For Geeks @nd the not so Geeky

Ethernet Cable Speeds – Fiber Optic & Maximum Length

Ethernet Cable Installation

  • Wave — energy or disturbance traveling from point A  to B
  • Amplitude — height of the wave (V)
  • Period — amount of time that it takes to complete 1 cycle or period between waves (s)
  • Frequency — the number of complete cycles or waves per second (Hz)

Pulses and Sine Waves

A pulse is a disturbance that was deliberately created with a fixed or predictable duration. Pulses are an important part of electrical signals because they are the basis of digital transmission. The pattern of the pulses represents the value of the data being transmitted. 100 ft ethernet cable

Sine waves, or sinusoids, are graphs of mathematical functions. Sine waves are periodic and display the same pattern at regular intervals. Sine waves also vary continuously meanings that no adjacent points on the graph have the same value.

Square waves are likewise periodic but unlike sine waves they do not continuously vary with time. Their value stays the same  to then suddenly change only to return to the original value at regular time periods. Square waves represent digital signals or pulses and can be measured in terms of amplitude, period, and frequency.

Installing Ethernet Cable and Noise

There are many possible sources of noise

  • Data signal carrying cables in the vicinity
  • Radio Frequency Interference or RFI from other signals that are transmitted nearby
  • Electromagnetic Interference (EMI) or Radio Frequency Interference (RFI) due to electromagnetic induction or electromagnetic radiation coming from artificial or natural external sources such as motors, lights, the sun or even the Northern Light.

Similarly to white light, white noise is a random signal that affects all frequencies as opposed to narrowband interference which only affects a small range of frequencies. In ethernet cable data transmission white noise will completely disrupt data transmissions while narrowband interference would only affect some signals.


Analog bandwidth refers to the range of frequency between the highest and the lowest frequency components and is measured in Hertz .

Digital bandwidth measures the throughput of data in a given amount of time. (bps) In general, media that will support higher analog bandwidths without high degrees of attenuation will also support higher digital bandwidths.

Make Your Own Ethernet Cable Considerations

Attenuation is the general loss in flux or signal amplitude over the length of an ethernet cable or other medium. The longer the ethernet cable and the higher the signal frequency the more signal attenuation will occur. The maximum length of ethernet cable should not exceed 100 m.

Attenuation on a cable is measured with a cable tester using the highest frequencies that the cable is rated to support. Attenuation is usually measured in negative units of decibels numbers. The lower the dB values the higher the ethernet cable speeds so 2 dB would be better than 4 dB.

In ethernet cabling the length of the cable and the frequency of the signal is a major factor in contributing to attenuation. Defective connectors, a bad ethernet cable patch, bad insulation or resistance of the wiring all have their influence on signal degradation, signal loss or attenuation.

Impedance relates to the resistance, capacitance, and inductance of the ethernet cable to the electrical current and is measured in ohms. Category 5 cable are typically rated at around 100 ohms. Improperly installed connectors will have a negative influence on the impedance on a Cat 5 ethernet cable causing an impedance discontinuity or an impedance mismatch.

Return loss or impedance discontinuities occur when  a portion of a transmitted signal is bounced back due to an incorrect connector or a cable fault. The higher the network speed the more pronounced the problem will be as the discontinuities cause additional portions of the signal to be reflected back to the transmitter.

Cross Talk

Cross talk is extreme noise generated by the signal traveling down the wire thereby creating an electrical field which interferes with any wires close by. The twists in ethernet cables are supposed to prevent this.

  • Near-end Crosstalk (NEXT)
  • Far-end Crosstalk (FEXT
  • Power Sum Near-end Crosstalk (PSNEXT)

Cable Testing Standards

The ten primary test parameters that must be verified for a cable link to meet TIA/EIA standards are

  • Wire Map
  • Insertion Loss
  • Near-end Crosstalk (NEXT)
  • Power Sum Near-end Crosstalk (PSNEXT)
  • Equal-level far-end crosstalk (ELFEXT)
  • Power sum equal-level far-end crosstalk (PSELFEXT)
  • Return Loss
  • Propagation Delay
  • Cable Length
  • Delay Skew

Cable Wire Map Problems

  • Reversed-Pair Wiring Fault
  • Split-Pair Wiring Fault
  • Transposed-Pair Wiring Fault


Propagation delay in ethernet cable testing measures the amount of time it takes for the signal to travel from point A to point B or from the sender to the receiver end. The electrical properties, length and twist rate of the cable all contribute to the delay which is measured in hundredths of nanoseconds.

A Time Domain Reflectometry (TDR) test is not only used to measure the length of  a cable but also to locate faults and discontinuities  such as shorts and opens.

Delay skew refers to the difference in transmit speeds or propagation delay of the multiple twisted pairs that make up an ethernet cable. Delay skew is determined by measuring the difference between the wire with the highest delay against the wire with the lowest delay.

Fiber Optic Ethernet Cable

Fiber optic ethernet cables send signals over hair thin strands of glass fiber and eliminate crosstalk or noise problems. Just like tradirional coper wire UTP cables, improperly installed connectors will greatly reduce the data transmission speed.

A fiber optic ethernet cable uses light to transmit data and as such is also susceptible to optical discontinuities that will reduce the speed of the data arriving at the receiver.

Power over Ethernet Cable

Power over Ethernet (PoE) is very much self explanatory in the sense that it consists of a technology which enables electrical power to safely use the same ethernet cable.



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