Comment on Making a 1:1 Balun for Amateur Radio
pageflight@piefed.social 1 day ago
This has been puzzling me: The point of coax is to keep all the field inside the coax. But the way a toroid works is to interact with the field. Why doesn’t that prevent the balun from working when coax is used? From what I’ve been reading, is it that the balun is only affecting the current on the outside of the shield by design?
fullsquare@awful.systems 1 day ago
exactly, the ferrite only affects common mode current. you can think of coax as being composed of 3 conductors, core, interior of shield and exterior of shield. above some frequency and below frequency where coax starts to work like a waveguide, internal surface and core carry opposite currents (differential mode), and external surface carries common mode current. these can be treated as separate, except at the ends, because of skin effect. but also you can use twisted pair, because differential mode currents cancel out there