----- Original Message -----
From: "Mac Dearman" <[EMAIL PROTECTED]>
To: "'WISPA General List'" <[email protected]>
Sent: Friday, May 18, 2007 2:01 PM
Subject: RE: [WISPA] 180* sector choices
Inline again :-)
Behalf Of Jack Unger
Mac,
Thanks for replying to my concerns and suggestions.
Have you tried using 5 to 10 feet of vertical separation between the
antennas rather than mounting them all at the same height? 10 feet of
vertical separation should be enough to prevent one AP transmitter from
overloading another AP receiver.
[Mac says:]
Now you are talking the "Jack Unger" talk that makes me sit up and take
notice :-)
I have not tried the vertical separation because it looks so
unprofessional
(although is a professional move) to have 3 sectors spread out over thirty
feet and it also puts 2 of my three sectors at a disadvantage due to the
height loss. We cover a lot of rugged territory, conquer (really not very
well) massive 90' Oak trees and connect subs as far as 20 miles off these
towers. It is a fine idea and one I may have to move to!
I've got some that are within a few feet of each other. Also have some that
are RIGHT behind others.
We're having some problems at that site that sure act like interference.
I'm pretty sure at least some of it is self inflicted. How much there's no
good way to tell. They are all the higher end Maxrad sectors.
I'm going to get long lmr600 runs (50/40 and 30') and make sure that the
radios are all down at the ground where I can get to them with a ladder, and
I'll make sure that the antennas are all 10' or more apart.
We're going to rebuild two sites in this manner.
Secondly, single-channel bandpass filters are available which will
provide additional receiver protection from nearby transmitters
operating on non-overlapping frequencies.
[Mac says:]
That sounds like the way I will go. I appreciate the idea and suggestion.
I
don't know why I haven't thought of that before. I guess I have never
bought
or even had need of a bandpass filter till now. Well truth be known it
seems
I have needed them for years, but didn't realize it till today.
I don't use bandpass filters. I have to change channels far too often for
that. I'm finding that some radios are far more effective in their
isolation than others are. I'd also rather use antennas for my isolation
than having another device I have to worry about inline.
Finally, higher-priced antennas normally have a higher front-to-back
ratio which increases isolation (minimizes interaction) between the
antennas. A minimum f/b ratio of 30 dBm is recommended.
[Mac says:]
We have always bought and used PacWireless antennas and thee 16.5dbi 120*
VPOL sectors have at least a F/B ratio of 25db. I realize the more you
spend
the better F/B ratio you get and that is where my original thread
started -
- looking for some good sectors :-)
TilTek was brought up. Those are good. So are radio waves. I've been
REALLY happy with the vpol ($425ish) and hpol ($250ish) Maxrad adjustable
beam sectors. I like the flexibility for the future too.
marlon
Keep in mind that without dealing with these antenna isolation issues,
you will likely have the same problems using two 180* sector antennas as
you have had using three 120* sector antennas.
[
[Mac says:]
That is fine advice Jack and I appreciate the fine guidance. You have made
me think - - and that may be a dangerous thing. Now - - let me go order
some
bandpass filters and hang them on one of these troubled tower to see what
is
gonna happen. I will post back here and let you know my results.
Thanks again Jack!!
Mac Dearman
jack
Mac Dearman wrote:
> See in line please
>
>
>> Behalf of Jack Unger
>>
>> Mac,
>>
>> Before you discard the idea of using three 120* sectors are you
>> absolutely certain that the "separation" issue is really due to the
>> antennas not being far enough apart? Have you thoroughly looked at
other
>> reasons why there could be interference between three APs like:
>
>
> [Mac says:]
>
> Well Jack - I'd like to think that I have exhausted the other
possibilities
> :-) but I am always willing to listen.
>
>> 1. Using three cards on a single motherboard in one enclosure without
>> sufficient shielding between them.
>
>
> [Mac says:]
>
> All of our sector arrays utilize 3 different enclosures with one radio
to
> the enclosure and then I try to separate the enclosures (and antennas)
as
> far as possible.
>
>> 2. Using three APs that are configured on frequencies that are too
close
>> together and are interfering with each other?
>
> [Mac says:]
>
> Unless we deploy 4 90* sectors we use non overlapping channels (1, 6 &
11)
>
>
>> I guess what I'm asking is (before you go spend money on antennas that
>> may or may not solve the problem) what equipment are you currently
>> using, how is it configured, and how far apart can you actually get
>> three sector antennas on the 25G tower?
>>
>> jack
>
> [Mac says:]
>
>
> I have come to the conclusion that it is interference from the
backplane of
> the antennas due to not having adequate separation from each other.
These
> small towers (although 180') like Rohn 25G aren't but 12" across - so
you
> wind up with the 3 sectors only 1' apart at their bases.
>
> I wish you had some more ideas :-), but thanks for the thought and the
time!
>
> Mac
>
>
>
>
>
>
>
>
--
Jack Unger ([EMAIL PROTECTED]) - President, Ask-Wi.Com, Inc.
FCC License # PG-12-25133
Serving the Broadband Wireless Industry Since 1993
Author of the WISP Handbook - "Deploying License-Free Wireless WANs"
True Vendor-Neutral Wireless Consulting-Training-Troubleshooting
FCC Part 15 Certification for Manufacturers and Service Providers
Phone (VoIP Over Broadband Wireless) 818-227-4220 www.ask-wi.com
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