At 8/25/2008 20:34, you wrote: >If you extend the dipoles further from the mast, you will loose the >capability to stagger the dipoles around the mast to obtain omni >coverage. Even with the close spaced dipoles there is a slight scaloping >of the vertical angle as you go around 360 degrees. The further out the >dipoles are placed, the more variation in the vertical angle you will see. > >Back when the FCC required an antenna pattern for licensing a repeater, I >put a DB-224 on a mast and ran it through an antenna range, and observed >the scaloping. From that time on I have always prefered to put all the >dipoles on the same side of the mast and accept the 3 dB offset in antenna >gain. The plot is perfectly circular, but the center is offset with the >aligned dipoles. Gain is only 3 dB off the back of the mast but is 9 dB >in the direction the dipoles are pointing. And there is no scaloping in >the vertical angle at all -
I tried configuring the dipoles of a UHF 4-pole for omni coverage at one site & noticed very poor performance. Modeling the antenna in NEC I noticed not only is the pattern scalloped, but the peak gain is lower than the nominal 6 dBd as well. Bob NO6B
