65
Figure 3-59
Figure 3-60
Noise Filter
Electromagnetic Interference (EMI) or noise is everywhere in our environment
unless you are in a Faraday Cage or similar shielded room. Cables, particularly
unconnected cables, are also antennas. The type and amount of EMI they pick
up will be determined by the type of cable, coax or twisted pair, quality of shield
grounding. Since Step TDR’s are AC coupled to the cable under test any EMI or
noise induced on the cable will be seen on the display along with the TDR’s
reflections. Figure 3-61 is an example of a noisy cable. Noise can also appear
as intermittent spikes that appear in one trace and disappear 2 seconds later in
the next trace or change position along the trace.
Figure 3-61