6 Meter long wire matching
Tom Azlin, N4ZPT
n4zpt at cox.net
Sat Jan 5 20:59:59 CST 2008
Hi Bob,
Well, with a half wave the quarter wave point is 72 ohms. With a
resonate antenna it should be resistive no matter where you check. When
you stack more half waves the end effect shifts the minimum impedance
point but there should be a place where it is back to 72 ohms or such.
Ground effects would I thought reduce the impedance. Sounds like a
question for Mike Toia, K3MV, our local antenna engineer.
I guess we can just make them and then try it both ways. Is there a way
in the model so search for the low impedance point and see what it turns
out to be?
Mike - we are looking at making a long 6 meter antenna of perhaps 6 wave
lengths or more. And feed it from a good point. I was thinking that a
quarter wave in it would be back to a low impedance not much different
than feeding a half wave in the center. But modeling it gave 400 ohms or
so. We are operating monoband. What would you say here?
Thanks and 73, Tom Azlin n4zpt
Bob Bruninga wrote:
>> If you are using it only on 6 meters then you do not need to get an
>> impeadance transformer. Just hook coax directly to the wire a
>> quarter wave from the end away from where you want the gain.
>
> But when I modeled it on EZNEC, I get about 400 ohms at that point.
> Yes, it is mostly resistive, but it is around 400 ohms. Hence, I
> don't need a tuner or matching system other than just an impedance
> transformation that I can simply do with 1/4 wave of about 140 ohm
> line.
>
> So to get 140 ohm line, I am trying to remember the trick o using two
> lengths of 70 ohm line... but dont remember what to do with the
> shields.
>
> Bob, Wb4APR
>
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