Remember that you are not matching the impedance of the ladder line, but
more so, matching the impedance of the antenna. The reason for ladder
line is the low loss property even with high SWR on the line. A good
quality 1:1 balun is preferred. See https://www.dj0ip.de/balun-stuff/
I've been using balanced fed antennas since 1960. I bring the balanced
line all the way to the tuner in the shack where it meets up with my
custom Guanella balun. Regarding balanced fed antennas, they work, they
are easy to use, easy easy to keep in the air and DO NOT have TVI or RF
issues in the shack. Most of the information you hear is related to
"old ham lore" and is not valid in any sense of the imagination.
Yes, the 130 ft center fed length will be very difficult to match on 40M
as the feed Z will be very high, in the order of 4K ohms, and not likely
in the range of your tuner. I suggest you add a 33 ft section of wire
to either side at the feed point. Thus a 80/40M antenna. Then you
will be able to work 80M, 40M, 20M, 15M, and 10M with that antenna
configuration. Mine does! Works great.
If you want it to work 160M then it needs to be 256 ft in length.
Although you might get a reasonable match on 160M with the 130 ft center
fed wire. It will depend somewhat on the feed line length acting as a
line section transformer.
As to 630M, that is a different animal and needs special attention. I'd
suggest tying the feeders together and uss the antenna as a top loaded
vertical.
73
Bob, K4TAX
On 10/29/2021 4:59 PM, [email protected] wrote:
Message: 3
Date: Thu, 28 Oct 2021 13:23:23 -0800
From: Ed Cole<[email protected]>
To:[email protected]
Subject: [Elecraft] feeding a half-wave dipole with ladder line
Message-ID:<[email protected]>
Content-Type: text/plain; charset=UTF-8; format=flowed
I am redesigning my 40/80/160/630m antennas.
A year ago the tower I was supporting my 630m Invert-L was damaged by
wind and taken down. Replacement tower is shorter so not suitable end
wire support for HF antenna.
I decided to repurpose my 80/40m dual dipole into a based-loaded 40-foot
vertical using the 80 & 40m wires for top hat loading on 160/630m. To
do that I purpose to run 40-foot of ladder-line vertical and either load
the bottom using a balun for 80/40m or short the ladder line for the
loaded vertical.
http://www.kl7uw.com/630mTee.jpg
My question is what balun to use for 80/40m. ladder line is 200-300 ohm
whereas the dipoles are near 50-ohm. Should I use a 9:1 balun or would
my original 1:1 balun work? Tuners will be in the shack (KXAT at 100w;
Drake MN-2000 at 1200w). RG-13 coax to base of ladder-line.
I have a couple vac-relays to short the ladder-line and connect the
loading coil for 160/630m.
Thanks, Ed - KL7UW
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