RadioBanter - View Single Post

Roy Lewallen · December 15th 06, 09:48 AM posted to rec.radio.amateur.antenna

wrote:
Hi all,

I have two omni dipoles @ 2.4Ghz, one positioned for vertical
polarization and the other horizontal.

What's an omni dipole? How does it differ from an ordinary one?

I have stiff coax feeding these
two antennas. The horizontal antenna is above the vertical, and the
coax feeding the horizontal runs pararellel with the vertical antenna
around 2 wavelenghts (24cm) away. My question is will the signal on
the coax leak onto the vertical antenna?

If you want to make your system sensitive only to one polarization at a
time, the first thing you need to do is to prevent any signal from being
on the coax in the first place. This can be done by running the coax
symmetrically at right angles to the dipole (assuming it's something
like a conventional dipole) to prevent current by induction, and adding
a "current" or choke balun at the feedpoint to prevent current by
conduction.

I want the two to be as
orthogonal as possible. I'm not really sure on the physics involved
but is there a standard seperation that is required to minimize this
effect or will they always be coupled if I run the lines in this
manner? Thanks for any info,

You'll prevent coupling by taking the steps I mentioned, and keeping the
lines at right angles to each other and keeping each symmetrically
placed with respect to its dipole.

Roy Lewallen, W7EL