[Cliffdwellers] Coaxial-Trap Multi-Band Attic Dipole

[Linden, Mike (BRC-Hes)]

  Just in case there are some people who weren't aware of it, but might be
interested, there is a good article by John De Good, NU3E, on the design of
a Coaxial-Trap Multi-Band Attic Dipole that covers the bands from 10m - 80m,
excluding 60m.

  I am currently using a version of this antenna that covers 10m/15m/20m/40m
(about 40 feet long) in the attic of my 2-story house. My minimum SWRs vary
from about 1.3:1 on 40m to about 2.4:1 on 20m (the higher minimum SWRs are
no doubt an issue of interactions with conduit, foil-backed insulation, and
wiring in the attic). However, the antenna does seem to be relatively
broad-banded and my Kenwood TS-930S' internal antenna tuner has no problem
giving me the ability to work the entire spread of each band. It should be
noted that I previously tried a multi-band fan/parallel dipole in the same
attic and found the bandwidth to be much smaller.

  I plan to add a 30m section to the main dipole and add 12m/17m coverage
via a perpendicular dipole coming off of the same balun feed point (as noted
in the article).

  I realize that traps can be lossy and reduce the length of the dipole due
to loading. However, you must be willing to make tradeoffs when dealing with
attic antennas. And, without the inductive loading of the traps, I wouldn't
be able to fit a 10m - 40m dipole in my attic anyway (hi)!

  If anyone is interested, the article can be found at:

http://users.tellurian.com/jdegood/coaxtrap/

  73, Michael N9BDF