16
Figure 12
HDTDX showing connectors at the
start and middle of the link.
On analyzing the HDTDX trace we see two pulses, one at the beginning 0.0 meters, one
in the middle at 6.0 meters and the end of the cable is at 11 meters, this showing us
the connectors in the link. Connectors should ideally be no worse than 30% on links
less than 15 m (50 ft.). We have drawn a horizontal line on the HDTDX graph at 30% so
it’s easier to see where 30% has been exceeded. The first connection clearly exceeds
30%. The pulse in the middle of the graph also exceeds 30%, so clearly shows another
connector in the middle of the link at 6.0 meters. This is not ideal! In addition, we see
some aberrations between the first and second pulse. This indicates NEXT along the
cable, maybe the cable has been damaged. Events in the cable should ideally not exceed
10%. If they do, there should be no more than four of them. Any which way, it looks like
we should recommend replacing this whole link to eradicate the middle connector and
maybe improve the NEXT because of the potentially damaged cable.
In the next example, shown in figure 13, we see another NEXT failure. Once again
we look for the worst case NEXT margin failure pair. In this example it’s pair 3,6-4,5.
Typically it’s always 3,6-4,5 that exhibits the worst case NEXT, by the nature of the
construction of the cable.
Figure 13
Next failure at -6.0 dB Margin
@ 267.0 MHz on Pair 3,6 -4,5
