In this example,
we see that crosstalk failed
with a margin of minus 1.3 dB.
That red asterisks to the right hand side
indicates it's a marginal fail
that's within the accuracy of the instrument.
When it comes to failing
a fail is a fail, so we need to diagnose this.
If we tap on near-end crosstalk (NEXT),
what's going to happen here is,
in this particular example, it's jumped to
the 6 measurements all the way from the far end.
Crosstalk is made 6 measurements
in one direction and then
6 in the other direction.
And we're interested in finding out
which is the worst performing pair,
because that's the one we want to diagnose.
If I tap the pair arrow on the right here,
we see that it's actually pair 3,6-4,5.
It could be 1,2-7,8. It could be
any of those combinations.
There's not too much more to be
gained from looking at this graph
in terms of diagnosing crosstalk.
I mean, we can see that it failed
at the top end of the frequency range
roundabout 500 megahertz.
Let's remember that 3,6-4,5.
Let's go back to the home screen.
We have a diagnostic tag
and we have two options on there:
we have HDTDR analyzer
and HD TDX. The R
in the HDTDR, return loss.
The HDTDX, crosstalk.
Of course the purists out there will say
TDR does not mean return loss.
You're absolutely right, it means
time-domain reflectometer.
But it's a good way to remember
which one's for return loss
and which one's for crosstalk.
Let's tap the crosstalk diagnostics.
You are immediately presented with
a time domain plot. That is the ability
to actually look down the cable
and see where the crosstalk is happening,
and it's going to show all six pairs.
We're only interested in that pair
that causes the problem, which was the 3,6-4,5.
So I'm going to go,
using that parent arrow,
so I get 3,6-4,5 to appear
in the top left-hand corner there.
The cursor will automatically go
to the largest source of crosstalk,
and it's gone to around about
51.4 meters, 168 feet.
This is the far end connection here.
Down here, we see our value of 45.7,
that's 45.7%. That's relative
to the vertical scale here.
What does that mean?
In an ideal world, we're looking for
better than 30%. Where the connections are:
30 to 35 is ho-hum;
35 to 40 you should start getting nervous
because you're going to start seeing a reduction
in margin on the near end crosstalk test;
and generally, anything over 40 suggests
that something didn't quite go right
during that installation.
When we look at this one here,
the firing connection is reporting 45.7.
That's simply too much crosstalk
going on in that remote connection.
Now, there are two possible causes there:
it could be a termination issue,
or it could be a non-compliant connector.
Now, we know for a fact in this one
that the connector they installed
was actually a true Cat6a connector.
So that means is,
it's probably a termination issue.
The good news is, we're not dealing with
a cable issue, because, when we
look down the cable,
we don't see anything.
Now, normally you would see
a few bumps going down there.
The general rule within the cable is,
if the event, the spike, is more than 10%,
be a little bit concerned.
If you get more than 4 or 5 of those,
then you're going to start to see
a bit of a cable issue happening.
But we don't see anything like that here.
Now, before we go off and terminate
the, reterminate the far end here,
we should probably check out on
their end connection here.
So I'm just going to move my cursor
all the way over to the right here,
and I put it to where my first connection is
and it's showing a value of 33.7.
Now, some people who interpreted my
knowledgebase articles as,
"well, if it's not 30 then it's a fail."
No that's, this is purely a guide.
So at 33.7, its ho-hum performance,
but
the far end is where our problem is.
So, the first thing I would do
is reterminate the far end.
And indeed, in this customer when
we reterminated the far-end correctly,
the margin came up and he got a very good pass.
That is how you diagnose
a termination issue
on the DSX 5000 CableAnalyzer
that caused a crosstalk issue