26 Jun
2018
26 Jun
'18
12:26 p.m.
(re-send due to not reply-all'ing as required)
Sorry, I think that came across wrong due to my wording -- we were told it
wasn't general practice to screw the terminator directly to the intrusive
tap, as you would with a BNC tee on thinnet. We were told to use a jumper
to extend somewhat past the tap, if it was the last thing on the segment.
Ethan sneaked in a reply that mentions a lack of distance between the last
tap's impedance bump and the end of the transmission line. Perhaps someone
with more of a transmission line engineering background can confirm or deny
that.
Thanks,
Jonathan
On Tue, Jun 26, 2018 at 3:16 PM, Paul Koning <paulkoning at comcast.net> wrote:
On Jun 26, 2018, at 3:07 PM, systems_glitch via
cctalk <
cctalk at classiccmp.org> wrote:
I've confirmed that I now have N connector intrusive taps! These have a N
female connector on each end, like the leftmost transceiver in this
picture:
3_transceivers/DSC_0927_med.jpg
I seem to recall the CCNA instructor telling us that you weren't really
supposed to screw a 50 ohm terminator onto an intrusive tap; I don't know
if there's good reason for it or if it was just a general practice.
I'm not sure if I understood that correctly. It sounds flat out wrong,
and it presumably would not be general practice because an Ethernet segment
with a missing terminator either doesn't work at all, or works very poorly.
An Ethernet segment must have a 50 ohm terminator at each end (and nowhere
else). Always. The spec is crystal clear about this, and so is elementary
transmission line physics.
If you have an intrusive (connectorized) tap, installed at the very end of
the cable, the other side of the tap must have a terminator since that's
the end of the segment.
I once saw an article in a magazine ("DEC Professional" or "RSTS
Professional", a US based rag for PDP11 users) that talked about thick and
thin Ethernet. It mentioned that you can connect the two -- which is
correct. But it showed the wrong way -- with a T connector and a
terminator attached to one of the legs of the T. In other words, a
"terminator" in the MIDDLE of the segment. The correct way, of course, is
a BNC to N adapter, and you have to use the thin Ethernet length and
station limits.
So it sounds like your instructor was just as ignorant as the writers of
that magazine.
paul