"SparkySKO" wrote in message
oups.com...
My main question is. why is it recommended to run feedline
perpendicular to a dipole?

It helps to prevent RF currents from flowing on the outside of your coax
cable. A dipole antenna is normally a "balanced" type of antenna relative
to earth ground were as coax cable is not. Running the coax at 90 degrees
greatly reduces the antenna coupling to the ouside of the coax but doesn't
eliminate completely enough in some cases.

There are several things you can do to help decouple the feedline, coax,
from the antenna.

1. Spool up several loops of your feedline right at the dipole feed point.
Use a loop diameter of 6 to 8 inches and try around 5 to 6 loops. Hold the
loops in place using some tape or plastic cable ties. What you want to watch
out for is not to make a resonate circuit from the loop inductance and the
stray capacitance between the loops. I guess the way you'll know if this
happens is the SWR will get really screwy and the RF feedback will increase.

2. You can slip a bunch of ferrite ring cores over the feedline right at the
dipole's feed point. You'll have to check for RF heating of the cores, but
at the low 4 watt level you're talking about it likely won't be a problem.

3. You can use a "balum" to convert from an unbalanced feedline to a balance
load, your dipole antenna. You should be able to do a Google search on
"balum" and find something that looks suitable that you can build.

http://www.arrl.org/qex/2005/qx9roos.pdf
http://eznec.com/Amateur/Articles/Baluns.pdf
http://www.qsl.net/iz7ath/web/02_bre.../pag01_eng.htm

Another antenna idea too.

http://www.signalengineering.com/ult...na_basics.html

The URL above has a design for another type of dipole antenna, at the very
bottom of the web page, that should work good for you as well as eliminating
the RF feedback problem. The point here is note the coax is routed through
the inside of the bottom dipole element. This also helps to shield the coax.

--
Regards,
Leland C. Scott
KC8LDO