Making a J Pole antenna for 2M and 70cm
I
plan to use my Baofeng UV82 for mobile and also base station for now.
Maybe eventually I will get something with more power. But for now its
my only radio.
So far I have a mobile antenna for my
vehicle and an extended whip for handheld use. But as a base station a j
pole antenna will fit the bill for better gain and range. I'll need one
for 2M and 70cm.... make them separate and mounted together for either
outdoor mounting or attic mounting (suspended from attic beams with a
hook) or floor mounted (with a pvc base).
Outdoor
mounting will be interesting.. My backyard is a bird haven and I don't
think it will be long before the little tiny creatures will find the end
of the pole for a landing spot.
The 2M vhf antenna
will wind up being ~ 60 inches in height. I saw someone who used a
copper union on the long run to break it down for portable use. It would
be nice to make it versatile for temporary and permanent locations.
Plans
for this one will be 1/4" copper tubing and elbows. One tee on the
bottom run to solder in a base extension that can be adapted to a PVC
base for portable operation or clamped to a wood 4"x4" upright 8 ft
high. Another possibility would be a chimney mount but not for two
antennas. I probably will save the chimney location for a discone for my
SDR radio.
The design for the antenna is calculated with:
You can find the handy calculator and diagram at
http://www.hamuniverse.com/jpole.html.
Note: the feed point may need small adjustments so don't do a final
soldering until the position is finalized. (Hose clamps will do fine for
evaluation. Although not critical its common to connect the center of
the coax to the main stub and the shield to the short stub.. Using a SO
239 connector will facilitate quick connect / disconnect.
Later I'll look into making a lightweight portable with 300 or 450 ohm ladder line.
