Ham Hints -
RFI Tips and
The 2 Meter 146mhz Slim Jim Antenna
With The 2 Meter (146mhz) Slim Jim Antenna Using Aluminum Tubing!
By N4UJW Hamuniverse.com
Well, here I go again! Not
wanting to be out done by myself and after having the temporary J
Pole To Slim Jim Conversion project lay down on the ground due to
some high winds we had, I decided to get with it on this 81 degree
day in January, 2006 (yes, 81 degrees in Texas in January! Won't
last long!)... and rebuild the old Slim Jim antenna conversion with aluminum tubing using half inch
diameter "junk" tubing that I found hiding from me.
The following instructions may help
you if you decide to try the Slim Jim antenna with aluminum tubing.
Refer to the Slim Jim Antenna Project for more details if needed.
I used half inch OD "junk" aluminum tubing cut to these final
NOTE: THE TOTAL LENGTH FROM TOP TO BOTTOM IS 57 1/2
You should end up with with a very, very elongated
rectangle with a space (air gap) between the shortest section and
the one above it of about 1 inch. (Again.....see pictures and refer
to the original Slim Jim antenna
tubing as follows:
>one section 57 1/2 inches
>one section 37 1/4 inches
>one section 19
1/4 inches (actually a bit shorter than this) 19.2 inches was used
in the original Slim Jim antenna project on the site using copper
tubing from the formulas on that page, but I rounded as close as
>2 sections of aluminum stock around 1/8 inch
thick and about 1/2 inch wide by about 2 1/2 inches long used as top
and bottom spacers "crossovers" to provide 2 inches between
elements. I did not have a good method for bending the tubing for
"one piece contruction" so I used the "crossovers" instead.
>assorted screws, nuts, lock washers and bolts. No I did
not use stainless steel....did not have!
non-conductive spacer from an old piece of plastic, PVC, etc. This
is used for support between short section and longest section about
5 inches down from the air gap. (See pictures below....it is a shade
of green/blue in the picture)
This spacer and the bottom
crossover of the Slim Jim antenna is used to mount the antenna to a
10 foot piece of PVC pipe at final installation by attaching self
tapping screws thru each one....see pictures.
section of non-conductive material between shortest section and the
top half. (dark color in picture) . This came from another antenna
"junk" pile. It is used only for support and an insulator, also to
keep the bottom and upper sections in line.
drilled holes suitable for the small bolts I had near both ends of
the longest section (57 1/2 inches), and one end of the shortest
section (19 1/4 inches) and one end of the section above the
shortest section. (37 1/4 inches)
Then I attached the "2 1/2
inch "crossover" sections used as spacers and crossovers at bottom
and top of Slim Jim using the bolts, lock washers and nuts.
I attached the air gap insulator/support between the lower and upper
The construction of the Aluminum Slim Jim antenna
was now finished except for mounting to the 10 foot PVC pipe,
checking and adjusting swr and having some fun with it.
Remember...this project was built from just scraps of this and that
found laying around my pile of "junk"....(junk is defined by the
XYL...it is gold to you and I)!
FINAL ADJUSTMENT WITH
I attached the Slim Jim antenna to
the PVC pipe using the bottom crossover section and the green/blue
spacer on the shortest section with self tapping screws. You may
want to use a different arrangement such as nylon ties along with
the screws or put bolts all the way thru the PVC for extra support.
The antenna ends up mounted against the upper most part of the PVC
pipe with the pipe in the center of both vertical elements.
To attach the coax to the antenna feed points, I used
standard adjustable hose clamps that would tighten down on the
shield and center conductor of the rg58 coax that I used. I suggest
you use stainless steel clamps....again....I did not have any.
The center conductor is attached to the LONGEST side of the
antenna under the hose clamp.
The shield is attached to the
SHORTEST section under the hose clamp. DO NOT tighten so as to cruch
the coax. ( My feedpoint connections were just a
temporary measure so I could easily slide them up and down for swr
tuning. ) They can be attached after tuning with screws,
nuts, bolts, etc.
I trimmed off enough of the black outer coax
covering exposing the shield about one inch and the center conductor
extended so they could be attached to the feedpoints.
I did not
measure. Cut coax so the shield and center conductor can be attached
underneath the clamps. I connected the coax center conductor first
and brought the rest at a 90 degree angle over to the shortest side
for it's attachment.
Tighten the clamps at around 4 1/2 inches
up from the bottom of the antenna. (This measurement was derived at
by my experimentation during tune up). Yours may be
The clamps at the feed point connections may have to
be adjusted up or down for the best match, hence, the reason for the
hose clamps. (The first attempt I made was with the feed at about 3
inches from the bottom.... and the antenna resonant point was way
out of the 2 meter band....about 138 mhz with an swr of around
3 to 1). This told me that the Slim Jim was way too long......after
adjusting the feed point closer to the air gap at 4 1/2 inches from
the bottom, I was in business!
These are the final swr readings
with the antenna up in it's final position....all of 10 feet above
the ground beside the house:
145mhz 1.1 Mfj 259b read x = 0 52
x = 0 52 ohms
x = 0 54 ohms
with a 98 percent match according to the Mfj 259b
All lengths of
the Slim Jim may be changed slightly either way depending on your
construction for better swr. You may not get that perfect 1:1
After I stood back and
marveled at my "new" Slim Jim, it dawned on me that the bottom
of the antenna was only about 8 inches from the metal roof flashing
under the shingles!
This was a NO NO according to all of the
Slim Jim articles I had researched on the Web.
distance should be no less than about 20 inches (1/4 wave) from ANY
metal in ANY direction!
I rechecked the swr, resonant points,
etc over the entire 2 meter band using the MFJ 259B, in case I had
made an error, (not a mistake), but the numbers were the same as
Now my curiosity came out showing it's ugly face, so I
managed to get the 10 foot piece of PVC pipe up higher so the bottom
of the antenna was at least 36 inches from ANY metal.....
Re-checked the readings using the Mfj 259b and to my
NO CHANGE AT ALL!
I suspect that the freespace
distance of 20 inches or more quoted in previous articles and
research on this antenna is used so the pattern will not distort up
or down from the "8 degree" angle of radiation from the ground. I
have not done further research or testing on the air to confirm this
but hope to in the future. If any of you out there wish to "model"
this antenna using different distances from surrounding metal....I
am open to your input.
An air wound choke
may be used at the base of the antenna to help prevent rf on the
feedline, creating difficulty with SWR readings, and help prevent
distorting the low angle pattern.. For 2 meters, the air choke coil
is about 4 turns of coax at 5 inches in diameter. Some builders use
it....some don't...I have not added one at this time but plan to in
the future to see if there is any effect on the
One note of further
information for you should you decide to build the Slim Jim.
During the period of time between this version and the
dismantling of the old Slim Jim, I decided to put it back up as a
Slim Jim antenna....take some S meter readings of area repeaters for
a reference and then re-convert the same antenna back to the old
readings of the same repeaters and compare them.
found that the Slim Jim could bring up several
of the same repeaters that the J Pole could not! No changes
were made between the two comparisons except the antennas!
tells me that the Slim Jim antenna has something going for
it.....try one and get something going for you.........HAVE FUN!
EXPERIMENT, EXPERIMENT, EXPERIMENT...
Notice the hollow insulator covering the air gap
the top of picture.