In the past twenty years, cabling has made huge improvements for the UTP cabling. It was never expected to be able to send data over 10 Mbps, but now the data rates of 10 Gbps are supported. Future will proove that it is not the limit either. Cabling catalogs offer over 2000 types of cables, each design for specific purpose, and with specific project in the mind. The level of complexity is so high, it is difficult even for the specialist to select right cable for the right purpose. All these factors result in potential data corruption, signal loss, and signal degradation.
Developing cables that support higher frequencies, and data rates create new problems, that were irrelevant for lower signal frequencies. That means lots of testing is necessary in order to determine and define cable specifications, and its future implementation. Main tests are either related to attenuation (signal loss), noise, or delays.
Attenuation tests include:
- Conductor resistance
- Mutual capacitance
- Return loss
- Insertion loss
Loss of signal happens because signal quality degrades over the distance. It is important to note that after some particular distance signal will be so degraded that it will be impossible to receive it properly. Measurement is done by comparing signal difference at the sender and receiver ends in dBs. Difference will state the signal loss, which should be below some value specified in standards. Attenuation changes when the signal frequency is modified – higher frequencies usually result in higher attenuation. Another factor affecting attenuation is the temperature. Higher temperatures increase attenuation, while cold temperatures allow signal travel larger distances with less signal degradation.
Factors like core material and insulator specifications also affect the signal loss, as stated in previous article.
Noise tests mostly measure crosstalk value between cables and unbalance of magnetic fields cancellation. Source of the noise could be anything in the cable that is not the signal itself. More than that – origin of the noise could be outside the cable, and it would still affect the signal in the cable, even though there is an insulator in-between. One of the reasons that cables are twisted in pairs is the concept that noise that signal creates on the way from source to receiver will be partially canceled by the signal travelling in the opposite direction. Signals are balanced (as well as cables and insulators).
More important is to know that noise is not only thing that can affect cables. Crosstalk is a signal that “jumps” from on pair of cables to another one. This problem is also solved by twisting cables – crosstalk values increase with amount of twists done in the cable. It might be illogical, but higher crosstalk value in the cable specifications means less crosstalk in the cable.