26 Aug
2016
26 Aug
'16
8:17 a.m.
On Aug 26, 2016, at 11:00 AM, Ian McLaughlin <ian
at platinum.net> wrote:
Yes, I'm sure of that.
Splitters are a different story. A splitter is a device that has one input, terminated in
the cable characteristic impedance, and multiple outputs each of which are intended to be
connected to a properly terminated line. So for that reason, it is indeed correct that
unused splitter outputs should be terminated by the proper terminator.
But a T connector is not a splitter, which is why that analogy does not apply. Ethernet
(the baseband version at least) does not support splitters.
paul
On Aug 26, 2016, at 7:56 AM, Paul Koning
<paulkoning at comcast.net> wrote:
That reminds me of an amusing error in a 1980s trade rag for DEC users ("The DEC
Professional"). It discussed how you could mix 10Base5 and 10Base2 hosts by coupling
the two size coax cables through an N to BNC adapter. That's fine so long as you use
the 10Base2 limits. But instead of a barrel adapter, the article had a photo showing a T
connector at the transition, with a "terminator" attached to it. So that
network had three terminators: one at each end and one in the middle. I suspect it
didn't work, or at least quite poorly.
Are you sure about that? I?m by no means an RF expert, but, for example, the cable TV
plant is a huge tree of cables and splitters. They advise that all open sockets should
have a 75 ohm terminator attached to them. Even this whole mess with 75 ohm terminators
everywhere, and the characteristic impedance of the network is still 75 ohm. Remember this
is AC impedance, not DC resistance.