1 KW 4:1 Ruthroff (Voltage) Balun
Channel: Todd Mitchell
Date: 2011-10-17

This 4:1 Ruthroff (voltage) balun is constructed with 14 bifilar turns of stranded, teflon-insulated 14 AWG wire on two FT-240-61 toroids. The toroids are stacked and taped together with Scotch strapping tape. I also used narrow strips of strapping tape to tightly bind the two wires together, ensuring a capacitance as close to 100 ohms as possible. The enclosure is a weatherproof PVC box available at Menards for under $7. It came with its own neoprene gasket, and I used neoprene washers for each bolt as well as silicone sealant on all the bolts but the binding-posts. I built this 4:1 voltage balun for a New Carolina Windom antenna (which depends upon some common-mode current on the feedline below the balun -- if you're building an OCF dipole instead, you'll want to build a current balun instead of a voltage balune). With two cores and teflon wire, it should handle a full kilowatt. Total price of materials was about $40. 73! Todd Mitchell, NØIP, Granite Falls, Minnesota.