Specifications

G
G5
STRUCTURED
CABLING
NETWORK CONNECTIVITY SYSTEMS
www.signamax.eu
ACR (Attenuation to Crosstalk Ratio)
ACR is a theoretical parameter (i.e. it is not measured but is
deduced from two previously measured values) which shows the
margin between the NEXT and attenuation values: ACR [dB] =
NEXT [dB] - A [dB]. If the level of attenuation meets or approaches
the level of near end cross-talk, the transmitted signal will be lost.
The interval between NEXT and attenuation must be at least 10 dB.
What to do if the ACR parameter fails?
As the ACR parameter is dependent on the NEXT as well as
attenuation values, an improvement of these two parameters will influence the resulting ACR values.
FEXT (Far End Cross Talk)
FEXT expresses the cross-talk of the signal from one pair to another pair within one cable measured at the
far end. This is the same parameter as NEXT, only with FEXT, the measurement is done at a different cable
end. Again, all combinations of pairs are measured within one cable—i.e. 12-36, 12-45, 12-78, 36-45, 36-78,
and 45-78. FEXT servers an important basis for the following ELFEXT parameter.
ELFEXT (Equal Level Far End Cross Talk)
ELFEXT corresponds much better to the actual situation during data transfer than FEXT. It is because the cross-
talk inside the cable decreases as the attenuation increases. Just as with ACR, ELFEXT is a theoretical
parameter (i.e. it is not measured but is calculated from other previously measured values): ELFEXT [dB] =
FEXT [dB] - A [dB]. Thus ELFEXT is the cross-talk at the far end decreased by the attenuation.
PSNEXT (Power Sum NEXT)
PSNEXT is a theoretical value calculated from the previously measured NEXT. The PSNEXT parameter is
primarily important for protocols that use all four pairs for signal transfer (e.g. Gigabit Ethernet). The output sum
of cross-talk at the near end shows how much signal gets from three pairs to the remaining fourth pair. The
source of the signal and measurement of cross-talk takes place at the same end of the cable.
What to do if the PSNEXT parameter fails?
Just as with other parameters, PSNEXT is also influenced by the measured values of NEXT. Thus, an
improvement in the near end cross-talk value will affect the resulting value of PSNEXT.
PSELFEXT (Power Sum ELFEXT)
PSELFEXT is calculated from the ELFEXT value. Just like PSNEXT, this parameter is important for protocols
that use all four pairs for signal transfer. PSELFEXT expresses how much signal in the same cable gets from
three pairs to the remaining fourth pair. The source of the signal and measurement of cross-talk takes place at
opposite ends of the cable.
Propagation Delay
This value expresses a delay of the signal travelling from one end of the cable to the other. The typical delay
of the signal in a category 5e cable is around 5 ns per 1 m; the permitted limit is 5.7 ns per 1 m, which is 570 ns
per 100 m. Propagation Delay also serves as a basis for testing the Delay Skew value.
Delay Skew
Delay Skew shows the difference in signal delay between the
fastest and the slowest pair. The Delay Skew parameter is
affected by (1.) different length of the pairs; (2.) difference
in material (resistance, impedance etc.); (3.) the effect of
surrounding interference. If the difference is too great, there
can be an incorrect interpretation of data by the active device
(usually a switch, network card, etc.). Just as for PSNEXT and
PSELFEXT, the Delay Skew parameter is critical for protocols
that use all four pairs, such as Gigabit Ethernet.
P1
P2
Structured Cabling Testing
Bytes sent
Bytes received