I'm not quite clear what you are talking about, but the impedance seen
looking into the feedpoint of a 1/2-wave resonant dipole when the
feedpoint is at the centre, is a purely resistive 70 to 73 ohms.

As the feedpoint is moved away from the centre the impedance rapidly
increases (approximately proportional to the square of the offset) BUT
REMAINS PURELY RESISTIVE until, as the feedpoint nears the end of the
dipole, it rises to several thousand ohms, purely resistive.

This is the impedance which terminates the twin feedline. But if there
is a choke in the line at this point then the choke can be considered
to be a short length of line of the same length and Zo as is wound on
the choke.

The short length of line on the choke will then TRANSFORM the antenna
input impedance to a somwhat different value to terminate the line.
(For the purpose of calculating SWR on the line, and the line's input
impedance, etc.)

Now carry on from there. ;o)
----
Reg, G4FGQ


"Chuck Olson" wrote in message
...

"larry" wrote in message
...
Greetings

A gentleman on another group.. is telling me that he wants to put
up an
offset dipole antenna and feed it with a balum.. He is a new
amateur and I
can tell he does't have much antenna knowledge...

He is being advise to use an offset antenna wich in my mind isn't
the best
answer to his problem....

Does anyone know of a website that describes the offset antenna
better
than
I can....

Larry ve3fxq

Hi, Larry,

An off-center fed antenna doesn't necessarily produce unbalanced
feeder
currents - - just a different feeding impedance level, which he will
no
doubt take care of with a tuner or a 4:1 ratio in the balun if
single band
use is all he wants and he can find the right spot for the feeder.
Of course
the balun takes care of any unbalance that might be due to the
feeder
not making a 90 degree angle with the antenna. There's nothing wrong
with his idea.

I just typed it balum, too, so don't be concerned - - we all make
typos.

73, Chuck W6PKP

"Reg Edwards" wrote in message
...
I'm not quite clear what you are talking about, but the impedance seen
looking into the feedpoint of a 1/2-wave resonant dipole when the
feedpoint is at the centre, is a purely resistive 70 to 73 ohms.

As the feedpoint is moved away from the centre the impedance rapidly
increases (approximately proportional to the square of the offset) BUT
REMAINS PURELY RESISTIVE until, as the feedpoint nears the end of the
dipole, it rises to several thousand ohms, purely resistive.

This is the impedance which terminates the twin feedline. But if there
is a choke in the line at this point then the choke can be considered
to be a short length of line of the same length and Zo as is wound on
the choke.

The short length of line on the choke will then TRANSFORM the antenna
input impedance to a somwhat different value to terminate the line.
(For the purpose of calculating SWR on the line, and the line's input
impedance, etc.)

Now carry on from there. ;o)
----
Reg, G4FGQ

Thanks, Reg, for sharpening up the picture on off-center feeding of a wire
antenna. And thanks, Roy for bringing out the likelihood of asymmetrical
coupling to the off-center feedline and the difficulties that can result.

73, Chuck W6PKP