Why 50 Ohms? The Readers Respond!
High Frequency Electronics
First, some background — In my June 2007 editori-al, I mused about the origins of 50 ohms as a standard impedance. I tried to search as far back as possible, and determined that analysis of coaxial line loss, power handling, voltage breakdown, etc. dated at least as far back as the 1920s, and there was a note about a specif-ic 50 ohm coaxial cable product in a 1936 text. I received many responses from readers, some of which confirmed portions of my own investigations, and some that offered more detail. Thank you to all who made a comment or offered a contribution to the discussion. It appears that 50 ohms is a compromise between maximum voltage and maximum power. Long before cable TV, and until the advent of fiber optical cables, multi-tube buried 75-ohm coaxial cable provided a great deal of long-distance multichannel FDM and PCM interconnection, especially in Europe, the former Soviet Union, and Japan.
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