Options and Accessories
3–10
1503C MTDR User Manual
Collision (-1.7 V) Output Signal is: Off/On
CAUTION.
The collision signal will stop most traffic on the network. This might
abort many application programs and might cause communications problems.
When this test is on, the 1503C will assert a -1.7 VDC level on a 50 load (-3.4
VDC open circuit). This signal is intended to be equivalent to the average of two
colliding Ethernet transmissions and should trigger the collision detect circuit on all
the transceivers. This should cause applications to back off and retry, then eventually
abort, as defined in the 802.3 standard. Therefore, it can be used to test units that
do not respond to this signal or to stop traffic for TDR testing.
Customizing Your Own Tests
Access the Acquisition Control Menu located under the Setup Menu. The various
tests listed can be used in any combination. Remember that the tests will not be
activated until you return the 1503C to normal operation, so any combination can
be chosen, then activated.
Waveform Signatures
By now you probably have a good idea what traffic looks like on the display and how
you can use the NOISE FILTER to reduce it. Other signatures might also appear on
the display.
Terminators are small reflections seen as stationary bumps and dips. A perfect
terminator would not reflect any energy, and theoretically would be invisible on the
1503C display. Because of small impedance differences between the cable and the
terminator, a small amount of energy will be reflected. The signature of a terminator
tends to go either up or down. Because a terminator absorbs nearly all the energy
of a pulse, the normal ripples in the waveform (minor changes in impedance) will
not be present after a terminator. The point where the waveform becomes flat is a
clue to the location of a terminator.
Taps commonly have a characteristic down-then-up reflection. The TDR pulse will
continue to travel past a tap because only part of the pulse’s energy is reflected. This
allows the 1503C to read signatures well beyond taps.
Following are examples of tests made on two Ethernet systems:
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