KX3 - Balun
Posted by
Steve KC8QVO on
Sep 01, 2012; 11:47pm
URL: http://elecraft.85.s1.nabble.com/KX3-Balun-tp7561948.html
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¤t=IMG_9333.jpghttp://s118.photobucket.com/albums/o117/KC8QVO/QRP%20Projects%20and%20Stuff/?action=view¤t=IMG_9334.jpgI 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