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Re: Center-fed antennas

Posted by Vic Rosenthal on Oct 11, 2019; 5:54am
URL: http://elecraft.85.s1.nabble.com/KX2-Antenna-Curiosity-tp7655612p7655649.html

Things I’ve learned by experience:

In 63 years as a ham, I’ve had several :-) HF antennas. The ones that gave me the greatest overall satisfaction have been balanced, horizontal antennas. The worst have been verticals with inadequate radial systems or low random-length wires. Inverted Vs with angles less than 90 degrees between the wires are not much good, either.

There is no simpler way to make an efficient multiband antenna than to feed a dipole of at least 1/2 wavelength at the lowest frequency with open wire line. With some care in choosing the length of the line, a 1/4 wave dipole can work almost as well. I’ve worked over 300 countries on CW in the last 5 years on the bands from 40-10m with a 10m long rotary dipole, in an urban area (it is up 35m on a building and I run a kW, I admit). I regularly bust pileups on 40m with it.

1:1 baluns work to feed open wire lines, but can become inefficient in some circumstances and heat up. It’s possible to solve this by compensating for reactance with a pair of capacitors or inductors before the balun, but a better solution is a true balanced antenna tuner.

“True Ladder Line” is a good product, but it’s easy to make your own, and you can use no. 12 (2 mm) wire for lower loss.

Sometimes a 4:1 balun may give a better match, but it will be less efficient (heat) and do a poorer job of keeping RF out of the shack.

Nothing has worked better for me at cleaning up RF in the shack than an old Johnson Matchbox, a true balanced tuner.

Victor 4X6GP

> On 10 Oct 2019, at 23:56, Lyn Norstad <[hidden email]> wrote:
>
> I'm having great success with a horizontal center-fed "dipole" that has been sized (360 feet long) to be an Extended Double Zepp (4.7 dbi gain) and cut for the low end of 80 meters.  I feed it with 600 ohm "True" Ladder Line from a Balun Designs Hybrid Balun (1:1 Current and 4:1 Voltage all in one case).  A short run of coax from the balun to my KAT500, and I am in business at any frequency on 160 - 6 meters.
>
> It's oriented to be an effective NVIS radiator in a N-S pattern on 80m, by design, and to have major lobes on the other bands in other directions - also by design.  For me, it's the most efficient and effective way to utilize our lot space (400 feet clear) and still be "under the radar" in our HOA.
>
> Birds seem to like it, and I find that it seems to be especially attractive to Hummingbirds, my XYL's favorites.  A win-win, in my book.
>
> 73
> Lyn, WØLEN
>
>
> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On Behalf Of Al Lorona
> Sent: Thursday, October 10, 2019 3:25 PM
> To: [hidden email]; David Gilbert
> Subject: [Elecraft] Center-fed antennas
>
> My experience with single vertical or sloping wires is exactly the same as AB7E's. I have, over almost twice as many Field Days as Dave, come to a similar conclusion, with the slight difference being my preference for an "all-band dipole" fed with balanced line. This obviates the balun and reduces feedline loss to negligible, so obviously I am maximizing efficiency at the expense of any other possible advantage. (I can usually hear much better than I can be heard... so thus far this has been a valid decision.)
>
> To sum up what I and what I think Dave are saying, you can't beat a horizontal, center-fed wire up as high as you can get it. Its simplicity, the flexibility it gives you to QSY (with a good tuner), and its high efficiency are almost unbeatable.
>
> As a side note, the center-fed horizontal wire I have used here at home is totally non-resonant. I don't even know how long it is. Once you give up the obsession with resonant antenna length, you gain a huge freedom of choice.
>
> In the bottom of the sunspot cycle, these advantages are somewhat reduced because an op, especially on Field Day, might opt to forget about any band higher than 20 meters -- and these days even 20 is questionable. This means you can probably make do with coaxial cable and a balun for operation on 2 or 3 bands but the general idea still holds.
>
> Al  W6LX
>
>
>> Yes, a center fed normal dipole with the middle (high current portion)
>> higher off the ground (say 50 feet for 40m) and a common mode choke at
>> the feedpoint would almost assuredly perform better.
>>
>> 73,
>> Dave   AB7E
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