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Vertical separation in antennas

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November 27, 2004 2:19:58 AM

Archived from groups: alt.internet.wireless (More info?)

I have 2 SA24-120-16 antenna's on a tower. Still learning alot about
wireless broadband as I go. currently they are at the same height on the
tower and near each other. Can this cause interference and if so, how far
apart should they be vertically and horizonatlly. They are set for a
vertical polarity.

Thanks!
Anonymous
a b F Wireless
November 27, 2004 7:04:45 PM

Archived from groups: alt.internet.wireless (More info?)

On Fri, 26 Nov 2004 23:19:58 -0800, "me" <here@i.am> wrote:

>I have 2 SA24-120-16 antenna's on a tower. Still learning alot about
>wireless broadband as I go. currently they are at the same height on the
>tower and near each other. Can this cause interference and if so, how far
>apart should they be vertically and horizonatlly. They are set for a
>vertical polarity.

Antennas do not cause interference. Radios cause interference.

So far, all I know is that there are two antennas on a tower at some
unspecified seperation and orientation. No clue as to how much coax
is between the antennas and their respective radios, what type of
radios, length of coax cables, and whether this is part of some power
splitter or amplifier arrangement.

The RF-Linx SA24-120-16 is a 120 degree sector antenna, with 16 dB of
gain. If you mount these next to each other, but rotate them so that
the 120 degree sector pattern does NOT overlap, you will probably have
enough isolation between antennas. If you look at the typical
cellular monopole, that's the way they do it. 3ea 120 degree sector
antennas wrapped around the pole.

The point at which your unspecified receiver overloads is in the data
sheet. -30dBm is typical. If you do have overlap, you can use the
antenna patterns:

http://www.rflinx.com/Antenna%20Datasheets-html/2.4GHZ/...
to estimate the amount of signal coupling between antennas.
http://my.athenet.net/~multiplx/cgi-bin/isolation.cgi
Subtract out any coax losses, and estimate how much signal is
appearing at the receiver from the other transmitter. If over perhaps
-30dBm, you will have a desensitization problem. Note that the
interfering transmitter does NOT need to be on the same channel.

A more serious and incidious problem is intermodulation products
caused by two transmitters mixing together. This can easily happen
when two or transmit antennas are too close. In commercial VHF/UHF
systems, isolators, circulators, and cavities are used to provide
additional isolation. These are not very economical at 2.4Ghz, so
physical isolation is necessary.

Rant: Numbers and specifics, not prose.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
November 27, 2004 7:12:05 PM

Archived from groups: alt.internet.wireless (More info?)

"me"
| I have 2 SA24-120-16 antenna's on a tower. Still learning allot about
| wireless broadband as I go. currently they are at the same height on the
| tower and near each other. Can this cause interference and if so, how far
| apart should they be vertically and horizontally. They are set for a
| vertical polarity.

I'd need a bit more info to make an educated response but with what you have
posted:

Horizontally spaced antenna typicallky experience more mutual interference
than vertically spaced antenna. The idea configuration would be vertical
spacing coaxially in line.

That said there are two type of potential interference. The first has to do
with RF reception and is frequency/channel dependant. The second has to do
with parasitic reradiation. In some cases this is the desired effect and
produces directivity. In other case it can cause multi-plathing which is
typically (but not always) undesired.
Related resources
Can't find your answer ? Ask !
Anonymous
a b F Wireless
November 27, 2004 8:39:58 PM

Archived from groups: alt.internet.wireless (More info?)

Sector antennas dont have near the problems as other antenna types. I see
sectors on antennas all the time
mounted 6 at a time. Are you experiencing interference or just curious. Are
they on the same channel?


"Not Me" <me@privacy.net> wrote in message
news:30s9c7F34mlkaU1@uni-berlin.de...
>
> "me"
> | I have 2 SA24-120-16 antenna's on a tower. Still learning allot about
> | wireless broadband as I go. currently they are at the same height on
the
> | tower and near each other. Can this cause interference and if so, how
far
> | apart should they be vertically and horizontally. They are set for a
> | vertical polarity.
>
> I'd need a bit more info to make an educated response but with what you
have
> posted:
>
> Horizontally spaced antenna typicallky experience more mutual interference
> than vertically spaced antenna. The idea configuration would be vertical
> spacing coaxially in line.
>
> That said there are two type of potential interference. The first has to
do
> with RF reception and is frequency/channel dependant. The second has to
do
> with parasitic reradiation. In some cases this is the desired effect and
> produces directivity. In other case it can cause multi-plathing which is
> typically (but not always) undesired.
>
>
Anonymous
a b F Wireless
November 29, 2004 3:48:56 AM

Archived from groups: alt.internet.wireless (More info?)

Simply, in theory you should place your antennas about 120-300cm horizontally
from each other, and at least half of their length in vertical.

This is, of course, only theory. Everything depends on your radio's output
power.
When talking about wifi I think that a couple of centimeters is enough.
(tested)
But it also depends on antenna's F/B ratio...

m.


--
Marcin Lukasik
Milea Wireless Communications, http://milea.pl
phone/fax/mobile: (++48) 13 4480070 / 13 4481148 / 509 390 490

,,the only difference between men and boys is the price of their toys''
!