[Antennas] J-pole gain

Sat Jun 30 11:07:32 EDT 2007

Tim,
 He is correct. A lamba/4 vertical over perfect ground has a directivity of about 5dBi. The J-pole, being effectively an end fed lambda/2 vertical dipole, with its center lambda/2 above ground, behaves as two stacked dipoles with a center-to-center spacing of lambda when the image in the ground is taken into account, and has a gain of 8.3 dBi.
 However, this is for a conventional J-pole with a single parasitic element at its base. It is directional, with about 4dB of directionality. The driecionality may be removed by using two parasitic elements at the base, equally spaced on opposite sides of the driven element. For this arrangement, the gain drops to 7.8 dBi.
Hope this helps
73
Brian KF2YN