Making a common mode choke out of bifilar windings has proven rather difficult. For me the difficulty lies in getting the impedance to remain a constant 50 ohms from on the HF bands. I've tried 14 gauge enameled and I've tried 18 gauge PTFE. The wires seem very sensitive to any kind of change in position.
I've been modeling the choke after the one shown on this tutorial. Also what's the deal with that design? It's like someone took a 4:1 guanella and just cut the connection that makes it 4:1. Turning it into to parallel 1:1 chokes.
Is there any disadvantage to simply using coax windings instead of bifilar? Can I just wrap 11 or 12 turns of RG-316 around a toroid? How much more choking impedance do you get from a bifilar choke?
The application here primarily on the 40m band. I was looking to build a simple in-line choke (SO-239 on both ends) as well as choke "balun" (SO-239 on one end and balanced terminals on the other). I was also entertaining the idea of a choke "unun" for use with an elevated quarter wave vertical. I would have a top lug connected to the center conductor; the shield would split off to two side lugs.