Attenuation and Interference Issues
- if cable link too long:
- may result in decibel (dB) loss (insertion loss)
- the link experiences signal degradation problems with higher error rates and retransmissions
- results in reduced speeds and loss of connectivity
- measured in dB
- represent the ratio of received voltage to original voltage
- dB expresses the ratio between two values using a logarithmic scale
- is nonlinear
- small change in dB value represents a large change in the performance measured
- useful reference points:
- +3 dB = doubling, -3 dB = halving
- +6 dB = quadrupling, -6 dB = quarter
- +10 dB = 10 times the ratio, -10 dB = tenth
- max value allowed for insertion loss depends on link category
- E.g., Cat 5e at 100 MHz allows up to 24 dB
- smaller values are better
- cable certifier reports the margin, difference between the actual loss and the maximum value
- Electromagnetic interference (EMI) should be detect upon new cable installation