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How to Support the Portable Roll Up
 450 ohm Slim Jim Antenna for more permanent use outside
by N4UJW

Hang your roll up Slim Jim antenna supported from a mast to get it higher!



The 450 ohm roll up Slim Jim antenna designed as a dual bander for 2 meters and the 440 (70cm) band is extremely popular for portable operation on field days, for emergency use, camping, indoors and other times and locations. However it is not designed to be permanently mounted outside due to being made of 450 ohm ladder line which as you know is very flexible. This tends to limit its use if you want to mount it in a more permanent position outside on a support mast to get it up higher above the ground.

In this short article I will show you how I mounted mine made and sold by N9TAX outside, in a fixed "permanent" position on a metal mast a few feet above my roof line.

Yes, I said metal mast!
Although this was only meant as an experiment, after I completed it, it remained in place several months and performed as expected. Swr readings were very low on both the vhf and uhf ham bands. Coverage was remarkable being that the final installation was only about 11 or 12 feet up from the ground to the bottom of the antenna.

As you may also know, this antenna "family" does not like to be mounted next to any sort of conductive material like a metal mast, aluminum siding, near metal roofs, etc. There are many opinions as to whether or not to attach the Slim Jim on, very close, or inside PVC pipe of any kind so I came up with the method described in this article to get it outside and up higher.

I had seen an article on the N9TAX web site about making a "Bow" type support using PVC pipe for it but after looking at the design, I decided that it was just too time consuming for my needs and a bit tedious to make. N9TAX kindly offered the article for us to share with you.........You can see that article here.

My plan was to use straight PVC as the main support for the Slim Jim with the antenna hung between an upper and lower protruding horizontal section of the PVC but not touching it and then attach the PVC support which holds it to a metal mast.

Here is how I did it.

First lay your Slim Jim on flat ground stretched out to its full length. Weight it down so it does not move with whatever you have that is handy. Don't let it twist.

Then measure the total length of it from tip to end connector.

Mine was about 6 feet or so total length.

The idea now is to make yourself a single length of PVC that is LONGER than the antenna when it is stretched out and then include an additional length of PVC pipe to support it in a vertical position for mounting on a metal mast. This will be the vertical support section.

I selected a single length of PVC about 8 feet (eyeball length) or so using some spare ordinary white PVC 1 inch pipe from my "junk" pile.

I just guessed at the length I had and placed it beside the antenna, still stretched out. The total length of the antenna was shorter than the PVC by about 7 or 8 inches on each end. I was good to go with the rest of my plan! You will see how my plan unfolds as you read along.

Now with some more "junk" PVC that I had, I measured out 2 pieces of the same size PVC about 8 inches long to make the actual horizontal support arms that the antenna would be supported (suspended from) in a vertical position. Note that these 2 pieces are identical in diameter as the long vertical section mentioned above.

Now I attached (use either screws, bolts, or PVC cement), the 2 horizontal sections I had just cut using:

One 90 degree "elbow" at the top end of the long section.

One PVC "T" at the bottom of the long section.

(Note that the reason for the "T" at the bottom was to have an attachment point to extend a suitable length of PVC down to the metal mast which the whole affair would be mounted on.) See drawing below.

You should now have one long vertical length of PVC with 1 short horizontal length at the top and 1 short horizontal length at the bottom forming a sort of rectangle with a missing half similar to this:

 ]

Your next step will be to lay the Slim Jim at fairly equal distance from the 2 horizontal supports leaving about the same spacing between each end. The antenna must NOT BE TWISTED over the full length. Repeat, do not twist the Slim Jim antenna. It must be flat.

Now drill holes all the way through the outer ends of the horizontal PVC support arms. These holes will be the attachment points for the rope, cord, long UV resistant plastic ties, etc, that will connect to the antenna and will support it vertically and parallel to the long vertical length of PVC.

Your next step will be to select a section of the insulation at the top and bottom of the antenna ladder line near each end. This area on both ends of the antenna will be used for support rope attachments directly to the insulation.

Very important....DO NOT attach the support rope, etc to the bare wires connecting the 2  halfs of the antenna at either end. They may not be strong enough under wind load, ice weight, etc and will eventually break into if much pressure is applied!

Drill, cut or punch holes into the insulation that are large enough for the insulated (non-conductive) support rope you plan to use. Do not make the holes any larger than needed. You don't have much room to work with on the ends of the ladder line and remember that the insulation on the Slim Jim ends will be the "load" bearing part of the antenna.

Now using non-conductive rope, cord, heavy duty string, para cord, UV resistant plastic ties etc, thread it through the holes on the top and bottom of the antenna. Tie them securely.

Then attach the other ends to holes into the horizontal support sections at top and bottom.

Do not put much tension on the antenna when attaching the support rope. You just want the Slim Jim antenna to remain in a vertical position so it won't twist in the wind and it should remain vertical as much as possible.

Do not attach bottom support rope to the coax pig tail that comes with the antenna. Attach only to the insulation of the antenna. This will help prevent the coax feed point connections from coming disconnected from the antenna.

If all of this does not make sense to you..a picture is worth most all of these words.......

Roll up on mast
Slim Jim PVC support mounted on metal mast.

Additional notes of interest

Materials you will need:

 One length of PVC pipe
(diameter your choice) - about 10 feet total depending on your method of construction and how you mount it to the mast. Don't forget the horizontal lengths (2 each).
Note that the total length of PVC will be determined by your exact design. You may want to use a large diameter PVC at the mast mount section and reduce it down to the size for the vertical section. This section below the bottom "T" is the total load bearing area for the entire structure!

One 90 degree elbow
One PVC "T"
PVC cement, assorted nuts, bolts or screws as needed and support rope, cord, UV resistant nylon ties.

The diameter of the PVC that I used initially was 1 inch. I did not use cement, screws or bolts to attach the top elbow or the "T" at the bottom. I just press fitted everything together as tightly as possible and attached the antenna to the horizontal "arms" using small diameter cord for my experiment.
I must admit that it did lean a bit toward the horizontal sections side due to uneven weight distribution.  I had planned to put a 3/8 inch wooden dowel inside the full length of the vertical section to strengthen it but never got around to that. I was having too much fun with it as I described it in this article!
We had some 25 to 30mph windy days and it did do a dance but remained in the air with no ill effects to swr or performance.

As an option, you can use another "T" and horizontal "arm" near the middle of the Slim Jim on the main vertical section for additional support of the antenna but of course, this adds additional construction time and material to the project. No part of the Slim Jim should touch the PVC....in my humble opinion.

You can use a larger diameter PVC than I used for more strength and change the instructions and materials to fit your needs but the whole idea of this "design" is to get the Slim Jim antenna away from metal and the PVC or its support as far as possible allowing it to operate in a more or less "free space" invironment...have fun with yours. 73 N4UJW

If you try this design, please let us know how it worked for you or if you have additional ideas that you would like to share with others that we can add here! Goog luck with yours and have fun!
n4ujw AT hamuniverse.com




 



  

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