Microtest TSB-67 - 568A Annex E - Manual (Page 45)

Page 45
Testing for noise involves turning off all LAN devices and measuring for background electrical
activity in the cable. Often, noise problems can be corrected by moving the cable away from the
source or removing the source, if possible. Different noise sources radiate at different frequencies.
By knowing the frequency of the noise source, you are better able to pinpoint the cause of the
noise. Two Noise measurements are provided: Impulse Noise and Peak-to-Peak Noise.
Impulse Noise counts the impulses detected between wires in a pair, or the center conductor and
shield (when using a Coax jack). Impulse Noise measurements are used for long term monitoring
of the network. They indicate spikes of electrical activity that occur at random on the network.
Peak-to-Peak Noise measures continuous noise signals, in the range of 0 to 3,000 millivolts (mV),
between the wires in a pair or the center conductor and shield in the case of coax cable (when using
the Coax jack).
Impulse Noise
To display the IMPULSE NOISE screen, press the Measure Cable Performance key, then select
Impulse Noise .
A noise impulse is detected when it crosses the selected voltage level. When the selected voltage
level is positive, impulses rising above that level are counted. When the selected voltage level is
negative, impulses falling below that level are counted.
The wire pair being monitored is indicated in the upper left corner of the display.
The current time of day is displayed below the wire pair.
The box below the current time displays a graph of the impulses detected since the measurement
started. The graph can span a 25-hour period with each dot across the graph representing the
highest peak impulse in the last 15-minute interval.
The bar graph on the right displays the impulses per second, averaged over the last 10 seconds.
E.T. indicates the Elapsed Time since the start of the test.
Count indicates the cumulative count of impulses detected since the start of the measurement.
When the Count exceeds 65535, OVR (Over Range) is displayed. In an Over Range condition, the
last average CPS (Counts Per Second) recorded is displayed.
CPS indicates the average counts per second since the measurement started. The maximum average
counts per second is 200.0.
Press Pair (F1) to select a new pair to test. The results from the previously displayed pair are
cleared from the screen.
Press Clear (F2) to restart the test and clear all history data.
Press Level (F4) to change the voltage level for detecting impulses. The results from the previously
displayed pair are cleared from the screen.
Press the ESCAPE key to return to the Measure Cable Performance screen.