Your DTX CableAnalyzer has the ability
to figure out whether a near-end
crosstalk failure was caused by a cable
or a termination issue.
In this example, taken from the field,
it was caused by a cable issue.
And I'm going to walk you through the steps
to prove that it is a cable issue.
This is the kind of thing that
resolves disputes that can last for weeks
and nails it within a matter of minutes.
So, with near-end crosstalk highlighted,
we see that we have a margin of -0.9 dB.
I'm going to hit the ENTER key,
and that's going to give me
all six pair combinations.
I'm only interested in the pair
combinations that gave me that -0.9.
So, hit f3 key
and we find out that it's pair 1,2-4,5
that's shown in the top left-hand corner here.
And again, just before, we have
this nice smooth line, which is our limit
above is good, below is bad.
But we see that at 233 megahertz
it dipped below the limit line
and that's what's causing the failure.
Alright, so we know it's 1,2-4,5.
Next step, hit the EXIT key,
EXIT key and page down
to something called HDTDX analyzer.
This is that tool I was talking about
in previous modules that allows you
to look down the cable and see where
the crosstalk is happening.
I'm going to hit the ENTER key.
And, yes, just as before it's going
to give us all 6 pair combinations.
I am only interested in that
failing pair, 1,2-4,5.
I can locate that by just pressing the f3 key.
Once more.
And that gets me to 1,2-4,5.
Now, you may quickly observe
that we seem to have a little bit more
crosstalk going on in the cable
than we would normally expect.
Each end seems to be okay
suggesting that the
terminations are good.
Now, what we're going to do,
is we're going to press the f2 key,
which is our zoom key,
and I'm going to press the up arrow key
until I see 8X in the top right-hand corner,
and 12.5 here, and -12.5 here.
why have I done that?
A general rule of thumb,
and it's not in the standards
this is just a diagnostic tool,
is that we don't want to see
more than 5% happening in the cable.
So, 5% just so happens to be a little bit
less than halfway on the screen here.
Let's put in those two 5 markers.
Let's put in the 5% marker across the top,
and the 5% marker along the bottom.
Now, in reality,
it is normal to get one or two events to
exceed that 5%. That's going to happen.
It happens in the real world. However,
on this occasion here, we have many, many
events exceeding the 5% or minus 5% rule.
We can categorically say, without any doubt,
we have a cable issue.
And it doesn't matter how many times
you terminate this cable;
it's not going to get you beyond
even a marginal pass. You may be able
to get a marginal pass by putting on
a better connector, but it's still going
to be right on the edge. And your
customer is going to be asking questions.
Now, just to put that into perspective,
I'm going to hit the f3 key
and look at one of the other pairs.
That looks just fine.
So you can get a sense of scale
as to what we're talking about here.
And, so, let's review the procedure:
find out which is the worst-performing pair;
go to the HDTDX;
look at that worst-performing pair;
change the zoom to 8X
in the top right-hand corner;
and look and see how many events
exceed roughly about halfway up the scale
and halfway below the scale.
And if they exceed three or four,
then you want to start getting nervous
and, unfortunately, you have a cable issue.
And that cable is going to have to
be replaced.
And that is how you diagnose a cable issue
using your DTX CableAnalyzer.