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/RFLSA24%20VERTICAL%2090-120%20SECTOR.htm
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