"jimbo" wrote in message
. ..
I have been trying to get an acceptable 2 meter antenna installed in
my attic. A J-Pole seemed to me the best solution for my attic space.
You may recall an earlier post where I discussed SWR on one of the
ladder line J-Poles I was working with. Well, I gave up on ladder line
and constructed a J-Pole from 1/2 inch copper tubing. I tuned it in my
basement work shop to give the best SWR and then took it up to the
attic. The following table shows the results.

Basement Attic

144 1.90 1.80
145 1.65 2.00
146 1.50 2.10
147 1.60 2.25
147.995 1.90 2.25

Actually, probably not that bad for a first attempt at copper tubing.
But, I didn't like the fact that SWR was above 2.0 in my attic and
that things changed between my basement shop and the attic. I guess
this design is influenced by objects close by.

So, somewhere in my surfing I came across the Arrow J-Pole. This is an
end fed, open stub commercial design that promises less that 1.5 SWR
across the band. Here are the results of my experiment with this antenna.

Basement Attic

144 1.10 1.22
145 1.18 1.10
146 1.25 1.20
147 1.30 1.32
147.995 1.40 1.42

Not 1.0 SWR but certainly met the promise. And the best thing about
this design is that near by objects don't seem to have an impact on
performance. If I built one of these designs and tuned it in my
basement shop, it should give the same results in the attic.

Anyway, just my subjective observations.



Not to detract from the other posters ... IMO they all made valid comments,
but I offer this:

As the builder of about 20 copper pipe j-poles, I discovered that I can get
a better final VSWR if I include a 100 pF (or so) cap in the side fed by the
coax center.

I had been attaching an SO-239-type bulkhead connector to the short side of
the J and running a piece of solid wire from the center pin over to the long
side of the J. I could get the VSWR to a dip near the middle of the band by
monkeying with the feed point and/or trimming the length but the lowest I
usually got was around 1.5 : 1. As soon as I used the cap in place of the
straight wire, I could get 1:1. It works for me ... your mileage may vary.

I built more j-poles for 2M than all the others combined and 20 is not a lot
of antennas. For some reason, the cap seems to help the 2M size more than
it helps the others, but these antennas are too few in number for scientific
judgements by this amateur plumber.

73,
John