Feeding an end-fed Zepp

[W Luke Hamaty]

I have been experimenting with end-feeding my wire antenna.
It may be a less-than-optimal arrangement, but it avoids
having 130 ft. of feedline snaking through the house.
The antenna is about 30 meters (98 ft.) long, and I am feeding it
with about 25 ft. of 450-ohm ladderline, one end connected to.
the antenna and the other end dangling/ I am planning to get some
new wire and extend the antenna to 135 ft. Given the layout
of my city lot, the antenna exists in a pretty complex
environment, so I don't assume that the usual factors for
computing the electrical length from the physical length are
very accurate.

What is the preferred way to feed this? I have the ladderline
hooked to the balun connection of a MFJ949E. That seems a bit
odd, but as I understand it, at least the forward and some
portion of the reflected signal is still balanced. (It both
ends were open, the line would be balanced and radiate little.)

Also, the ARRL antenna book, old edition, says that the feedline
on this sort of antenna should not be a multiple 1/4 wave. I
don't understand why not. I thought the classic zeppelin antenna
was 1/4-L tuned feeder and a 1/2-L radiator. Can someone
elaborate on this?

I know this is sort of an old-timer's antenna, but it fits the
circumstances and seems to work. It tunes better than the same
wire did when fed in the center (with 120' of ladderline). I
do have some stray RF problems in the 2nd floor shack, but I
expect that and can deal with it. (The station is so close to
the end of the antenna that I expect a lot of RF around anyhow.)

--
[---------------------------------------------------------------------------]
| Luke Hamaty KQ4OQ "More than gold, I love to complain." |
| Impact Technologies Group - Trurl, from The Cyberiad |
| 704-549-1100 ext. 232 |

[Robert Casey]

In article <39ma3i$f...@news.uncc.edu> wlha...@uncc.edu (W Luke Hamaty) writes:
>Also, the ARRL antenna book, old edition, says that the feedline
>on this sort of antenna should not be a multiple 1/4 wave. I
>don't understand why not. I thought the classic zeppelin antenna
>was 1/4-L tuned feeder and a 1/2-L radiator. Can someone
>elaborate on this?
>

This sounds like a J pole antenna mounted sideways. I would think the
velocity factor of 450 ohm ladder line would be higher than TV twinlead.
Thus the length of the ladder line would be close to 1/4-L * Vf
where Vf is velocity factor, twinlead is around 0.8 or so.

Does this "Zeppelin" (didn't know Led Zeppelin was into ham radio!) :-)
have the feedline coax going to a tap on the ladder line, and is the
non-antenna end of the ladderline shorted together (forms a stub)?

[Greg Dolkas]

Well, my first real Ham antenna was a 3/2 wave end-fed Zepp. Nice antenna -
it's still in service. On mine, however, I fed it with Coax.

The feed line attaches to a 1/4 wave open wire matching section, which
transforms the low impedance of the coax to the high impedance at the end of
the antenna. As mentioned, it's basically a J-pole on its side.

coax feed
===================----------------------------------------------------
|
+-------------

<--1/4 wave--><----- odd halfwave multiple --------->

The open wire 1/4 wave section is made by paralleling the antenna wire with
another wire about 1.5" apart. I used popsicle sticks dipped in wax for
spacers.

I'm not sure how you'd do this with 450 ohm ladder line. Perhaps its as simple
as changing the length of the 1/4 wave section (experiment!), or shorting the
fed end of the matching section and tapping in your ladder line farther up.
One end is 0 ohms (the short), the other end is high (2000+ ohms). 450 must
be somewhere in between.

Good luck,

Greg KD6KGW

[W Luke Hamaty]

In article 5...@netcom.com, wa2...@netcom.com (Robert Casey) writes:

> This sounds like a J pole antenna mounted sideways. I would think the
> velocity factor of 450 ohm ladder line would be higher than TV twinlead.
> Thus the length of the ladder line would be close to 1/4-L * Vf
> where Vf is velocity factor, twinlead is around 0.8 or so.
>
> Does this "Zeppelin" (didn't know Led Zeppelin was into ham radio!) :-)
> have the feedline coax going to a tap on the ladder line, and is the
> non-antenna end of the ladderline shorted together (forms a stub)?
>

It isn't tapped. Any appreciable portion of the wavelength would make for a
pretty big stub hanging down.
A less popular version of the J-pole uses something similar:

------------------------+ Radiator
______________________________________________________________________________________

------------------------+-----------------------
Coax Stub (adj. length to tune)

What I've got is like this:

+------------------------------------------------------------------
|| Wire
||
||
|| 450 Ladderline
||
||
||
+---+
| | Tuner (and balun?)
+---+

Actually, I probably will go back to center-fed. I figured a way to get the feedline around
and up to the shack. The end-fed is giving me RF problems on some bands, which I could
probably get around with some counterpoise. I'll have some even with the center because
the feedline is parallel to the antenna and the antenna is in too imperfect an
environment to really be balanced.

[---------------------------------------------------------------------------]
| Luke Hamaty KQ4OQ "More than gold, I love to complain." |
| Impact Technologies Group - Trurl, from The Cyberiad |
| 704-549-1100 ext. 232 |

[---------------------------------------------------------------------------]