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JPOLE PROJECT
by Alan Homes KG4WOA |  |
The J-Pole antenna is a basic antenna, suitable for base or portable use on 2 meters. I wanted to build a one-half inch copper pipe antenna for a home base station, and found virtually an endless source of information on the internet. Most of the sites with plans included a calculator for determining pipe lengths.
Combining ideas from the following sources allowed me to produce a good quality antenna, with excellent SWR readings.
www.qsl.net/wrav
www.packetradio.com/j-poles-unlimited.html
www.martechsys.com/kb9vbr/jpole.htm
www.tcars.org/elmer/jpole.html
www.main.org/wcares/projects/j-pole.html
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Materials needed:
1 ten foot section of ½ inch copper pipe.
2 end caps
1 tee
1 90Ί elbow
1 SO-239 chassis connector.
Radio Shack # 278-201
Ham Radio Outlet #407TS
1 ½ inch pipe strap
1 ½ to 5/8 hose clamp (auto parts store)
1 #6-32 X 1 inch brass bolt and nut
12 gauge solid copper wire
I found it a good idea to buy several of the bolts/nuts and straps.
You can cut the pipe into proper lengths in the hardware store parking lot. This saves aggravation when trying to fit a ten foot pipe into a 6 foot trunk.
Tools required:
Propane torch
Rosin core solder
Flux (I use brush on)
Measuring tape
Sandpaper for cleaning ends of pipe (100 grit)
Pipe cutter (hacksaw will suffice, pipe cutter works much better)
Patience
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Pipe cut to length, 58, 19, 11 and 2.
90Ί elbow, Tee, and end caps
SO-239 chassis connector
Solder, flux, flux brush
Sandpaper, torch and sparker.
Not shown are the pipe strap,
6-32 bolt/nut and
worm clamp.
They were an afterthought. | Sanding the ends of each pipe.
This is important, for good bonding.
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| Brushing on the Flux | The "tee" slides on. |
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| Applying heat and solder | Finished joints, ready for 90 degree elbow |
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Pipe is allowed to cool, then laid flat
on bench. This allows elbow to align
with pipe. You may have to fiddle with
it. | This is how it should look from above.
Solder this on, then attach other pipe. |
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I inserted pipe into elbow and soldered it
while laying flat on bench. This ensures
both will be parallel with each other.
Yes, the bench does get hot. | This is how the SO-239 looks attached
to the long section of pipe. The ½ inch
clamp will be tight. Note the 12 gauge
wire soldered into the S0-239 stub. |
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The hose clamp secures the wire. Do not
tighten fully, allow a little slack for checking
SWR, sliding the clamps up and down
slightly allows for fine adjustment. | Create a choke by winding three or four
turns of coax below your feed point.
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WHAT I LEARNED DURING THIS PROJECT
My original idea was to solder the S0-239 chassis connector and feed wire directly to the antenna masts. I used the hose clamp method for the wire and small plastic wire ties for the connector. The SWR was perfect across the band. I then soldered the connector and wire, re-checked SWR, they had skyrocketed. Why, I do not know. The hose clamp and pipe clamp method seem to work best. Just leave a small amount of slack when adjusting, then tighten up.
I do remember reading about coiling the coax below your feed point. I originally forgot to do this. While out in the field, with a SWR meter, I noticed the coax was looped around in a natural circle. I straightened it out, and happened to look down at the meter. Realizing my error, I immediately remembered what to do, and created the loop. A big difference in SWR readings.
Secure your coax as shown in the last illustration.
Good soldering requires the flame to be approximately one inch from your pipe, and centered.
I used an electric soldering iron for the 12 gauge wire/chassis connector stub.
Buy your pipe in 10 foot sections, its cheaper. If you plan on building a few antennas, purchase the fittings by the bag, its
.cheaper. |
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