[time-nuts] 50 vs 75 ohm cables

Poul-Henning Kamp phk at phk.freebsd.dk
Fri May 11 16:00:36 EDT 2007


In message <20070511192656.3E5ECBE1F at ip-64-139-1-69.sjc.megapath.net>, Hal Murr
ay writes:
>
>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 have no idea, but I recently read about the introduction of coax
in the Danish tele networks and it was said in so many words that
75 Ohms had a significantly longer reach.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.



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