On Mar 17, 5:36*pm, (Dave Platt) wrote:
In article ,
Owen Duffy wrote:

A well executed ground plane antenna is an antenna that a person with
little knowledge and experience can implement with a high level of
confidence that it is reasonably efficient and effective.

That would certainly be another workable alternative for this
situation. *An SO-239, a few feet of 10-gauge solid wire, and a bit of
soldering, and you end up with a ground-plane antenna with a hanging
loop at the top, two or four ground radials drooping at around a
45-degree angle, and a near-ideal match to 50-ohm coax. *Cheap and
quick to make. *Stick a ferrite or two on the feedline just below it,
and feedline radiation shouldn't be a problem. *If I recall correctly,
this very design appeared in the "quick tips" freebie blurb I got from
the ARRL after I first got my ticket.

That is my choice for a vertical antenna hung from rafters.
I've got one in my attic. Quarter wave ground plane with
8 radials. Hung from the rafters with fishing line. I'm lucky
that my roof is fairly non conductive. All the ducts etc are
well below the antenna. I've never really like J poles for all
the reasons already mentioned. The radiator is 19 inches,
and ditto for the radials, except being as they slope at about
a 45 degree angle, they require less height than if the lower
half of the antenna went straight down from the feed point.

BTW, if you model them, the usual difference between a
1/4 wave GP and a 1/2 wave vertical usually amounts to
about .3 db... Not enough to worry about, and not enough
to make using the taller antenna really worth the extra trouble.
Not to mention the GP is much easier to decouple from the
line. And decoupling from the line is much more critical than
any extra gain from a longer radiator when used for VHF/UHF
and the very low angles most local contacts will use.
In many cases, the GP will outperform the J pole due to it's
better decoupled feed line.