Jeff
Answering your last question first:
for top band and 80m mainly (actually, it worked on all bands) I joined the
feeders together into one terminal of my Drake tuner and the other I took
thro some tv coax (shorted) back up thro the ceiling, out to the soffit
board and straight down to a ground spike (brass curtain rods) and lots of
radials in the front garden. This was then a heavily top loaded vertical
and worked very well. The single outdoor brown wire spaced off the brick
wall about a foot was almost unnoticeable and a friend thought it was just
the tv coax that had come unclipped.
Back to the invertedV/doublet/loop bird's nest: I could model it in EZNEC
if I had a few minutes, but I am sure the results will be impenetrable:
there will be lobes going in all sorts of directions at all sorts of angles.
What will be a problem is modelling the house and structure which is beyond
me. Frankly, as the man said: I don't give a d*mn. As radio amateurs we
are interested in getting signals in and out and the performance of simple
antennas is just the joy of working the world and that's what I did. Be
aware of the noise picked up from the house mains and the interference you
can put into the mains. I used to modulate the lights on 20m. Look out for
high voltages - use heavy gauge insulated house wire (it's more efficient)
and insulate any bare wire ends.
As to shorting or opening the ends: it changed the range of frequencies that
could be matched. I started making a table of strength of signals from
various directions with open or short and with feeding from corners or apex,
but the combinations were endless and of course change endlessly with
frequency and band conditions. I gave up after a few trials. In its
vertical configuration I got more dx which was to be expected and I think I
left it like that.
Just enjoy getting out.
David
G3UNA
----- Original Message -----
From: "Jeff" <[EMAIL PROTECTED]>
To: <elecraft@mailman.qth.net>
Sent: Saturday, October 28, 2006 9:19 PM
Subject: [Elecraft] Attic Ant.-Closed Loop vs. Open Ends?
David, G3UNA, wrote:
...My 'doublet' was nearly a loop, ie it followed
the beams around the loft. The ends were left open, about a foot
apart...
I have some questions for the group. How would one decide whether the
ends
should be left open, versus connected together to make a loop? (I never
could figure out how to model antennas using EZNEC. It should be called
HARDNEC.) Does it make a lot of difference? Using a tuner near the
feedpoint, which way would give a better match on more bands (160-10m),
open
or closed ends? Which way would yield stronger signals in the most
directions? Is it the case that, below a certain total wire length, the
ends should be left open, but above that length, they should be connected
together? I guess the only way an indoor antenna of typical length would
match on 160m, even with a tuner, would be if the ends were connected
together and the whole thing was treated as a very bent end-fed wire
working
against ground and a counterpoise.
Thanks & 73,
Jeff, WB5GWB
Long Island, NY
K2 #821
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