This is a the “magic” behind the CHA-250HD, the transformer matching section.
The transformer on the original CHA-250 had smooth sides. The current version has a heat sink to dissipate heat created inside the transformer.
Yes, some of the RF that enters the power feeding section is turned into heat rather than transmitted as RF, but that is one of the compromises needed to create a broad-band, low SWR, multi-band HF antenna with minimal visual mpact.
