26 Jun
2018
26 Jun
'18
5:46 p.m.
So then we're in agreement that screwing the N terminator directly to an
intrusive tap shouldn't make a difference? No need for a jumper off the end
of the tap for the terminator to live on?
As a high school CCNA hopeful, I accepted this as, "it's what you do," and
I hadn't really given it any thought since then, as I hadn't had to mess
with thicknet since then. I agree that it doesn't really make sense when
you actually *think* about it, and, like I said to start with, it's what I
recall being told back then anyway -- I could be remembering wrong to start
with :)
Thanks,
Jonathan
On Tue, Jun 26, 2018 at 8:02 PM, Paul Koning via cctalk <
cctalk at classiccmp.org> wrote:
On Jun 26, 2018, at 7:20 PM, Eric Smith via
cctalk <
cctalk at classiccmp.org> wrote:
On Tue, Jun 26, 2018 at 4:37 PM, Chuck Guzis via cctalk <
cctalk at classiccmp.org> wrote:
no
On 06/26/2018 03:15 PM, Grant Taylor via cctalk
wrote:
If the termination resistance matches the characteristic impedance of the
cable, there should be no difference. When terminated properly, there is 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. 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.
Exactly. And the specs for the Ethernet terminator are quite tight for
that reason. The connectors themselves have non-zero impact but very
small; they are high quality microwave grade connectors.
You got the definition precisely correct: a terminator is a device that is
electrically equivalent to an infinite length cable. You can cut the
unused part of a coax anywhere you want and put a terminator at that point
instead, and as far as the rest of the cable is concerned nothing has
changed (apart from very small effects because the components are not
perfect).
There clearly is confusion about what terminators are and how they work.
It's all perfectly straightforward elementary classic E & M, and any
halfway decent RF theory textbook will make things clear. Even a source as
elementary as the ARRL Radio Amateur Handbook will serve.
paul