From: Peter Vince <[EMAIL PROTECTED]> Subject: [time-nuts] 50 vs 75 ohm cables Date: Thu, 10 May 2007 13:39:27 +0100 Message-ID: <[EMAIL PROTECTED]>
> 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! No, it is 75 Ohm for unbalanced PDH signals such as E1, E2, E3 and E4 as well as the american DS1, DS2, DS3 and DS4. > 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? There where something about damping etc. Cheers, Magnus _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
