This was a very active thread some time ago on another list, so let me
toss in yet another "reason" for 50-ohm coax:
In WWII, someone was clever enough to research the relationship between
characteristic impedance and the amount of material(s) required for a
cable. The result was that 50-ohm cable won out as requiring less
copper (then a highly critical material) than other impedances.
This caused a lot of upset since it was conventional wisdom (then!) that
transmission lines should be 75 ohms or thereabouts to match the
impedance of a dipole!
I really suspect that 50-ohms came about as a result of all the thoughts
that have been offered.
-- 73, George Amateur Radio W5YR QRP-L #1373 AutoPOWER Systems Fairview, TX
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