[Antennas] J-poles

Thu Aug 12 21:50:27 EDT 2004

At 05:27 PM 2004年08月12日, Cletus W Whitaker wrote:
>With due respect to all concerned, I don't think
>the author give any consideration that an antenna
>such as an end-fed 1/2 wave can be voltage fed,
>not current fed. The Zepplin antenna was a 1/2
>wave wire fed with a 1/4 wave, or odd multiple,
>open wire transmission line. The transmission
>line didn't have to be 1/4 wave, but it had minimum
>voltage at the transmitter if it did. I make J-Poles
>that don't use the feed coax as a radiator because
>the overall antenna is designed like a Zepp. The
>coax shield connects at the bottom, not some place
>up one side.

W8JI considered that case in the section titled: "The Next Zepp Step"
http://www.w8ji.com/end-fed_vertical_j-pole_and_horizontal_zepp.htm
Even voltage fed antennas have some current flowing into the fed end, 
otherwise there wouldn't be any power transferred. (Just as current fed 
antennas have some voltage at the feedpoint.)
The bottom connection was exactly what Tom analyzed. Regardless of where 
you connect the feed coax to a J-pole or end-fed Zepp, it can radiate since 
current can flow on the shield.
73, Terry