So.. I've been using a standard 1:49 imp. transformer wound with an 1mm dia enameled Cu wire on an FT240-43 core for my EFHW 80-10m antenna (3.5-29MHz).
Within my experimentation effort I've made a DIY "litz wire" - made of 60x 0.1mm enameled+cotton coated wires and used for a version 2 of my unun.
I've done some reading on that matter and they mention a "special weaving or twisting pattern of the wires in the bundle" is required in order to avoid various parasitic effects at higher frequencies (>2MHz). Is there any experience with the litz wire in such an application? Did somebody create a DIY litz wire suitable for such an application? Thanks!