Type 519 -- Why 125 ohms? Zo formula

Jeff Kruth

Hi Sean!A reasonable swag is that it is about the top end of coax impedance, hard to make a higher Z as OD of inner conductor gets vanishingly small. 73Jeff Kruth In a message dated 5/10/2021 9:54:24 PM Eastern Standard Time, sdturne@q.com writes: 
Pondering the beast that is sitting in my lab got me thinking, why 125 ohm? Does anyone know of the history of why this was chosen? I haven't been able to find much about this, so insights are appreciated! Sean