Triple-Play Service Deployment

104
Bridged taps
Bridged taps, or laterals, are excess lengths of wire that extend past
the subscriber or are spliced in along the span. Many un-used
bridged taps remain from when party lines were deployed and
two or more taps were made on every line. Over time, the extra
taps were cut and taken off the termination block, but left
connected at some point to the loop. They became buried within
the maze, and can be difficult to locate.
Bridged Tap
The signal (blue) splits off
at bridged tap and
heads toward end
Figure 4.11 Function of a bridged tap
Chapter 4: Troubleshooting the Copper Plant for IP Services
When the signal (gray)
reaches the end of the
tap, it reflects back (red)
and interferes with the
original signal
While they do not interfere with normal POTS service, bridged taps
cause undesirable reflection that can distort the high-frequency
signals in modern transmission technologies. They degrade the
performance of an xDSL circuit by causing signal reflections at the
splice point and at the end of the tap. These reflections become
noise in the circuit degrading DSL performance. Bridged taps also
add noise to the circuit by acting as antennas, picking up external
noise along the tap, and attenuate the signal at the wavelength
that corresponds to the tap length.