Even before entering the mystical realms of UHF design, radio frequency (RF) circuits come with a whole range of fun design aspects as well. A case in point can be found in transmission line transformers, which are commonly used in RF power amplifiers, with the Guanella transformer (balun) being one example. Allowing balanced and unbalanced (hence ‘balun’) systems to interface without issues, they’re both very simple and very complex.

Transmission line transformers are similar to regular transformers, except that the former relies on transmission line action to transfer energy rather than magnetic flux and provides no DC isolation. The Guanella balun transformer was originally described by Gustav Guanella in 1944. Beyond the 1:1 balun other configurations are also possible, which [Dr. Arar] describes in a follow-up article, and which are also covered in the [FesZ] video, alongside the explanation of another use of Guanella transformers: as an impedance transformer. This shows just how flexible transformers are once you can wrap your mind around the theory.

https://www.youtube.com/watch?v=QAYaetJ1dvM

“How much it affects a speaker cable, I dunno. Think of a speaker cable behind a typical hifi setup.”

Depends on amplifier how much RFI that gets to cable. Normally even a lot RFI can’t directly affect speaker elements directly. But the RFI enters amplifier, the amplifier electronics can act as rectifier which causes speaker output signal change when RF signal is preset or not. You hear this as noise on element.

#84: Basics of Ferrite Beads: Filters, EMI Suppression, Parasitic oscillation suppression / Tutorial
https://www.youtube.com/watch?v=81C4IfONt3o

Measuring ferrite beads
https://groups.io/g/nanovna-users/topic/35413448