[time-nuts] 50 vs 75 ohm cables

Robert Atkinson robert.atkinson at genetix.com
Fri May 11 03:58:00 EDT 2007


It also uses less copper so the costs are less, important when lines are
measured in miles not feet!

Robert.

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Poul-Henning Kamp
Sent: 10 May 2007 21:53
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] 50 vs 75 ohm cables

In message <E1HmBTB-0006jt-SN at febo.com>, John Day writes:

>So 75 ohms as we 
>know it now is a compromise between the low attenuation 77 ohms and 
>the 73 ohm dipole feed-point.

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.

-- 
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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