J_Pole Trials and Tribulations
"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.
jimbo - AJ7IM
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