PMG, Course of Technical Instruction (old) says that the 276Log(2D/d) is
inaccurate when the clearance between the wires is small compared with
the wire diameter. The book goes on to say that the acosh formula is an
accurate one for all spacings. No mention is made of efffects of skin
depth et al on Zo.
Alan


Owen Duffy wrote:
I have found two common expressions for the Zo of a two wire line in
space.
..............
This suggests (states) that the acosh expression (fully) accounts for
proximity effect on Zo.

Comments?

Owen