RE: ATU efficiency and the Elecraft T1

Posted by Don Wilhelm-3 on Aug 09, 2005; 3:03am
URL: http://elecraft.85.s1.nabble.com/Re-Elecrafts-T-1-tp381070p381082.html

Darrell,

It all depends on the electrical length to the feedline at the frequency of
operation.  Sorry, but no better answer exists.

If your antenna is end fed (like the example of an end fed dipole), the
impdance at the antenna feedpoint will be high, but if the feedline is an
odd multiple of a 1/4 wave (elecrtical), the impedance presented to the
shack loaction should be low.  At other lengths, the impedance at the input
to the feedline will be high or low or something in between and will depend
on the length of the feedline.  Whether it is better to use a 1:1 balun or a
4:1 balun depends on the answer to these questions.

73,
Don W3FPR

> -----Original Message-----
> > L. B. Cebik, W4RNL, explored the "im balance" of the end fed
> Zepp antenna,
> > a half wave with open wire feed where one side of the wire connects to
> > nothing, and the other to the antenna end element.
> >
> > That would seem to be the extreme case of current imbalance but he found
> > typically, there is only 10 per cent less current in one
> conductor at the
> > rig end, than the other.  The line seems to divide the power available,
> > rather than one wire being a true zero current.
> >
> > This was done for a floating system, or a closed system, ie dipole in
> > space, no other ground.  That would pretty well approach the floating
> > system you have used on rock.
> >
>
> So how would the Elecraft BL1 Balun do with the End-Fed Zepp?
> Depending on the
> ground losses, the impedance could be 5000 ohms or so. Would the 4:1
> transformation ratio still hold true? What would the efficiency
> of the balun
> be? Would 100 watts from a K2/100 cause saturation of the balun core?
>
> --
> Darrell Bellerive

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