> even if the harness is balanced it's only effective at the
> design freq so a freq change makes a phase shift and alters
> the tilt / transmission angle ?
>
Don't think of the feed system in terms of wavelength multiples - I'm
guessing that's where your train of thought is jumping the tracks.
Consider a two-element array. We'll ignore matching issues here to keep
things simple. At the antenna feedpoint is a tee, and from the tee there is
four feet of coax to each element. At some frequency (say, 150 MHz), the
total electrical length from feed to element is some fraction of a
wavelength; since I didn't specify the velocity factor of the coax I'm just
going to pull a number out of thin air here, so let's say that our five feet
of coax is 1.0 wavelength at 150 MHz.
Now let's add 10% to the frequency, making it 165 MHz. The cable length
from the tee to each element is now 1.1 wavelengths at the new frequency.
BUT, the *difference* in phase between the elements is still zero! It's the
difference in phase that causes the beamtilt, and since the elements are
still in phase, there is none.
It's no different than keeping the frequency the same but adding
identical-length extensions to each of the two feeder cables.
Did that make sense?
--- Jeff WN3A
