> Couple of questions. It looks like between dipoles #2 and #3 it is
> 31". Is this going to be the same if it is setup for omni?
It may change a bit depending on how much slack there is in the harness. In
reality, there will be little change in gain (on the horizon) if the spacing
is varied slightly, but generally speaking, it's best to keep them spaced
evenly (an inch one way or another isn't going to matter). The minor lobes
above and below the main lobe will move around a bit as the spacing is
changed, but for a DB408, the elevation pattern is fat enough that minor
lobe nulls probably aren't a big concern unless you're HAAT is way above
very close-in users.
I've ordered DB-408's set up for both omni and elliptial, and the bay
spacing wasn't consistant between the two.
Because the dipoles are all oriented vertically, there is little
element-to-element coupling between the vertically-aligned elements, so as
long as the spacing remains relatively wide, you won't see any appreciable
change in feedpoint Z. In contrast, if the elements were horizontally or
circularly polarized, mutual coupling between elements would tend to be
greater, and changes in feedpoint Z would be likely as you varied the
spacing between the elements.
> Also...I am using a longer pipe than the normal pipe for the db408.
> Will it matter if it is not 11 3/16" from the top?
>From an electrical performance standpoint, the mast pipe should extend above
the top-most element. Having a lot of excess pipe (2, 3, 4 feet or
whateveR) above the top element won't alter the electrical performance, but
adds more lightning protection.
--- Jeff WN3A
