On Sat, 03 Jan 2004 18:38:59 GMT, "Vaughn Combs"
wrote:

I have a few questions and I thought that this may be the group that could
help. I have a nice sized backyard and would like to construct an antenna
that would give me good performance on 80-10m bands.

The convenient dimensions would put a support (far end) at either 92 feet
from the back of the house (support exists that is about 15-20 feet up) or
120 feet from the back of the house (mast anchored to the other side of a
shed could easily be installed. Or a more inconvenient support could be
erected up to 300 feet out (no support buildings) at the absolute far end of
the property. The width of the property as seen looking out the back window
is about 65 feet (no supports existing on either side).

Special circumstances and constraints:

-- No tall trees on the property.

-- Attic shack (attic window is probably about 25 feet up). Need to keep to
the attic.

-- Cable run from back of house to operating position within the attic would
be approximately 25 feet

-- MUST eliminate RFI in the shack and house.

My current setup is an end-fed longwire that works well on all bands except
40m (rig shuts down as I am dipping the SWR to almost 1:1 ;-). I threw up
the wire as winter was upon me. I have been off the air for almost 10 years
and REALLY wanted to get on the air again.

While the longwire is performing quite well with the exception of 40m I am
getting a ton of RF in the shack and it is blanking out TVs and creating
loud humming in speakers with 100W from the XMTR. I realize that this is
most likely due to the fact that I have inefficient RF ground and I have cut
and run radial at 1/4 wave for each band and ran them under the eaves up
here in the attic. This has not solved the problem. I am friendly with all
of my neighbors and have visited them and did testing on the bands with them
on the phone. They are not experiencing any problems. My wife, while
understanding, would REALLY like the problem to go away ;-)

My main goal is to build an antenna that will solve the aforementioned RFI
problem and that will provide good performance given my constraints.

Any ideas would be GREATLY appreciated.

Many Thanks and 73,
Vaughn
N2BHA


Hi Vaughn,

Your first shot is probably your best shot. You should drop a line
from the near end antenna anchor point directly down to a ground and
rely on a tuner to make up the differences. From the anchor point
(where both wires are broke out) install a 1:1 Current Balun (Choke)
between these points and the transmission line back to your rig to
eliminate some of your noise into the house, and to get rid of the 40M
instability (a classic symptom of Common Mode whose cure is in the
Choke). The "ground" lead will radiate, but that is inconsequential.
You may also experience a ground loop with it in parallel to your
rig's source of ground.

This is the blind-side of many hams who forget that long ground wires
have impedance and thus become miserable grounds for RF. Unless you
work battery operation without a floating charger, you WILL have this
second path to ground (the 'trons will find their own way, even if it
isn't obvious to you). I always run battery with a float charger
through an 1:1 isolation transformer to kill Mains borne noise; and
whenever I experience ground loops, I simply disconnect the charger.

73's
Richard Clark, KB7QHC