Choke Balun re Common Mode Currents.

Conventional wisdom, in some technical handbooks, seems to imply that coax coils wound on a toroid should not exceed six wide spaced turns (three one way then three in reverse) in order to avoid capacitance between the braid windings.

I tried that but I was disappointed with the performance. I noted that on some websites it was indicated that twelve turns would be successful... so I went for fourteen. (Seven one way then seven in reverse.) Bingo! Faultless performance across the HF bands at 15W. YMMV. If the toroid gets hot then ease off the power. You may destroy the toroid properties if it gets too hot.

In photo below you can see that I used RG58 C/U, FT240-31 toroid and plastic cable ties.

(When winding the toroid wear safety eye protection as the RG58 could easily flick into your eyes.)

Choke Balun re Common Mode Currents.