The 450 OHM Ladder Line Slim Jim
Antenna
By KE4NU - Alan Wilson,
Victor, MT
Want to homebrew an antenna for 2M? Want
something that actually works well? Want to get it up and running in an
hour or less? Enter the slim jim variation on the jpole.
After
researching the internet for easy antennas to build I came across an
article or two referring to a slim
jim antenna. Unfortunately, they were constructed out of copper
tubing or aluminum tubing which was too expensive and I didn't have any
laying around the shop. I also saw one using tv twin lead. Well, I didn't
have that either but I did have quite a bit of 450 ladder line laying
around. So, I decided to adapt the tv twinlead project to mine using ladder
line.
Construction (Refer to
drawing)
1. Measure out and cut about 59 or 60
inches of ladder line.
2. Strip both ends (top and bottom) about
an 1/2 to 3/4 inch and bend each toward the center so they will
overlap each other.
3. After you overlap the wire, measure the
entire length of the antenna. Your shooting for 58 inches total length
after stripping and overlapping the wires.
4. After achieving your
58 inches (give or take a half inch), solder both ends.
5.
Determine which end has the solid plastic closest to end and put a hole
through it so you'll have some way of hanging the antenna. (cable
tie)
6. On the opposite end (bottom end), measure up 19 inches from
the actual bottom (where wires are overlapped), and cut out a 1 inch gap
of 1 wire from one side only leaving the gap. You should end up with a
very thin slim rectangle from top to bottom with a 1 inch gap starting at
19 inchs up from the bottom on one side only.
7. Have an rg58 or
rg8x pigtail made with a pl259 on one end and shield and center wire
tinned with solder on the other end.
8. Measure up about 4 inches
from the bottom and remove the insulation from each side of the Slim Jim
antenna using the 4 inch measurement as your center point and remove
the insulation about 2 inches up and down from the 4 inch mark to
give you access to the conductors on each side of the antenna for swr
tuning.
9. Connect center conductor to the long side
and shield to short side in a temporary fashion. (I used crimp connectors
bent on the end of the pigtail which would connect around the each wire of
the antenna for testing).
10. Check your swr with an inline meter
or built in to your radio. I used the former (inline swr meter), with
an ht. Slide the pigtail up or down for your best swr and solder in
place.
11. Using 2 or 3 plastic cable ties, wrap them around the
antenna and pigtail so they will be parallel and snug and to reduce
strain on the soldered connection.
Your done, hang it and
talk!
Testing
I used a commercial jpole to compare the 450
ohm slim jim with. I hung each antenna on a hook using a plastic cable tie
at 10 ft using same length and type feed line and exciter at same power
level.
I could hear normally marginal signals an
average of 2 S units stronger on the slim jim and I could work into
repeaters that I could barely hear on the jpole.
Conclusion: I don't care what certain people publish
about the slim jim not being any better than a standard jpole. It DOES make a difference on transmit and
receive.
I used neither ferrite beads, nor a
homemade coaxial balun to keep the coax from radiating. You may use
either one you like if needed.
Now, go make something homemade.
Lemonade would be nice on a hot day!
73 Alan -
KE4NU ke4nu7@gmail.com
