[Elecraft] feeding a half-wave dipole with ladder line

[Jack Brindle]

Ed;

Bob’s advice is still sound. The ladder or open-wire line is quite simply, a transmission line. As all transmission lines, it will transform the impedance it sees at the antenna end to some other value at the tx end. The transformation will be highly dependent on frequency, length and line characteristics. The advantage of open-wire (my favorite) is that because the loss is so low, you don’t care that much about the length or the actual transformation. Like Bob, I also use a 1:1 balun and let the ATU perform the necessary matching. The impedance of the open-wire line really doesn’t matter in the situation as far as baluns are concerned. 

I also have several other tuners, including an old swinging-link type I build many years ago that actually does a better job of matching. It, of course does not need a balun. Unfortunately my manual tuning cannot come close to the time my KAT500 takes to perform the auto tune, especially if I train it ahead of time.

One other thing I would add. I don’t really try to cut my open wire or ladder line fed wire antennas to any specific length, but rather cut them for whatever space I have and let the ATU handle the matching. In fact that is the approach I will be taking tomorrow as I put up antennas at my new QTH here in Louisiana. Getting ready for CW Sweepstakes, but the tower and beams will have to wait for next year...

73,
Jack, W6FB

> On Oct 30, 2021, at 6:25 PM, Ed Cole <kl7uw at acsalaska.net> wrote:
> 
> Bob,
> 
> Either you did not read what I wrote carefully enough, or I did a poor job of explaining.
> 
> First off:  I an not a HF DX chaser or HF Contest junkie.  HF is a very occasional activity when I want a casual chat or check in a local net.
> Thus a compromise antenna for the "low bands".
> 
> The existing 80/40m dipole is a fan dipole with 80 and 40m wires.  I plan the new setup  to run 40m at right angles for less interaction between them (been there done it experience).
> 
> If all I wanted to do is 80/40 I would install the existing 1:1 balun at the feed and run coax to it.
> 
> But I was thinking I could use window wire (commercially made) instead of the 12-inch parallel wires I show in the diagram.  Whatever its impedance (probably like 300-ohm or 450).
> 
> By shorting the ladder line I could feed the antennas as a shortened vertical on either 160m or 630m where the dipole wire would add "top-hat" loading.  Similar to how the horizontal wire in an inverted-L works.
> 
> I already have my 630m loading coil to use at the base; adding a tap it could work at 160m.
> 
> I have vacuum relays to do the shorting.  And yes there will be radials that are too short on 630m (1/4 wave is 522 feet and my property is 200x 300 foot).
> 
> My question regarded choosing a proper balun to use on 80 & 40m. Running 140 foot of ladder wire on diagonal to the shack defeats using it as a vertical.  Ideal would be a QRO ATU at the ground-end of the vertical wires (but I'm too cheap for that).  I have a QRO Drake Tuner to do the job at the shack.  I'll try out my 1:1 balun.
> 
> 
> 73, Ed - KL7UW
> 
> Date: Fri, 29 Oct 2021 18:48:36 -0500
> From: Bob McGraw <rmcgraw at benlomand.net>
> To: elecraft at mailman.qth.net
> Subject: [Elecraft] feeding a half-wave dipole with ladder line
> Message-ID: <8431998e-509b-9164-368a-1985394d87f6 at benlomand.net>
> Content-Type: text/plain; charset=UTF-8; format=flowed
> 
> 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
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