My first 10BASE5 network segment

Paul Koning paulkoning at
Fri Aug 26 10:17:44 CDT 2016

> On Aug 26, 2016, at 11:00 AM, Ian McLaughlin <ian at> wrote:
>> On Aug 26, 2016, at 7:56 AM, Paul Koning <paulkoning at> 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.

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.


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