[Elecraft] Another feedline question

[Alan WB6ZQZ]

This has come up before.

Using two parallel coaxes as balanced line gives double the power capacity 
and double the impedance.

Line losses are unchanged over a single coax. Half the power is in each 
coax, and each half is subject to whatever db loss the coax normally has.

-- Alan WB6ZQZ

From: "Parker Buckley" <pbuckley@woh.rr.com>

...When one makes parallel transmission line from
two pieces of coax, say 50 ohm, shields connected, using the
inner wire as the transmission line to get 100 ohm line,
what is the theoretical loss of this line?  ...