Thicknet/10base5 Test Segment: The Cable is In!

[Eric Smith]

On Tue, Jun 26, 2018 at 4:37 PM, Chuck Guzis via cctalk <
cctalk at classiccmp.org> wrote:

> On 06/26/2018 03:15 PM, Grant Taylor via cctalk wrote:
>
> > I can only guess that having a terminator too close interferes with or
> > weakens the signal too much in some way.
>
> Exactly what would the effect be?  I recall putting terminators on
> 10base2 coax just hanging off one leg of a BNC tee.  Really, no distance
> at all.  Didn't seem to affect speed or distance.


If the termination resistance matches the characteristic impedance of the
cable, there should be no difference. When terminated properly, there is no
reflection from the terminator, so it looks equivalent to an infinitely
long cable, though in practical terms with less leakage than an "actual"
infinitely long cable would have.

Of course, in reality it will never be terminated perfectly, so there will
always be a small reflection, which can be seen with a TDR. If the
termination resistance is pretty close, the reflection will be small enough
not to matter at all for Ethernet.