[time-nuts] 50 vs 75 ohm cables

Robert Atkinson robert.atkinson at genetix.com
Thu May 10 09:35:58 EDT 2007


Good question, likely to cause lots of discussion!
See 
http://www.edn.com/article/CA47191.html?industryid=2853&q=+2000+Why+50%3
F%3F%22+
 and 
http://www.edn.com/index.asp?layout=article&articleid=CA60931

Robert. G8RPI.

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Peter Vince
Sent: 10 May 2007 13:39
To: time-nuts at febo.com
Subject: [time-nuts] 50 vs 75 ohm cables

I came across some telecom equipment the other day which had 
reference outputs marked as 75 ohms.  I work in television, not 
telecoms, and we use 75 ohm connections for video, but with most RF 
stuff being (I believe) 50 ohms, and certainly all the HP and other 
counters seem to have 50 ohm inputs, I rather assumed telecoms used 
50 ohms - obviously not!  Can anyone tell me how and why the 50/75 
ohm distinction came about?  Was it perhaps a VHS/Betamax type issue 
with different manufacturers going their own ways, and then with so 
much equipment out in the field,  neither side was willing to change?

	Thanks,

		Peter (London)

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