Attenuation to Crosstalk Ratio (ACR)
Attenuation to Crosstalk Ratio (ACR) is the difference between
NEXT and the attenuation for the pair in the link under test.
Due to the effects of attenuation, signals are at their weakest
at the receiver end of the link. But this is also where NEXT
is the strongest. Signals that survive attenuation must not
get lost due to the effects of NEXT.
Using PSNEXT and attenuation, Power Sum ACR (PSACR) can also
be calculated. PSACR is not required by TIA/EIA 568-B. Some
field testers will report it anyway. However, if you desire
PSACR you will need to specify it's requirement in the statement
of works document.
During signal transmission over twisted pair cable, both
attenuation and crosstalk are active simultaneously. The combined
effect of these two parameters is a very good indicator of
the real transmission quality of the link. This combined effect
is characterized by the Attenuation-to-Crosstalk Ratio (ACR).
ACR is nearly analogous to the definition of signal-to-noise
ratio. (ACR excludes the effect of external noise that may
impact the signal transmission.)
Results Interpretation
ACR is an important figure of merit for twisted pair links.
It provides a measure of how much 'headroom' is available,
or how much stronger the signal is than the background noise.
Thus, the greater the ACR, the better.
Troubleshooting Recommendations
ACR is derived from NEXT and attenuation data. Any steps taken
to improve either NEXT or attenuation performance will improve
ACR performance. In practice, this usually means troubleshooting
for NEXT because the only way to significantly improve attenuation
is to shorten the length of the cable.
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