Tektronix 1503C, User Manual, Page: 74 / 128

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1503C MTDR User Manual
Longer pulses are more likely to generate collisions than shorter pulses. On
networks with traffic less than 3 to 4%, a 2 ns pulse causes no measurable change
in network statistics. Even on heavily tapped cables, the 2 ns pulse can usually be
used for distances to 700 feet. The 10 ns pulse should be suitable for those longer
segments that still fall within the 802.3 specifications (under 500 meters).
Single Sweep with Carrier is: Off/On
CAUTION. This can interrupt prior traffic and cause late collisions. It can also
disrupt devices or applications that require periodic network traffic.
When this test is selected, the 1503C will assert a -1.05 VDC signal on the net long
enough to take a single waveform at the NOISE FILTER level selected. This is the
equivalent to the average voltage level of a normal transmission and should cause
the transceivers to assert Carrier Detect. This has the effect of causing most devices
on the net to defer transmission until the 1503C is finished. This takes from about
one to 20 seconds, depending on noise averaging, and reduces the traffic displayed
on the waveform.
NOTE . Movement of any control that would change or move the waveform will start
a new sweep and assert the -1.05 VDC. For example, if you use the vertical position
control continuously for 20 seconds, you would be asserting the false traffic for that
duration and you are likely to disrupt the network.
Carrier Test is: Off/On
CAUTION.
This carrier signal will stop traffic on the network. This might abort many
application programs and might cause communications problems.
This test asserts the -1.05 VDC signal on the network, turns off the normal 1503C
pulse, and sets up the MAX HOLD mode. This is intended to help find transceivers
that have a faulty Carrier Detect.
To use this test, have the network prepared for disruption and turn the test on via the
Ethernet Menu. Any traffic observed is being transmitted in spite of a signal
simulating a carrier. This might be due to a transceiver not asserting its carrier detect
line, a host not reading its carrier detect line, or some other reason. This is not
unusual with some equipment. One way to isolate which units are doing this is to
disconnect them one at a time until it stops.