| 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.|
1 ten foot section of ½ inch copper pipe.
2 end caps
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)
Sandpaper for cleaning ends of pipe (100 grit)
Pipe cutter (hacksaw will suffice, pipe cutter works much better)
|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
They were an afterthought.
|Sanding the ends of each pipe.|
This is important, for good bonding.
|Brushing on the Flux||The "tee" slides on.|
|Applying heat and solder||Finished joints, ready for 90 degree elbow|
|Pipe is allowed to cool, then laid flat|
on bench. This allows elbow to align
with pipe. You may have to fiddle with
|This is how it should look from above.|
Solder this on, then attach other pipe.
|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.
|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.
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