Fluke DTX-1800, Technical Reference Handbook

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Certifying Twisted Pair Cabling
Twisted Pair Autotest Results
3-13
3
About dB Rules
For some test limits, the results from some tests are ignored
when a measurement is less than a certain value. For
example, for all limits where return loss is measured, the
return loss measurement is not evaluated against a limit at
frequencies where insertion loss is less than 3 dB. This is the
3 dB rule.
When a measurement is not evaluated against a limit, the
tester shows an
i
for the result. On the plot for that
measurement, the limit line is black where the result is not
evaluated. When you upload the results to LinkWare, N/A
shows for the result.
The following sections summarize the dB rules. Tables 3-2
and 3-3 show the dB rules that apply to each test and the
test limits that use the rules. For more information, see the
Knowledge Base on the Fluke Networks website.
3 dB Rule
This rule applies to all test limits where return loss is
measured.
At frequencies where insertion loss is less than 3.0 dB,
return loss is not evaluated against a limit.
4 dB Rule
This rule applies to the following test limits:
•
ISO/IEC 11801
•
EN 50173
•
Aus/NZ
•
JIS
At frequencies where insertion loss is less than 4.0 dB, the
measurements shown in Tables 3-2 and 3-3 are not
evaluated against a limit.
12 dB Rule
This rule applies to the following test limits:
•
ISO Class Ea Ch AMD1
•
ISO Class Ea PL2 25N1599
If insertion loss is less than 12 dB at 450 MHz, a relaxed
NEXT limit is used. See the Knowledge Base on the Fluke
Networks website for details.
67 dB Rule
This rule applies to all channel and permanent link test
limits where PS ACR-F is measured.
At frequencies where PS FEXT is less than 67 dB, PS ACR-F
cannot fail.