A good clue that a reflection is actually a ghost from a
bridged tap, is that the distance from the end of the cable
to the ghost is the same length as the lateral itself (the
distance from Points D to E in Figure 6a is the same as
Points B to C in Figure 6a). A way to test whether or not
Point E is a ghost is to have someone short the end of the
cable. If Point D reflects downward along with Point E
when the cable is shorted, then Point E is a ghost
reflection of the bridged tap.
When testing through bridged taps, the signal strength
is cut in half, because a lateral provides a second path
for the signal. Point B in Figure 6b is where the signal
splits, and because of this, the maximum distance read-
ability is reduced from that point outward. If you can
normally test 6,000 feet in a particular pulse width or
range, you may only be able to see 3,000 feet beyond
due to the bridged tap.
4.3 Moisture in twisted pair
A subscriber complained about a noisy telephone line.
The noise was traced to the drop. The subscriber had a
2,800 foot two-pair drop to the home, along a country
road ditch, through the yard, and into the house. The
unused pair was found to be quieter so the customer was
switched to the quieter pair. This seemed to solve the
problem until a few months later, when the customer
started complaining again.
Retesting the pairs found the original pair was now
quieter. Noisy pairs going quiet and quiet pairs becom-
ing noisy led the technicians to suspect water in the
cable. Plant records showed the cable was not spliced so
it was unknown how and where the water was getting
into the cable.