Weekend Projects, pt. 1: toroidal 1:1 current balun

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I got the bug to get some weekend projects going in the workshop, and this is the first of those.  I decided that I needed a 1:1 current balun for an upcoming ZS6BKW/G5RV ladder line fed doublet antenna, but it’s pretty important to make use of a 1:1 current balun to choke off the RF of the coax shield.  I also want something that will handle a full 100W safely without risk of sparking, overheating, or breaking down in some way.

I started with a 4″ x 4″ project box made by Hammond Manufacturing and a green 3″ diameter toroidal ferrite core made by Amico.  Not sure they’re the best, but it’s not a huge deal at HF frequencies.  It’ll likely have enough inductance to form a LC filter with the antenna as the capacitor (that’s what antennas are electrically to an AC signal) squelching off UHF and probably higher VHF frequencies from the feedline system.  I doubt it’ll affect 6M operation, but I lack the test equipment to know that for sure.

I then wrapped about 14 turns of 12 AWG zipline around the toroid and zip tied the ends in place.  I had a number of SO-239 panel mount sockets laying around, and I soldering the red lead to the center conductor.  I crimped and soldered a ring terminal to the black lead (it is the grounded shield…), and screwed that down with the socket to some holes I drilled in the project box.  I then crimped on ring terminals to both leads on the other end of the zip core wires, and then secured them with some #10 bolts, nuts, and washers I also had laying around the shack.  The KK4TSJ shack can be somewhat messy at times, but there is a system to the chaos.

Toroidal 1:1 Current Balun for HF Doublet Antenna
Toroidal 1:1 Current Balun for HF Doublet Antenna

After a lot of hot glue, the front panel, and some electrical tape, here’s the finished product.  I haven’t quite figured out mount to the mast system, but it’ll need to be mounted at a standoff to keep the mast from interacting with the ladder line up to the center insulator.  The Atlanta Hamfest is next weekend, June 7th, so I’m looking to pick up the rest of the supplies to complete the larger antenna mast project.

Ready for Hose Clamps
Ready for Hose Clamps

73 for now, DE KK4TSJ

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