[TenTec] The OCFD Mystique

Wade Staggs tvman1954 at gmail.com
Tue Sep 22 16:49:14 EDT 2015

*Once again I walk forward with my Asbestos Suit on hi .. hi .. In the QST
Article linked below, modeled on a 66 foot dipole. The SWR and Loss Figures
comparing Ladder Line ( Windowed Line ) and Coax is Drastically Different.
I know that the Antennas are different Beasts in many ways. And also that
the SWR Figures should be lower on an OCF Antenna. We are also very aware
that Ladder Line can't be used on an OCF Antenna because it is an
Unbalanced Antenna. But .... if you are going to need a Tuner anyway to
cover the Full Bands? Why do folks even bother with OCF Antennas? Just take
a quick look at the Gain an 130 foot dipole has on 20 Meters using Ladder
Line. Sure there are lots of Major and Minor Lobes, but the gain in the
Major Lobes is Outstanding. Plus you can run QRO without having enough RF
in the Shack to cause major problems. Hey guys, just asking here. There are
many people here that are Much smarter than me. You never learn unless you
ask the questions.... Someday when we can afford a Faraday Cage.... I would
like to play with OCF Antennas again .. hi ... hi ..*

           *So ... we sit here with the 1% Silvadene Cream and Asbestos
Underwear on. Please, be kind fellas This is an honest question because I
want to learn something.*
*                               73 from Wade/KJ4WS*

On Tue, Sep 22, 2015 at 12:35 PM, Barry LaZar <k3ndm at comcast.net> wrote:

> Fellas,
>     There is nothing magic about an OCFD. It just a variant of the Windom
> that was invented, I believe, in the 1920's. It's nothing more than a
> dipole fed off center so that when you use it on even multiples of a 1/2
> wave the impedance is either 50 Ohms or in the region of what your tuner
> can handle. If you can get it up 35 or more feet, it does make for a pretty
> good all around antenna. I have a variant called a Carolina Windom. It's up
> about 40 feet and I've worked DXCC, mixed CW, and phone. I've also gotten
> my WAS using it and 100 Watts.
>     The issue of SWR is a red herring. So long as you can tune the
> "system" such that your rig can accept what the tuner gives it, that is
> really all that matters. Yes, there are losses associated with high SWR,
> but if you use low loss transmission line, the additional loss due to high
> SWR can be pretty trivial, a 1db or so, depending on SWR and band being
> worked. On 10 meters my system losses total around 2 db which includes
> everything behind the tuner.
>     One thing that must be remembered is that the transmission line from
> the antenna to the station can be an impedance transformer if the SWR is
> greater than 1:1. What this means is that what you measure at the station
> may not be reflective of what the antenna is reflecting. So, some of the
> comments about this antenna works well over all but this band or another
> may not be accurate unless the effects of the length of the transmission
> line is included.
>     Bottom line from here is put up 66' or 132' of wire. Feed it ~ 1/3 of
> the way from an end. Use a 4:1 current balun if you don't want the feed
> line to radiate or voltage balun if you do. And, if you force the feed line
> to radiate, put a good RF choke about 15 or so feet down from the antenna
> feed point point, load it up, and start working the world. Just remember to
> use a good low loss coax like Belden 9913 or Times Wire LMR-400.
> 73,
> Barry
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*Living one day at a time with Jesus as my Savior. But, still having Fun.*

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