Rick,
My comments were directed at omni-directional antenna deployment.
Directional antennas are different in that their radiation footprint is
focused. The 3 foot rule is not a bad starting point, but take a close
look at the published antenna gain chart for the particular antenna.
Some directional antennas have pretty substantial side and rear lobes in
their radiation pattern. I remember doing some point-to-point links
where we had to stagger the antennas on a tower by up to 6' to prevent
side and rear lobe interference. I've also done sector antennas that
were very close together (8"-18") without incident.
If anyone remembers the issues with early Vivato panels, they put out a
technical bulletin suggesting that only channels 1 & 11 be used because
of the adjacent channel interference. While beam-forming is way cool,
it is also subject to adjacent channel interference, just like regular
APs and antennas.
My best advice is to get <some> separation for your co-located
directional antennas, but you may be able to get by with less than the 3
foot rule of thumb. Of course, YMMV...
>>-> Stan Brooks - CWNA/CWSP
Emory University
Network Communications Division
404.727.0226
[EMAIL PROTECTED]
AIM: WLANstan Yahoo!: WLANstan MSN: [EMAIL PROTECTED]
-------- Original Message --------
From: Rick Brown
Date: 3/28/2006 8:07 AM
Thanks Stan!
I take it that also means that I shouldn't place two directional antennas
in essentially a Y pattern side by side or one over the under unless
they
are also 3 feet apart?
I have a wide outdoor area to cover (entry to large animal hospital) .
I have
an ideal spot to locate two AP's. However in order to keep outdoor wall
penetrations to a minimum we were going to use one penetration
and place the one antenna pointing southwest and one northwest.
Sounds like I need to rethink this one.
Thanks again!
Rick
Stan Brooks wrote:
When co-locating APs for user density/capacity, they should be on
non-overlapping channels (1/6/11 for 802.11b/g) and should be spaced
some distance (3 feet is a good rule of thumb) apart from one another.
This applies to both 802.11b/g and 802.11a.
The reason you want to do this is to minimize interference between
APs. Even though the APs are on non-overlapping channels, there is a
small amount of RF energy that does overlap and interfere. By
physically separating the APs, this interference is reduced (by
free-space loss) to a tolerable/negligible amount. 3 feet gives about
40 dB of free-space loss at 2.4 GHz to "assist" the guard band
separation between channels.
>>-> Stan Brooks - CWNA/CWSP
Emory University
Network Communications Division
-------- Original Message --------
From: Rick Brown
Date: 3/27/2006 4:51 PM
We are using Cisco 1240 series AP's. I seem to remember
an instructor for Terrawave saying that when clustering AP's
for user density to space them approximately 3 ft a part.
I don't remember if the recommendation applied to 802.11G
or to 802.11A. Does anyone remember any such recommendations?
Example: AP 1 < 3ft >
AP2
3ft 3ft
AP 3 < 3ft >
AP4
Thanks!
Rick
--
Richard E.(Rick) Brown (919) 515-5489 office
Network Systems Engineer (919) 515-1641 fax Communication
Technologies email: [EMAIL PROTECTED]
N.C. State University
********** Participation and subscription information for this
EDUCAUSE Constituent Group discussion list can be found at
http://www.educause.edu/groups/.
**********
Participation and subscription information for this EDUCAUSE
Constituent Group discussion list can be found at
http://www.educause.edu/groups/.
**********
Participation and subscription information for this EDUCAUSE Constituent Group
discussion list can be found at http://www.educause.edu/groups/.
