On Thu, 25 Jun 2009 08:34:00 -0700 (PDT), dykesc
wrote:

I'm going to 450 ohm window line to my OCF Dipole. Obviously, as
confirmed by EZNEC, without some kind of choking action at the
feedpoint, my feedline will be radiating. What kind of 1:1 choke could
I use on the 450 ohm line at the antenna feedpoint? I could build a
1:1 choke with the right toroid but not sure if I can maintain the 450
ohm line Z0 through the choke.

No, you cannot, but is that important? Select a product that works
and connect the line to it, and the antenna to the other side. Of
course "works" means: offers sufficient Z in relation to the load and
the line. "Sufficient" means: 10 times Z.

Going further, what is the point of 450 Ohm (sic) Window line in this
application anyway? An OCF would only demand a 200 - 300 Ohm line
depending on where the off-center is off center.

Given there are an infinite off centers to every center, that makes
for a lot variation in drive point Z. Have you selected the optimum,
or just going for an ad hoc design? Given your 450 Ohm desire for an
antenna reputed to be 200 Ohms, it would seem you are guessing.

As you report you have EZNEC, the solution is at hand. Put up the
longest wire you can run. Place the source at the center of 101
segments. Set the alternative SWR source Z to 100 Ohms. Run a full
sweep from 3 to 30 MHz at 10 kHz increments. On a separate chart of
about 10 columns, make notes of each dip in SWR (about 4) in columns
that are spaced equal to the dip's relation to the full 3-30 sweep.
Now move the source 5% and repeat the steps. Keep moving the source
towards the end by 5% steps, again repeating the steps.

I've done this and know where the "best" offset is, but telling would
cheat you of your investment in EZNEC.

73's
Richard Clark, KB7QHC