On Apr 5, 2:36*pm, wrote:
I always assumed having more 1/2 elements in a collinear was best,
because that obviously raises gain and lowers angle. So from that
point of view, I was thinking that it would actually be better to use
a low VF coax, since that would give you shorter length elements, thus
being able to fit more elements in a shorter space. But I've also read
that having the element lengths closer to actual 1/2 length (longer)
is actually more efficient than having more elements at a shorter (low
VF) length. Just wondering what people's opinion is on this... So lets
say you have a choice between using the insulated center conductor of
a VF 78 coax through brass tube outer elements and having room for a
few extra elements in a given length, verses using just an insulated
wire that has a 99 VF through brass tube outer elements, thereby
allowing slightly less elements because they're longer, but the
elements you do have are closer to actual 1/2 length. Which would be
best? And this is basically various UHF bands we're talking about.

Thanks for any opinions,

Dave

So, why don't you do some modelling and see? I predict (having done
it myself) that you'll discover that the gain is pretty close to
proportional to length, independent of how many sections are used, at
least for practical velocity factors. In fact, you can optimize the
gain a bit by picking the VF, but it's not a big deal. What's
important here is how the mutual impedances among the elements affects
the current distribution on the elements, NOT how many elements you
have. Ideally, you'll end up with something close to the same
current, in-phase, at the center of each element; what you're liable
to see in a long antenna (say 10 elements) with moderate or low VF is
that one element out near each end will have a much lower current than
the rest. The effect of that on the pattern is probably less than
you'd have guessed.

The other thing that the free-space length of the elements will affect
is the feedpoint impedance. I'd suggest, again, that you model it to
make sure the net impedance of the paralleled feedpoints is something
you don't mind matching to.

Cheers,
Tom