K0GKJ – Just Another Ham
The New QTH – A Floating Shack

Base Station VHF Copper Slim Jim Antenna Construction Complete

Tonight I put the finishing touches on the two meter copper tube slim jim (“slim” for its narrow form factor, and “J.I.M.” for “J-type Integrated Matching). Supposed to have about 6db gain over a 5/8 wave or groundplane antenna due to its small take-off angle which gives it extra punch, I guess. Can’t wait to tune it up and try it out. Currently, I’m strictly mobile on 2M. Check it out. This was fun to build:

 vhf antenna 001

At only 58 inches in total length, you can stick this thing (invisibly) just about anywhere. Here’s a little more detailed view of the tuning mechanism:

vhf antenna 002

The heads of the two outer 1/4×20 carriage bolts 3/4″ long simply rest against the two respective tubes (one is 3/4 wave long, the other 1/4 wave). The wing nuts on these two bolts receive the center conductor and shield respectively of the coax feedline. The center bolt, 1.5″ long, is simply a clamping device to hold this tuning mechanism in place. I’ll use my MFJ259B antenna analyzer to tune for lowest VSWR by sliding this mechanism up and down to find the sweet spot. Then I’ll mark the spot on the antenna where the feedline should be attached and solder in place (removing the temporary tuning device, saving it for the next J-pole-type antenna project. Then up on the roof she’ll go.

But first, I’ll put the darn tuning device on the correct end of the antenna! In looking at the pic above, I just noticed I screwed the darn thing onto the wrong end of the antenna! Oh well, my very first mistake in life had to happen sooner or later!

One pointer I recently picked up is that close-clamping such an antenna even to a non-conductive support (like a PVC or fiberglass mast) is likely to detune the antenna somewhat, so it’s best to stand it off a few inches with a couple of short non-conductive stand-offs (short lengths of PVC, for example, with the ends cut to the contour of the antenna and your mast. Always something to be learned!

73 de Gene K0GKJ dit dit

Advertisements

5 Responses to “Base Station VHF Copper Slim Jim Antenna Construction Complete”

  1. Hello just come across your article on the slim jim and i really like your feed attachment idea, the way that it can be slid up or down for best results is fantastic well done

    I am now going to have a go my self

    73 Gino G4nnz

  2. Just read your project. GREAT idea for the “tuning tool”
    73’s Mark KC6OVH

    • Thanks, Mark. Wish I could take credit for it. Improved on someone else’s idea (that’s what hams do, right?). 73 dit dit

  3. Very Good antenna ! I ve built with RG6 and also with cooper tubing , very good performance for 2 mts.Luis CD6419


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: