Paul,
Perhaps you can now explain how the radiation pattern changes on a single
center fed, 1/2 wave length simple dipole when the frequency is changed both
above and below the dipole resonant frequency, and how that relates to the
statements you have made below.
73 Allan Crites WA9ZZU
Paul Plack <[EMAIL PROTECTED]> wrote:
"No, parallel-fed antennas do NOT suffer uptilt/downtilt as
frequency is varied unless the harness was special-ordered for factory
downtilt. If the antenna wasn't ordered with downtilt, all of the elements are
fed in phase, and they will always be in phase regardless of frequency."
Jeff, the pattern depends on both phasing and spacing. As frequency drops,
the interelement phasing, expressed in degrees, remains the same, but the
spacing, expressed in degrees or wavelengths, drops. If you model a colinear
array of parallel-fed dipoles in an antenna software program, and don't scale
the dimensions as you scale the frequency, you'll see the main lobe shift up or
down, and "butterfly" lobes appear, as you get a few per cent off-frequency.
In an extreme case, a pair of vertical colinear dipoles fed in phase with
half-wave spacing has the familiar big lobe toward the horizon. As frequency
rises, the pattern degrades until, at a frequency of 2X, it becomes an end-fire
array, with most energy directed straight up and down. This happens with no
change in phasing or spacing.
73,
Paul, AE4KR
