Introduction: Better Balun Boxes

Picture of Better Balun Boxes

I did an instructable on building a Balun or Unun.

A lot of people seemed to like it for their emergency go pack or field day kit bag. Since those boxes were out of stock I went to the Home Depot to see what kind of PVC electrical boxes they had.

There's a good selection but the boxes with no holes start around $8. Some of the ones with a conduit fitting molded in are under $2. No easy way to plug that without a big protrusion so I decided to make use of them.

Step 1: Custom 3D Printed Bushings

Picture of Custom 3D Printed Bushings

I made some bushings in OpenScad for some common parts like an SO-239 and some binding posts. I grabbed a bunch of different boxes with different configurations and some covers. I used PLA material and it seems to bond well to the boxes with standard PVC Conduit Cement.

Step 2: SO-239 Bushing

Picture of SO-239 Bushing

This was the first one I needed. I made a small relief for a ground wire under one of the screw holes. A little RTV will seal it but since I usually have this one pointed down I don't worry about that....

Step 3: 1/4-20 Posts for Wing Nuts

Picture of 1/4-20 Posts for Wing Nuts

These are pretty solid posts with a 1/4-20 hole down the center for a standard bolt. Use Stainless hardware if you are bored. I just use some automotive dielectric grease on the exposed metal. I bet a shot of Battery terminal spray after your wired up would work too.

I made these with a 50% infill and 6 shells to make them stiff enough to handle my overenthusiastic wrench use. maybe I'll make a recess for the nut on top but I do like to "KISS"

You can strap this to the top of a pole and hang an inverted Vee directly off the terminals.....

Step 4: Binding Post Bushings

Picture of Binding Post Bushings

Just a hollowed out version of the wing nut bushing. Good for light duty use or small go packs.Much prettier than the wing nuts but I wouldn't hang a dipole off these without some other support. The hollow and thin brass will snap.

Step 5: Other Uses

Picture of Other Uses

There are tons of other uses I can think of. Pilot lights, switches, headphone connectors, etc.

These tiny bushings have a ridge on top that can hold standard wire strain relief fittings.


ke8bg (author)2017-05-01

ust love our 3D printer for things like this. We've made replacement
keypad housings for VFDs here in the shop. Also some plug in card
handles for old VME bus cards. Do you have a thingiverse account?

rjkorn (author)ke8bg2017-05-01

I like making instant repair parts. someday i will put stuff on thingiverse. Right now work keeps me busy.

Thanks for checking out my ibles....

fossilshark (author)2015-03-15

so its a power supply? ive never heard of this before

rjkorn (author)fossilshark2015-04-21

Not a power supply but a form of matching device used to connect RF transmitters to less that perfectly matched antenna's.

this one is really just a high frequency transformer.....

supercazzola (author)rjkorn2017-04-15

thanks for sharing this design. I do have a quick question: isn't this an un-un, and not a balun, since it goes from unbalanced to unbalanced? Or did I mix this up with the previous generation that had the other (out of stock) box?

rjkorn made it! (author)supercazzola2017-04-15

It could be either depending on what you need. Its all about how you connect up the coil. BiFillar and TriFillar windings are most common. So many others have covered the winding principles better than I could so I focused on making a durable but cheap housing

This particular one pictured here is a balun I made for a dipole but It would have been equally at home on a vee or inverted vee etc..

My previous instructable pictured an un-un I used for a long wire along my fence with a ground rod alongside it.

you can see it here:

the giveaway that you have an un-un is the ground connection from the so-239 to the ground lead on top.

If you simply reverse the connections on the so-239 it becomes a balun

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