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

On Sun, 10 Aug 2008 11:24:54 -0400, Edward Feustel
wrote:

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?

Hi Ed,

You can easily dismiss the theory and take the quick step up to the
bar of experience - your own (who better?).

Does it match on the bands you prefer? Changing things will not
improve what is already acceptable.

Are you worried about what you cannot see? Loss? Ah! Then we
migrate into the world of the skeptical and theoretical where there
are probably questions you cannot answer - which questions require
data to give you specific solutions.

You ask one of these questions (by inference) yourself: 400 Ohms or
600 Ohms? You don't know, but it "could" make a difference. Here,
the "could" is a question of degree. Yes, on paper it is significant,
but in practice the listener of your signal would never note any
improvement if you invested effort, equipment, and time in finding the
answer and implementing a change to correct the "problem."

Let's examine what is significant. Would you like to eliminate 1dB of
loss (make that 1dB available to the listener)? Do you know what 1dB
looks like on an S-Meter? I would suppose so: about the thickness of
the needle. Would you invest $1000 to do that? Which is significant:
1. 1dB;
2. $1000.

Feel free to adjust both numbers to more closely conform to your
situation and expectations and respond in that context.

73's
Richard Clark, KB7QHC

Edward Feustel wrote:
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).

450/50 = 9:1, 600/50 = 12:1 - Is that what you are thinking?

On a transmission line with standing waves, the impedance seen
by the balun will NEVER be the Z0 of the transmission line.

Let's say you are using Z0=600 ohm feedline with an SWR of 20:1.
Let's say a current maximum point exists at the balun. The balun
will see an impedance of 600/20 = 30 ohms.

Do you want to use a 4:1 balun and take it down to 7.5 ohms? Why?
Do you want to use a 9:1 balun and take it down to 3.3 ohms? Why?
Do you want to use a 12:1 balun and take it down to 2.5 ohms? Why?

Do you want to use a 1:1 balun and leave it at 30 ohms?

When the impedance being encountered by the balun is unknown,
a lot of experts recommend a 1:1 current-choke-balun.
--
73, Cecil http://www.w5dxp.com

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

On Sun, 10 Aug 2008 11:32:24 -0500, Cecil Moore
wrote:

Edward Feustel wrote:
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).

450/50 = 9:1, 600/50 = 12:1 - Is that what you are thinking?

On a transmission line with standing waves, the impedance seen
by the balun will NEVER be the Z0 of the transmission line.

Let's say you are using Z0=600 ohm feedline with an SWR of 20:1.
Let's say a current maximum point exists at the balun. The balun
will see an impedance of 600/20 = 30 ohms.

Do you want to use a 4:1 balun and take it down to 7.5 ohms? Why?
Do you want to use a 9:1 balun and take it down to 3.3 ohms? Why?
Do you want to use a 12:1 balun and take it down to 2.5 ohms? Why?

Do you want to use a 1:1 balun and leave it at 30 ohms?

When the impedance being encountered by the balun is unknown,
a lot of experts recommend a 1:1 current-choke-balun.

Cecil,
I had never thought to try this!
I happen to have one that I was planning to use in a balanced tuner.
So I will try it and see how it wouks Practically.
Thanks.
Ed, N5EI