"Cecil Moore" wrote in message
...
Doug Faunt N6TQS +1-510-655-8604 wrote:
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.

Probably not a J-pole shorted at the bottom but a J-pole
(Zepp) open at the bottom? The trouble with a Zepp is
there are no adjustments except length. With a J-pole
shorted at the bottom, you move the feedpoint until you
find the 50 ohm point. With the open ended J-pole (Zepp)
the 1/4WL bottom section is a fixed transformer.

Your feedpoint impedance is probably 110 ohms (don't think
it would be 23 ohms but it might be). Installing a 1/4WL
piece of 75 ohm coax between the feedpoint and your 50 ohm
coax should give you a near perfect SWR. For a piece of 75
ohm coax with VF of 0.66 (RG-11) that would be about 12.7
inches.
--
73, Cecil http://www.qsl.net/w5dxp


Hey, Cecil -

Did you slip a digit or two? 1/4WL at 30 meters with .66 V is just shy of 5
meters, no? I get about 16 feet.

John
KD5YI