" 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
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