Hi All... interesting posts on this, what appears to be, somwhat controversial
antenna, the Windom, or OCF dipole if not single wire feed. I just happened to
trip upon this what turned into a balun thread, immediately after I
accidentally stumbled upon the DXE print ad, while searching for W9INN's ads
in a real, not virtual QST magazine. That prompted me to go on-line to
investigate DXE's "New!" baluns.
Two years ago (and still today), I was searching for an inexpensive,
efficient, no radial solution for an antenna. When I first got my ticket again
not long ago, I thought the Carolina Windom to be the perfect magical solution,
given it's claims and reviews. I've come to now believe most of the raves were
the result of awesome propagation associated with the edge of the solar peak of
two years ago, or simply the windom was up a half wave or more, combined with
the fact that two years ago one could truly work the world QRP with rain
gutters, if not literally some wet noodles.
When I finally could accept this, my mind turned to the idea of a classic
single wire Windom, however, Pegasus being my All Purpose rig of choice,RF in
the shack is absolutely intolerable. (I can't do 15m over 20 Watts on my roof
vertical, the computer goes bug-nuts- probably correctable by a change in coax
length, as the air wound choke to augment my home-brew bead "balun" RF choke is
no longer an option, because I wanted to keep the coax as short as possible, I
have not enough slack to roll a choke. Indeed, I IS a Newbie!).
I could add a jumper long enough to make a choke coil for that band, but lately
what I NEED is an 80m antenna with wider bandwidth than my current roof
vertical of the trapped genre sporting 2 radials. So,
Next came the idea of a base fed T, however, at this point, my thoughts were
that now I was into the realms of Verticals, with all their pros and cons.
I rather avoid a wires on the ground if possible. Next came the idea of Cebiks
center fed T, fed with twin-lead, but I knew of no 1:1 curent baluns available
designed for such a purpose. As well, most of my operating time appears to be
rag chewing of the CW variety- DX is fun, but I enjoy chatting a bit, so if DX
chatting a bit can be had, right-on. This seems rare, perhaps there are
language constraints. Most of my rag chews appear to be North American,
sometimes across the pond. So according to Cebiks diagram, T= great DX+ center
fed T= radials won't significantly increase performance, BUT, T= big top-side
NULL (guess that makes it great for DX!). Close in newly made on air friends
might hear me poorly.
So next I thought, unbalanced T, and wait a minute what is that really? Looks
like a classic Windom to me, fed at a 45 degree angle up top at the now Off
Center. But, to crush that idea, there was talk of all this, guess the
experts call them "common mode" currents on my feedline. To boot, I could not
find any data on how such a thing might perform, but I'm thinking the pattern
would be purposefully distorted so as to afford good regional coverage as well
as better than low horizontal wire distance coverage. Such an antenna, with a
properly designed current balun slightly above ground-level might still hold
some experimental promise, perhaps utilizing 1/4 wave counterpoises for each
band of interest (maybe 8 wires on the ground is tolerable).
The idea of a balun or matching transformer of some kind, at an elevated feed
point has never held appeal with me, because of the weight as has been
mentioned, and also because of what I interpreted to be loss associated with
mismatches that would occur at some frequencies. I prefer the idea of having
no balun weight up there, running some sort of twinlead (thinking 300 ohm
windowline), using that feed as an impedance transformer via judicial length
selection, and accepting hopefully undectable by ear, losses- at the tuner-
comprised of components and a circuit design which is intended to minimize
those losses.
I realize I'm sounding very simply minded, but after all, I is a newbie.
I have mostly only read Cebik and ARRL Antenna, and a lot of posts concering
baluns and tuners, geez, some of the debates can sure get hot! Seen a few on
the Top Band reflector when my Uncle was thoughtful enough to forward pertinent
posts to me and I got curious so I went and read the thread.
But, before then, when I first heard of the Carolina Windom, wanted to make my
own, less lossy windom, as I was under the probable misconception that there
might be higher loss than need be in a coaxial vertical radiator, and that two
wires in parallel would have less loss at high SWR while it was doing it's
"radiating." hi hi.
Since then, I've come to believe, that probably the main reason an OCF might
hold value, aside from being convenient, is to avoid extreme impedances when
operating at frequencies away from the fundamental design frequency, in an
effort to minimize losses in places like baluns and tuners when using balanced
feedline.
>From what I can gather, losses are readily available to be had, especially
>within tuners of the T circuit variety "includes built in 4:1 balun" (probably
>Voltage if an older/budget design)- as if to imply this is the end all be all
>you need to connect to your balanced line of a length chosen for the sake of
>physical convenience, completely forgeting the impedance transformation
>properties of feedlines in general. Just hook it up to enough line to reach
>the apex of your all band inverted doublet Vee and you'll be set to go! That
>was my interpretation. Plenty of us non engineer "technologist" type newbies
>out here that read an ad and see it that way.
So now, I'm leaning toward balanced feeline radiation not contributing much
toward the gain of a windom, (though am not entirely convinced at all, that
vertical feedline radiation on a classic Windom contributes insignificant gain
when the single-wire feed approaches a quarter-wavelength or a skosh longer),
and therefore, I am hoping to believe that it may not be significantly
detrimental, in the same vein.
I do believe that for parallel line fed antennas, having no balun at the
feedpoint regardless of how you feed it, in a multiband application, is
probably the best choice.
In searching for an antenna that would offer the most high and low angle
radiation, for an all purpose multiband application, I came upon Cebik's pages
concerning the Center Fed Inverted L. Also read his Antenna's From The Ground
Up. For me, the appeal of the 60-66' per leg inverted L seemed to fit well,
with a good compromise between horizontal and vertical radiation.
I have one tall pine tree, maybe 80' tall, roughly 8' the other side of my
fence. I'm thinking it may serve, as this tree's lower branches have been
supporting my improperly fed 40m OCF wire for 2 years with no complaint. It's
not my tree, how I wish!
But next, I realized, wait a minute, I want 40/30/20/17 and the rest higher
would be nice, too, however that whacko pattern fell. Anyway, a mulit-high
band horizontal dipole would be doable later in the early summer, vertical GP
even, heck, even bite the bullet and get a GAP Titan, it covers the high bands,
but- the big wire antenna must do 17m on down, because with 4 kids who knows
when I'll be able to justify even but 320 bux on a Titan?
I am no mathmetician- and looking at a most basic graphic of current/voltage
distribution, and also evidenced by the theoretical feedpoint figures Mr. Cebik
included with his All Band Inverted L compendium- I'm back to square one:
Feeling the need to avoid extreme impedances. Which of course on 40 and 20, the
center fed 80m 1/2 wave dipole has plenty to offer.
At this point I came full circle, and, as I already cut my 160m G5RV to OCF 80m
length and will soon hack the coax off, I came to the conclusion that perhaps,
this might work better for me, with an appropriate feedline length. The end of
the horizontal leg may have to dangle 10 feet or so, and the "horizontal" leg
also would have to be slanted- apex around 70' (i hope!), the end of it at
about 30'. The vertical leg would simply dangle from 70' mostly vertically,
depending on the wind.
Whether or not I'd end up using one of the, for me, overkill expensive but
probably worth it DXE baluns, remains to be seen, as the tuner I plan to use
already has a 1:1 currrent balun- the tuner I'm thinking about is an auto tuner
Pi-L depending on reactance values. I have no amp nor designs on obtaining one
any time soon. Mostly, I hear guys with amps calling CQ and often are unable
to hear the people answering, and for the ones they do hear well enough to call
back, 80W would have worked almost as well anyway. Nothing against amps and
their use, perhaps some day.
So there it is, the whacko and unconventional OCF inverted L.
Any thoughts, comments, jokes, hoo-hahs or poo-poos are appreciated.
Thanks in advance
73.
Darin, W3DCG, Newbie in Atlanta.
---------------------------------
Do you Yahoo!?
Yahoo! Hotjobs: Enter the "Signing Bonus" Sweepstakes
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|