[time-nuts] 50 vs 75 ohm cables

[Hal Murray]

phk at phk.freebsd.dk said:
> I can confirm that the choice of 75 Ohm for telecom use indeed is
> because of the low attenuation.  The first use of coax was for
> "Carrier Frequency" systems, where a number of telephone conversations
> were AM modulated on individual carriers, usually 4 kHz apart. 

What's the attenuation mechanism?

I thought the old 10 megabit vampire-tap Ethernet picked 50 ohms because of 
lower attenuation.  The story I remember is that for a given outside 
diameter, the inside diameter was bigger at a lower impedance.  The main 
losses were resistive on the center conductor due to skin effect.  A bigger 
center conductor had more area at a given skin depth and hence lower losses.



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