[TowerTalk] Fwd: Fwd: Fwd: RG-149: 50 ohm/70 ohm - does it matter?

[Paul Christensen]

>" If I recall my radio teacher, 50 ohms were decided sometimes during WW2 
>or even earlier. There were some switch from (I may be wrong here) from 50 
>to 52 ohms at one point.

Lots of folklore ranging from commonly available pipe diameters before WWII 
to the geometric mean of three important values: (1) Approx. 30 ohms 
represents a characteristic Z for optimum power; (2) 60 ohms for optimum 
voltage; and (2) 75 ohms represents a Z for minimal loss, all other factors 
being equal.

The geometric mean of 75-60-30 is 51.3 ohms and is a close approximation to 
either 50 or 52 ohms.

Paul, W9AC