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THE 2 METER SLIM
JIM
COPPER TUBING
ANTENNA PROJECT
BY
RICHARD
KE5FXU
SK
(Updated
1-16-2012)
(Credit for the original design goes to F.C. Judd,
G2BCX)
Get that signal lower to the ground for better
performance!
Why is the
Slim Jim so much more efficient than the popular 5/8 wave or other ground
plane antennas, despite the latters claimed 3dB over a
dipole?
The Slim Jim vertical angle of radiation is almost parallel to
ground so maximum radiation is where it is needed: straight out and in all
directions!
The
vertical angle from the Slim Jim is about 8 degrees, while the common
5/8th wave ground plane antenna is about 32 degrees. With all ground
planes, including those with radials a wavelength long, the vertical angle
radiation is tilted upwards at an angle of 30 degrees or more.
This
gives the Slim Jim a "gain" over a 5/8th wave of about 6dB when measured
parallel to the ground!
Presented below is the Copper Slim Jim
antenna project for 2 meters
built by a new ham....KE5FXU......RICHARD
BUSH for your enjoyment.
Congratulations
"Rich" on the new ticket and this fine Slim Jim antenna
project!....N4UJW
2 Meter Copper Slim Jim Antenna Project
By Richard Bush
KE5FXU
I have
been wanting a " Ham ticket " for a long, long time !!
I met Don
(N4UJW ) about a year ago, and he persuaded me to get very, very
interested in HAM RADIO, as a result, I received my Technician ticket and
call sign, KE5FXU, in September of 2005!!!!. WOW!
I visited Dons' web site (Hamuniverse.com ) and picked out the
2 Meter Slim Jim antenna project from the antenna project page and wanted
to build it from copper tubing. I wanted to have it finished to use
as a base antenna by the time I got my ticket !!
The bottom line is that the antenna works GREAT, except
for one thing......
I have too many trees !! They seem to
attenuate the distant repeater signals a bit. My antenna " farm" is
totally (including overhead) surrounded in all directions by a dense cover
of tree trunks, limbs and leaves in assorted sizes and a couple of curious
raccoons and a cat or two that helped in supervising the installation of
the antenna! (See picture below)
The trees were in full foliage when the antenna went up attached to
the upper end of a 20 foot section of PVC pipe.
Now that the leaves
are starting to fall with cooler weather setting in, I expect that the
distant 2 meter repeaters will be stronger on my brand new Icom IC-V8000.
I had a lot of trouble programming
it but that is another story!
Construction of
the 2 Meter Copper Slim Jim Antenna
(Slim Jim details here)
Completed antenna on left and shown standing in
front of standard size door
The construction is really simple.. If you can
sweat a copper joint, you will not have a problem ( some of you may need
help with reading a tape measure, using a tubing cutter, etc). The
dimensions are not that critical, except for the finished length ( 58 "
)..
MATERIAL LIST (ANTENNA
ELEMENTS)
Antenna elements are 1/2 inch copper
tube
I started with two sections of copper tubing 6' long
purchased from Lowe's. You can get all of the sections for the
Copper Slim Jim antenna from these with very little waste.
long side 56 1/2 " -
1 each
1/2 wave 36 1/4 " - 1 each
1/4 wave 18 1/4 "
-1 each
1 3/4 "
sections -2 each ( these two pieces determine the width
of the antenna, 2" center to center, one at the top and one at the bottom
of the slimjim )
90 degree elbows - 4 each
End
caps - 2 each (Install on the tubing
ends at the air gap to keep out water)
FINAL lengths should be near or as close as possible to 58
inches long, end to end, with about 2 inch spacing center to center
between both vertical elements at top and bottom. Insulated separators
made from wood or other material are used between elements at top and
bottom for mechanical stability. See completed antenna elsewhere on
page.
The SWR
"Adjuster"
Adjuster mounted on Slim Jim
Editors note......this is a very novel
idea from Richard, KE5FXU, for adjusting the swr during the final
stage of tuning the copper slim jim antenna. It can be either left on the
antenna permanently or just used to find the attachment points of the coax
for direct connection (solder) if you decide not to use it. You just
attach your coax to the wing nuts and slide up and
down!
SWR ADJUSTER PARTS LIST:
wood- 3/8" x 1" x 4" - 2 each
spacer 1" x 1" sq. - 1 each
carriage bolts: (
galv. or plated ) weather proof !!
(Flatten
heads with file for better contact)
1/4"x 1"
bolts
- 2 each ( these 2 bolts come up thru the bottom of the top piece of
wood, all of the wing nuts are on top. )
1/4" x 1 3/4" bolt - 1
each ( center hole )
1/4" flat
washers - 3 each
1/4" wing
nuts
- 3 each
Total
cost of antenna around $13.00 U.S as of November, 2005
(no charge for
labor...HEE HEE)
The adjuster is simple to make. It is two pieces of wood with a 1
inch square spacer in the middle. (See picture) I used some scrap oak
flooring. Drill a 1/4 inch hole in the center of all three pieces. Glue
the spacer in the center of the bottom piece. In the top piece, drill two
1/4 inch holes that coincide with the center of each piece of copper (
with the long element on the left and the 1/4 wave element on the right ).
The 1/4 wave side is at the bottom of the antenna.....The coax connects to
the adjuster bolts, center wire on the left, shield on the right.....
Approximately 3 to 4" up from the bottom of antenna. The adjuster is moved
up and down to find lowest swr point during tuning. Make sure you
tighten the wing nuts each time you take an swr measurement and then
loosen and move in either direction if more adjustment is needed. (Use LOW
POWER)
If you
take a good look at the picture of the adjuster, you can see the marks on
the copper tubing where the coax could be soldered directly to the tubing.
I decided to leave the adjuster on as a permanent fixture of the
copper slim jim but you don't have to if you solder the coax connections
directly to the antenna . This adjuster really helps in tuning this
antenna and could be used on other antenna projects such as J poles or
similar antennas. The final, installed swr measurements using 50 feet of
Rg8 coax feed line (taken with an MFJ 259b) were as follows:
Final installed SWR
readings with top of antenna 20 feet above
ground:
144mhz
1.6
145mhz
1.4
146mhz
1.2
147mhz
1.1
148mhz 1.1
These measurements indicate that
the overall length is a bit short with swr lower at the higher end of the
band but the length was not changed. The antenna length could be altered a
bit (longer) for a bit better performance in the mid band region by
closing the air gap slightly.. GOOD LUCK !!
Update - - Further
testing and design with an aluminum version with a 1 inch gap works well. Your results may differ
depending on your construction.
If you
decide to build this antenna, please let us know your results.
Any comparison results with any other 2 meter
antenna would be greatly appreciated.
Please send them to n4ujw at
hamuniverse.com
Additional input from other builders:
Alan, KE4NU reports that he built
a 450 ohm ladder line version seen
here
and that when compared
with a commercial built J Pole, there was an increase of 2 S units with
the Slim Jim.....Thanks Alan!
KI4SNW - Matt reports on the
Copper Slim Jim antenna he built with great sucess as follows:
73 Matt KI4SNW
See additional final installation picture below BY KE5FXU:
Proud builder and
Crew!
Antenna is located
between red and yellow arrows in picture above mounted on PVC pipe.
A
mounting suggestion is to use plastic or nylon wire ties that are UV
resistant or use your own method.
It is not
certain which of the characters in the picture is Richard!
Optional suspenders and T shirt were missing when the
picture was made so this makes identification more
difficult!
|
In Memory of my good
friend John R. (Richard) Bush Jr. |
Footnote by Don
Butler, N4UJW
I remember helping "Rich" get his Technician Class Ham
license on 9-12-2005. He was so excited after his third try and upon
passing the exam, he could hardly wait to get on the air. After installing
various antennas and getting them to work right, he finally started making
contacts on 2 meters and HF and he would call me every time he made a
new one............
Now he has made his final and greatest DX
contact! Rest in peace my dear frind! I will remember the good times we
had! Thanks for the opportunity of knowing you as you passed by me on your
destination in life!
Don
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