-.-. --.- wrote:
... what decide the feed point
modality (I or V) ??

1/4WL down from the tip is a current maximum point.
1/2WL down from the tip is a voltage maximum point.
3/4WL down from the tip is a current maximum point.
4/4WL down from the tip is a voltage maximum point.
5/4WL down from the tip is a current maximum point.

i.e., odd multiples of 1/4WL are current maximums.

i.e., even multiples of 1/4WL are voltage maximums.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com