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Old January 17th 06, 01:20 AM posted to rec.radio.amateur.antenna
jimg
 
Posts: n/a
Default Dipole and Ladder Line Matching

jimg wrote:

ok, got me. to be accurate, eznec says the feedpoint Z is
32-j68.5...the apex is only 60' in the sky so the feedpoint impedance
is not too high. so that's where the 12:1 roughly came from (i was
playng with the height above ground).

so the question remains, ppl really run a very high swr at the
feedpoint..is there any advantage to matching at both point? i.e.
a fixed balanced impedance transformer up there at the feedpoint, and
then, of course, a tuner down here.



jimg wrote:
Hi. I've heard and read some about ladder line and dipoles.
So what is the basic configuration look like? My impression is
the set-up starts with either a balanced tuner with 400 ohm output
or a 50 ohm tuner with a 4:1 balun to the 440ohm ladder line. The
ladder line then runs to the dipole and that's pretty much about it.

So my EZNEC on my future backyard Vee shows about 60ohm which is about
a 12:1 mismatch at the antenna feedpoint! So do I have something wrong
in the basic config? Or do you all put a balanced impedance
transformer up at the antenna feedpoint?


Here's what I did and it works very well.

http://www.qsl.net/w5dxp/notuner.htm

An SWR of 12:1 on ladder-line is acceptable but where did that value
come from? 440/60 is 7.3:1. And your 440 ohm ladder-line (Wireman #554)
is probably closer to 360 ohms.


jimg
Oregon
USA