A few further comments.

For perfectionists, the attenuation along a twin-line wound on a choke
balun, is appreciably less than a coaxial line of about the same
length.

This is due to the lower Zo of the coax and also due to the very small
inner coaxial conductor diameter and its higher loss resistance.

This is not of great conseqence. The length of line involved is quite
small anyway. Less than 1/8th wavelengths at the highest frequency of
interest.

The power-handling and voltage-handling ability of twin-line is also
greater than coax line.

So, in general, a choke balun wound with Radio Shack, 18 SWG speaker
cable, is cheap, easier to construct, works better, and is more power
efficient than the small-bore coax usually used.
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Reg, G4FGQ