[TowerTalk] Radio's/tunnels

[TexasRF@aol.com]

The impedance of coax is a function of conductor diameters and dielctric 
constant of the insulator. To maintain a 50 ohm impedance changing from solid 
dielectric to foam will require a larger center conductor. For example, RG213 
has a center conductor diameter of .0888 inches and LMR400 uses .109 inches. 
Both cables have the same shield diameter. The extra center conductor 
diameter allows about 24% more surface area which helps reduce losses. No 
doubt the air cells will have lower dielctric losses than solid poly so the 
answer is that both factors come into play in reducing cable losses.

73 de k5gw

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