Edward Feustel wrote in
:

I have a centerfed 220 foot dipole I am using on all bands from 160 -
10 meters. It is between 40 and 50 feet above silt soil and is fed
with W7FG open wire (600 ohm?) Currently I am using a 4:1 balun at the
output of the antenna tuner to transform impedances to an L-Network
that allows the transmitter to see a close match at 50 ohms.

I am interested in opinions on whether it would be better for me
to use a 450 or 600 ohm balun that might more closely match the
transmission line (in practice).

I believe that with the reactances involved, so theoretically it might
not make much difference. Anyone with actual actual experience
who would like to render an opinion?
Thanks,
Ed


Ed, you could come to an opinion on this if you treat the system as
comprising lumped constant components.

But, it isn't simply that.

If you were to use a common mode choke, and that is probably the best
choice, eg W2DU style balun, the balun acts on the common mode Zo rather
than the differential mode Zo ( the 450 / 600 you are discussing), so I
as why is the differential mode Zo so important in selecting the balun.

I know there are rules of thumb (ROT) about the parameters of the balun
wrt the differential Zo.

It is true that such a balun does contain a short length of transmission
line, and that means some amount of impedance transformation for loads
other than Zo, but IMHO it is not very significant in your tuned feeders
multi band dipole.

Obtaining an adequate choking impedance is probably a more important
issue, but people are usually more concerned about the correct Zo for the
balun.

Owen