On Sat, 29 Jan 2005 02:56:46 -0500, Doug Faunt N6TQS +1-510-655-8604
wrote:

Hi All,
I've built a 30M Jpole using dimensions from the Jpole calculator in
Hamcalc and using 300 ohm twin lead for the matching section.

It seems to resonate about right, but the SWR is 2.2. I'm using an
Autek RF-1 analyser, and want to know if there's any way to determine
what changes to make to get a lower SWR? I don't have a lot of the
twinlead left, and don't have enough time to get more, so cut-and-try
isn't the best solution.

73, doug

Thee are two things you have to take into account:
1. tuning your radiator to resonance (reactance = 0 on Autek)
2. matching to your feedline.

What does your Autek say?

If the reactance is capacitive, lengthen the 1/2 lambda radiator. If it is
inductive, shorten it.

Now that the antenna resonates, you have to match it. The antenna handbook
details calculating the proper length of 75 ohm coax to transform
impedances from 50 to something else. Your Autek will tell you what the
"something else" is.

Why a J-Pole?

Would it not be easier to simply string a vertical dipole? A J-Pole is
merely an end fed vertical dipole with a tapped shorted 1/4 lambda
matching section.