"Jerry" wrote in
:

....
What is the reasoning used to indicate 300 ohm line is used in (B)
of the
referenced http://www.vk1od.net/lost/Fig7.png .?

The figure is is from the ARRL Antenna Handbook.

In (b), the numbers are rounded. A nominal 280 ohm dipole via 1/4 wave of
400 ohm line gives 570 ohms at the tee. Two such branches are paralleled
for 285 ohms, which on 300 ohm main feed line line results in a VSWR of
1.05... should be acceptable.

Does that help?

Owen