=20
> Rain/moisture doesn't seem to cause problems. In fact the connection is
> more
> reliable through the winter. The last 2 months here have been cold/warm,
> dry/wet and there's been no pattern to the stability issues. The only
> correlation between weather and stability that they have noticed there is
> lightning related.
Moisture in the cables doesn't necessarily show up during rain! That moistu=
re can seep throughout the cable, and cause attenuation when it gets cool a=
nd the moisture condenses, for example.
You haven't said what kind of antennas you are using, but if they are yagi'=
s, they probably have very poor back-to-front ratios, which means that you =
could be picking up interference from behind you, or on the sides, especial=
ly if the antennas are up above the tree cover. You might try horizontal po=
larization on the antennas (just rotate them 90 degrees, but make sure you =
do it on BOTH sides!) to see if that helps. Cross-polarization is usually g=
ood for about 20dB of noise rejection.
The fact that there doesn't seem to be any pattern to your loss means that =
it's probably either interference (somebody changing channels), hardware fa=
ilure, or software failure.
Hope this helps.
--
Tim Huffman
Director of Engineering
Business Only Broadband, LLC
O (630) 590-6012
C (630) 340-1925
tim@bobbroadband.com
www.bobbroadband.com
