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2.4 Factors affecting ADSL
Crosstalk
Whenever a current flows through a conductor, a magnetic field is set up around the conductor in a direction
given by the right-hand corkscrew rule.
Figure 79: Crosstalk
If we now bring another pair of conductors close to the first, the re-enforcing field created by the currents
flowing in the first line cuts through the plane of the new line, and this has the effect of inducing current into
the new line.
Attenuation
•
Reduction of signal strength during transmission (measured in dB)
•
Factors that affect attenuation
–
Distance of cable
–
Temperature
–
Wire gauge
•
Attenuation < 65 dB = OK
–
Clear capping helps reduce attenuation
Signal to Noise ratio (SNR)
•
Signal to Noise Ratio is the difference between the signal and noise floor
•
Measure of usable space between the signal and noise floor across the spectrum (upstream &
downstream)
•
SNR > 6 dB = OK
•
Excellent SNR, Upstream of 13.0 dB and Downstream 29.5 dB
Figure 80: Excellent SNR
•
Very poor SNR, downstream 7.5dB, upstream 4.0dB