[Antennas] Question on open wire feeders and RFI/TVI

[Robert Lay - W9DMK]

On Tue, 22 Apr 2003 08:19:20 -0400
 "N1DVE Jacqui" <n1dve@attbi.com> wrote:
> Are antennas that are fed with open wire feeders more prone to RFI or
> TVI
> than those using coax?

Dear Jacqui et al,

Most RFI and TVI problems are due to overloading or just plain "too
much RF" and can be reduced significantly by just moving the radiator
as far from the sensitive items as possible. For example, I found that
having a dipole about 75 feet away from the house was far superior to
having it directly overhead.

When it comes to the xmission line itself, the question of coax vs
balanced open wire or twinlead is mute. Either one can have severe
problems due to a poor grounding configuration and unbalanced current
flow on the xmission line. For example, the amount of RF on the outer
shield of a coax line has to get to earth through some pathe.
Typically, it finds a path through the house wiring and through the
equipment in the ham shack - not where you wanted it to go. Balance
feed lines are less likely to have that problem - especially if
connected via a link-coupled tuner, but it can still occur. If you have
to make a transition from balanced line to coax or unbalanced circuits
at some point, using a balun, it is a good idea to keep that outside
and get the shield well earthed before it comes into the shack.

73 de W9DMK (Bob Lay in Dahlgren, VA)
http://www.qsl.net/w9dmk