[TenTec] [Ten Tec] OCF Antennas - Which commercial antenna is gest?
k3ndm at comcast.net
Tue Sep 22 19:04:11 EDT 2015
I think there is some historical perspective that is missing in some our
discussions. First open wire was used in the early days of radio as
there wasn't much else around. You could run a wire from your antenna
directly to your transmitter's output, but there were really few other
ways to go. Coax came into being somewhere around 1940, and this can be
disputed, for the purpose of running a transmission line through a
ship's steel bulked. The 50 Ohm number came about because that is what
resulted from the material at hand, or you can supply another story.
The Windom was invented to be able to use a single antenna on multiple
bands. The original design shows that it was fed by a single wire to a
point 1/3 down the length of the antenna, and it was mandatory to ground
the radio. All of what we today call Windoms or OCFDs are based on
Windom's design. None of any of these antennas were touted to be 50
Ohms. They were sold to be workable with your transmitter if you have a
tuner, and hopefully a good one with reasonable loss. One commercial
version sold by Radio Works is the Carolina Windom which is a design
that a bunch of hams in the Carolinas came up with based on Windom's
designs. From my inference, what they were trying to do was to overcome
the issue of having a horizontal antenna electrically low to the ground
and still get low angle coverage. It sort of does that, and I said in an
earlier post I bought into that argument; I'm not sorry as I was finally
able to obtain a DXCC after 50 years on the air. The Windom is not a
compromise antenna unless you consider trying to use one antenna for all
bands a compromise. I make NO consideration for SWR.
I am very cavalier about SWR as a means of determining an antenna's
operation, except in the extreme. A 5:1 SWR doesn't bother me much. I
only care how much I give up in transmission line losses to that number.
On 80-~20 it's not enough to excite me, but on 10, I get a little
careful. Unless you have a really long run the RG-8 type low loss cables
make the discussion more academic than worrisome, and I mean like the
Belden 9913, Times Wire LMR-400, or equal. I do not equate antenna
resonance with an SWR of 1:1, either. There are only a few times an
antenna is resonant and it reflects 50 Ohms.
If you have the room and can put up only one antenna, a dipole for the
lowest operating frequency is good. Just, get it as high as you can, on
both ends. Anything else you do is containing the SWR variations over
the bands such that you can deal with it. If you do go with a center fed
antenna, open wire is really good as it has the least loss of any other
feed line. However, you will need a balun, a good current balun, as
today's radios want to be connected to coax cable.
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