Owen Duffy simulated a Common Mode Choke (CMC) using RG316 coax and 2643251002 toroid ferrite core . See his post here . I found the double-shielded RG316 coax I was using had a life of its own with regards to routing. My understanding is that windings close together boast capacitance, which can negatively affect the choking performance, especially at the high frequency end of the HF spectrum. I designed and 3D printed a part which solves this.
A Ham Radio Blog by ZL1HAZ