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Author Topic: End Fed - HF multi-band - What's the real story?  (Read 4413 times)
KC9KEP
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« Reply #15 on: September 22, 2009, 07:00:17 PM »

I've got a dumm question ..

When one specifies the length of an end-feed L-antenna,
are they referring to only the horizontal part, or
is the vertical "lead in" part of the measurement as well?

Thanks! & 73
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WB6BYU
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Posts: 13247




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« Reply #16 on: September 22, 2009, 10:55:48 PM »

Generally the overall wire length, since that (to a large
extent) determines the current distribution on the wire
and the matching method needed.

But the height of the vertical portion affects the
performance as well:  generally higher is better, since
the inverted L is generally intended for low angle
radiation on the lower bands (80 and 160m.)
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K0CWO
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« Reply #17 on: September 23, 2009, 11:21:00 AM »

Here is my story.  I have a cabin that sits on a lot that slopes down toward the lake.  I use an IC-7000 driving an AL-80A and an ATR-30 antenna tuner.  I ran a 200 foot piece of insulated wire from the single wire post on the antenna tuner through a panel in the shack sliding window.

From the window the wire runs 20 feet up to a tree limb, then 100 feet horizontal to another tree, and then it slopes 80 feet down where it is tied off to a tree trunk using nylon cord high enough so nobody can touch it.

I ran two 200 foot counterpoises lying randomly on the ground in different directions which are connected to the ground post of the tuner.  The wire tunes 160-10.  I use it mostly on 160, 75, and 40 for local rag chew purposes.

Compared to my 230 foot doublet 40 feet of the ground at home 60 miles away, the end fed wire is certainly not as efficient. People on 75 meters can tell that I'm at my alternate QTH, typically getting 10 to 20 over S9 signal reports, where at home I typically get 20 to 30 over s9 reports running 800 watts with similar band conditions.  On 160 and 40 meters the results are about the same.

I used neither math nor reason to use 200 feet of wire.  I ended up using that length because it was an easy fit for my particular situation.  The antenna and counter poises took less than an hour to construct and the wire has been up for a year surviving several storms.  I am planning on replacing the end fed wire with an open wire fed loop this fall.  If for some reason I don't get to that project, the 200 foot end fed will suit my hobby at the cabin none the less.

It is no barn burner, but it gets me on the air.

73, k0cwo
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K8QLW
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Posts: 37




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« Reply #18 on: September 25, 2009, 08:31:24 AM »

It's one of those very busy days so I haven't read the other responses. I apologize if I duplicate someone else's reply.

I had the same need as you when I was stationed in Yuma, AZ.  I had worked with bringing wires into the shack with mixed results at other QTHs so I decided to match the random wire (20 feet vertical and 75 feet horizontal) remotely at the feed point with an MFJ tuner in a water proof box (Plastic handgun case) and run coax to the shack.

I'd key up on frequency with about 10 watts, walk out to the tuner, adjust for 1:1, return to the shack, give my ID.  Then I was set for that frequency on 80-10M.  What I found is that it worked great!  In addition my band width (< 2:1) on 40 and 80 was quite a bit greater than with a center fed dipole.

I tried using a ground rod at the transmatch and found that it was not needed.

Hope this helps,
kent
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W5DC
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« Reply #19 on: September 25, 2009, 10:58:30 AM »

Long ago in the pre-WARC band days, I used an end fed inverted L that was a quarter wave long on 160 with some added stubs to keep the angle of radiation low on 20, 15, and 10.  I tuned all bands with a simple, suitably tapped shunt inductor and a series variable capacitor, mounted at the point where the "wires", 3/8" by 24 tpi SS rod, came through the brick wall of my shack.  On each band, I used a single quarter wave counterpoise that followed the outside walls of the house about eight feet above the ground with no problem with RF in the shack whatsoever.  Using a single elevated counterpoise can work quite well compared to using a limited set of ground wires.  

73, Dunc, W5DC
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W5DC
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« Reply #20 on: September 25, 2009, 12:20:18 PM »

If you use counterpoise wires close to, on, or against as structure, you may need to shorten the counterpoise wires to compensate for the dielectric effect of the structure.  What I did was to cut a second dipole half according to standard formula and then trim the counterpoise wire for resonance.
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