1. First steps with FT140-43
The impedance of an End Fed Half Wave (EFHW) dipole lies in a range of approx. 2k Ohm to 4k Ohm. In order to achieve a reasonable matching at 50 Ohm, a transformer can be used.
As a starting point I simply copied the design of a broadband transfomer, using a ferrite toroid FT 140-43 from Amidon with a turns ratio of 3:24. The transmission ratio, which is the square of the turns ratio (1:8), is 1:64. This means an impedance of 3200 Ohms will be transformed to 50 Ohms. The above mentioned range of 2k to 4k will fall in a range of approx. 30 to 60 Ohms which results in a slight (but acceptable) mismatch.
There are several manuals available, e.g. here or here.
Edit 2021-11-03: There is a discussion on the SOTA-Reflector which indicates, that the cross-over winding technique causes additional loss. Apparently it is more efficient to make all windings as close as possible.