Ref: 11420002
Title: Using the LanScanner
date: 8/1/89

Copyright 3Com Corporation, 1991.  All rights reserved.

The LanScanner is a diagnostics tool for qualifying preinstalled
coaxial and twisted pair cabling used with Ethernet.  It also
provides the capability to troubleshoot wiring problems in such
hard-to-reach spots as walls, ceilings, and cable trays.

The LanScanner provides menus for the user to specify the wire
type to be tested and to specify any of the following test
functions:  AutoScan, Manual Scan, Noise Detection, and DC Loop
Resistance.  The AutoScan and Manual Scan tests determine the
characteristic impedance of the cable in two-foot increments
along the cable.  The Noise Detection test checks for low
frequency noise and pulses that indicate a problem on the cable.
The DC Loop Resistance function measures the total resistance in
ohms throughout the entire length of a shorted cable.

Open cable and shorted cable are identified when the LanScanner
senses an abrupt change in the characteristic impedance, angling
sharply towards zero (shorted) or infinity (open).  If a
terminating resistor that matches the characteristic impedance of
the cable under test is placed at the end of the cable, then the
LanScanner will be fooled into believing the cable is of infinite
length.

Note:  Because the LanScanner is more accurate at sensing an
abrupt change in impedance toward zero than toward infinity, the
cable needs to be shorted at the end and not terminated.  Trying
to perform test functions through PairTamers, MultiConnect
modules, or in other situations where the cable is not shorted at
the end will not provide accurate results.


Using the Autoscan Function

The Autoscan test uses the time domain reflectory (TDR) to
automatically scan the length of the cable.  The scan continues
until the end of the cable is reached, or an impedance variation
which might significantly affect data transmission is found.

Note:  The autoscan cannot detect problems in cabling less than
twenty feet long.  Use the manual scan test on cabling shorter
than twenty feet.

To use AutoScan, follow these steps:

1.  Turn the LanScanner on by rotating the button until it stops.

    As the LCD lights up, the LanScanner will perform a self
    test.  When the self test is completed the LCD will show:

         Wire Type ?  >>
                      Coax

2.  Press the down arrow to accept Coax as the desired medium or
    press the right arrow to select twisted pair.

    After the medium is selected, the LCD will show:

         Function ? >>
                    Autoscan Coax

3.  Press the down arrow to accept the Autoscan Coax as the
    desired test function.

    After the test function is selected, the LCD will show:

         Prop Delay ? >>
                     66% Solid

4.  Press the down arrow to accept 66% solid insula or press the
    right arrow to select 78% foam insula.  (These are the two
    most commonly used cable installations.)

    The dielectric or insulating material used affects the Net
    Velocity of Propagation (NVP) of a signal through that cable.
    Solid dielectric usually results in a signal speed of 66% of
    the speed of light, or roughly .2 meters per nanosecond.
    Foam dielectric, on the other hand, does not crush the cable
    as tightly, and the signal typically can travel at 78% of the
    speed of light, or roughly .24 meters per nanosecond.

    Once the type of cable installation has been chosen, the
    LanScanner will start calibrating the cable.  If nothing
    wrong is found, the message "cable shorted at xy feet" (where
    xy is the total distance of the cable) will appear in the
    LCD.

    Note:  If the cable is shorter then 30 feet you will not see
    the ohms appear in the LCD while calibrating.

The Autoscan test function will give one of four test results:
"cable open," "cable shorted," "cable terminated," and "problem
found."

"Cable open" indicates a cable whose end is not shorted or
terminated; for example, if a terminator is missing or has fallen
off and a "net 804" error is showing up on a workstation.

"Cable shorted" indicates that the LanScanner has detected a drop
in impedance.  One of the more common examples of this is when a
50-ohm cable is attached to a 75-ohm cable.  The LanScanner may
not detect a short in a cable under 20 feet.  Use the manual
test function to test cable under 20 feet.

"Cable terminated" can cause the LCD to appear to keep moving to
infinity when the scan reaches the end of a terminated cable.
This is why the cable must be shorted at the end, not terminated,
to give accurate readings throughout the length of the cable.

The LanScanner displays "Problem found at xx feet" if it senses a
significant change in impedance, but the slope is not sharp
enough to determine whether the cable is open or shorted.  This
can indicate a stretching of the cable, a change in its
characteristic impedance, a transition from one cable type to
another, or other serious problems.


Using the Manual Scan Test

After performing the autoscan test, it is a good idea to perform
a manual test on the cable to test the accuracy of the autoscan.
You MUST use the manual scan test if the cabling is less than 20
feet long.

Note:  If the manual scan is run after the autoscan, the manual
scan will start from the outermost point of the cable and work
inward.

    Select manual scan by choosing the downward arrow key again
    after the autoscan is complete.


    To run a manual scan without first running autoscan, display
    autoscan in the LCD.  Next, choose the right double arrows
    until Function ? Manual Scan appears in the LCD.  Then choose
    the downward arrow key to prompt you for the desired test.


The Noise Detection Test

This test checks the media for low frequency noise and pulses
that would indicate a problem on the cable.  Low frequency noise
usually indicates that the cable is either already hooked up to a
transmission device or that the cable is situated near something
which is causing interference, for example, if the Ethernet cable
is strung over fluorescent lights.  Other possible causes of low
frequency noise could be running an AC power line inside the same
conduit as the cable under test, inducing a 50 Hz hum in the
cable.

Pulses due to power surges, spikes, or crosstalk from other
electrical devices are also detected during this test.



The DC Loop Resistance Function

The DC Loop Resistance function measures the total resistance in
ohms throughout the entire length of the shorted cable.  The DC
loop resistance measurement is used to calculate maximum distance
when mixing twisted pair and coaxial cable within a single
segment.

To run the DC Loop Resistance function, perform the first two
steps shown in the Autoscan procedure.  Then at step 3, press the
right arrow twice to select the Noise Detection Test.
