[Elecraft] KX3 - Balun

[Steve KC8QVO]

I have had some parts around for a while now that I intended to build a balun
out of. I finally got around to working on one over the past week or so (I
started last Sunday night and did all the rest of it this evening HI). 

My idea was to make a 1:1 balun that fit right on the rig for using the
internal tuner with a doublet, or any other balaned line fed antenna. 

Below are links to pictures of what I came up with.

http://s118.photobucket.com/albums/o117/KC8QVO/QRP%20Projects%20and%20Stuff/?action=view&current=IMG_9333.jpg
http://s118.photobucket.com/albums/o117/KC8QVO/QRP%20Projects%20and%20Stuff/?action=view&current=IMG_9333.jpg 

http://s118.photobucket.com/albums/o117/KC8QVO/QRP%20Projects%20and%20Stuff/?action=view&current=IMG_9334.jpg
http://s118.photobucket.com/albums/o117/KC8QVO/QRP%20Projects%20and%20Stuff/?action=view&current=IMG_9334.jpg 

I used parallel runs of about 15-17" of 18 gauge magnet wire, two stacked
FT-82-43 cores (Amidon), 3/4" stainless screws, two nuts, two flat washers,
two lock washers, two wing nuts, about 1" of 18g stranded speaker wire
(lead-in to the BNC connector), BNC connector for RG-58 coax, two small ring
terminals minus the plastic sleeve, and a small enclosure box from Mouser.  

The BNC connector is bolted to the enclosure. It is a crimp style. I
soldered the center pin then used the rear nut/bolt part passed through the
wall of the enclosure as the mount for the plug. It is a pretty slick idea
and quite rigid. There are 10 wraps of the magnet wire around the cores.
Wrapping the stacked cores was a chore. I did not use anything to bond the
cores together first (no tape or anything, just the wire). Once I had about
3-4 wraps on there it stiffened up but it was a trick. 

One addition I may make to the balun is a piece of plastic between the turns
and the ring terminal crimps along the sides. I would imagine having the
terminals that close (right against) the windings is not a good idea. 

I have another idea for a balun that is identically designed with a chassis
mount BNC connector (single hole, not the 2 or 4 hole flanges) for use as a
dipole feed point. I have a T80-2 Amidon core wound up already, again 10
windings of the 18g magnet wire. This fit too tight inside the small square
enclosure but I have some that are rectangular and will have about twice the
vertical space. This will let me space out the ring terminals at the top as
well as have plenty of space for wiring the bulkhead BNC connector on the
bottom. 

Steve, KC8QVO



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