[TenTec] Thoughts about the "Windom" or OCF antenna

[Sinisa Hristov]

Stuart Rohre wrote:
 
> With all due respect to Sinisa, I would trust the L. B. Cebik modeling; as
> he uses all the available software and does extensive confidence and
> convergence testing of the model.


Hi,

as I see it, Mr Cebik did build his reputation
upon quality of his work, not the price of his tools.
Every mortal is error-prone, including me, you
and to some degree Mr Cebik.

In particular, Mr Cebik's modelling of "feedline radiation"
in the case of end-fed antennas is quite incomplete and unconclusive.
It leaves the reader with false impression that the only problem
here is "a little more radiation", which of course cannot be harmful.
But this is not true.

In his very inspirative "HF Antennas for all Locations"
Mr Moxon G6XN explains very convincingly why
end-fed antennas do not work in the advertised way,
although that does not prevent them working in some other ways,
depending on circumstances, and therefore unpredictable.


> Much simpler than trying the arduous current balun design route might be to
> just feed the "Windom" with parallel line and accept some modest vertical
> feeder radiation

As I explained a week ago on another reflector,
feedline radiation is NOT much of a problem.
Common mode currents have much more unpleasant consequences than
a bit of feedline radiation. Here's the article:
  http://lists.contesting.com/archives//html/Topband/2003-12/msg00291.html

This one may also be useful to some readers:
  http://lists.contesting.com/archives//html/Topband/2003-12/msg00188.html

It is misleading to state that one should accept the
unacceptable because "a bit of feedline radiation doesn't harm",
while ignoring a whole bunch of real problems.


> The problem I have with baluns mounted near the feedpoint is that weight
> issues for open span antennas are a real problem in the windy conditions
> we have twice a year.

Me too. I always recommend going InvV route with balun and feeder
supported by a mast, while antenna wire supports only itself.
Because of this average height can be increased easily.
If apex angle is made large enough, there is no performance loss
compared to the conventional shape, and there may be a small advantage
due to increased height of maximum current point.


> I always counsel the new antenna user to use a conventional dipole which can
> easily be hung as horizontal, or inverted Vee and is not complicated to
> feed.  The dipole can even be folded at the ends to be "Zee" in the
> horizontal plane, or have vertical hanging tails, or even put up as a part
> vertical, part horizontal, or sloping.

That's a very sound advice.


> There are so many ways to fit the half wave dipole into a space
> and have a convenient feedpoint, I am somewhat mystified what
> appeal the OCF has to the user.  It does not possess any
> property of radiation not also found with conventional half wave antennas.
> Nor does it have gain in its fundamental band application.

Again couldn't agree more.


> The only reason I hear most use them is that it places the feedpoint exactly above an
> existing window to the shack.

That was exactly my reason while living in an apartment building.
The feedpoint had to be within 10 ft of the anchor point, or there would
be no antenna. Feeding it with open wire resulted in so much RF in the
apartment that better solutions had to be sought. Eventually a suitable
balun was produced and many happy QSOs had. But this is hardly a route
to recommend.


> There is no harm in trying a simple parallel line fed OCF

Well, there is no harm in trying almost anything :-)

But having to rely on one's luck rather than on solid engineering
is not something I could recommend.


73,

Sinisa  YT1NT, VA3TTN