In our previous Guide to Cat 5e & Cat 6 Cables we discussed the main differences and briefly showed the complex test structure required for true full Ethernet connectivity.
This week we are going to go into much more detail. Lets look at why the testing is so complex and why it is important that correct testing is carried out.
Firstly, the Copper conductors used to carry the data signals are being stretched to their limit and to achieve the required speeds every effort is made in the construction to make sure the best data flow is reached.
For example did you know that each of the four twisted pairs are twisted at different tightness? This ensures the very best data transmission rates with lowest crosstalk and signal loss. it’s small details like this that makes the copper conductors work to such high performance levels.
Now let;s look in detail at each test criteria. To be sure that the cable link preforms to the required standard it must meet the full 9 tests which can only be carried out by Network Analyzer.
The following is the full list of required tests:
Insertion Loss
Insertion loss, also referred to as attenuation, refers to the loss of signal strength at the far end of a line compared to the signal that was introduced into the line.
This loss is due to the electrical impedance of the copper cable, the loss of energy through the cable insulation and the impedance caused by the connectors. Insertion loss is usually expressed in decibels dB with a minus sign. Insertion loss increases with distance and frequency.
Return Loss
Return Loss is the measurement (in dB) of the amount of signal that is reflected back toward the transmitter. The reflection of the signal is caused by the variations of impedance in the connectors and cable and is usually attributed to a poorly terminated wire. The greater the variation in impedance, the greater the return loss reading.
If 3 pairs of wire pass by a substantial amount, but the 4 pair barely passes, it usually is an indication of a bad crimp or bad connection at the RJ45 plug. Return loss is usually not significant in the loss of a signal, but rather signal jitter.
Near-End Crosstalk (NEXT)
Near-End Crosstalk (NEXT) is an error condition that describes the occurrence of a signal from one wire pair radiating to and interfering with the signal of another wire pair. It is the difference in amplitude (in dB) between a transmitted signal and the crosstalk received on other cable pairs at the same end of the cabling.
Power Sum NEXT (PSNEXT)
Power Sum NEXT (NEXT) is the sum of NEXT values from 3 wire pairs as they affect the other wire pair. The combined effect of NEXT can be very detrimental to the signal.
The Equal-Level Far-End Crosstalk (ELFEXT)
The Equal-Level Far-End Crosstalk (ELFEXT) test measures Far-End Crosstalk (FEXT). FEXT is very similar to NEXT, but happens at the receiver side of the connection. Due to attenuation on the line, the signal causing the crosstalk diminishes as it gets further away from the transmitter. Because of this, FEXT is usually less detrimental to a signal than NEXT, but still important nonetheless. Recently the designation was changed from ELFEXT to ACR-F (far end ACR).
Power Sum ELFEXT (PSELFEXT)
Power Sum ELFEXT (PSELFEXT) is the sum of FEXT values from 3 wire pairs as they affect the other wire pair, minus the insertion loss of the channel. Recently the designation was changed from PSELFEXT to PSACR-F (far end ACR).
Attenuation-to-Crosstalk ratio (ACR)
Attenuation-to-Crosstalk ratio (ACR) is the difference between the signal attenuation produced NEXT and is measured in decibels (dB). The ACR indicates how much stronger the attenuated signal is than the crosstalk at the destination (receiving) end of a communications circuit. The ACR figure must be at least several decibels for proper performance. If the ACR is not large enough, errors will be frequent. In many cases, even a small improvement in ACR can cause a dramatic reduction in the bit error rate. Sometimes it may be necessary to switch from un-shielded twisted pair (UTP) cable to shielded twisted pair (STP) in order to increase the ACR.
Power Sum ACR (PSACR)
Power Sum ACR (PSACR) done in the same way as ACR, but using the PSNEXT value in the calculation rather than NEXT.
DC Loop Resistance
DC Loop Resistance measures the total resistance through one wire pair looped at one end of the connection. This will increase with the length of the cable. DC resistance usually has less effect on a signal than insertion loss, but plays a major role if power over Ethernet is required. Also measured in ohms as the characteristic impedance of the cable, which is independent of the cable length.
What this clearly demonstrates is that most people can knock up a Ethernet Cable however, if you need it to work to the full speed and functionality you must test to the correct standards.
Many slow networks have been identified by their poorly made cables so it’s an important part of the network to get right. Which is why really only highly skilled well trained technicians should make the cable since they are probably the only people that will have the proper network analyzers for the job.
New Guide to Ethernet Cat 5e & Cat 6 Testing Part II!
In our previous Guide to Cat 5e & Cat 6 Cables we discussed the main differences and briefly showed the complex test structure required for true full Ethernet connectivity.
This week we are going to go into much more detail. Lets look at why the testing is so complex and why it is important that correct testing is carried out.
Firstly, the Copper conductors used to carry the data signals are being stretched to their limit and to achieve the required speeds every effort is made in the construction to make sure the best data flow is reached.
For example did you know that each of the four twisted pairs are twisted at different tightness? This ensures the very best data transmission rates with lowest crosstalk and signal loss. it’s small details like this that makes the copper conductors work to such high performance levels.
Now let;s look in detail at each test criteria. To be sure that the cable link preforms to the required standard it must meet the full 9 tests which can only be carried out by Network Analyzer.
The following is the full list of required tests:
Insertion Loss
Insertion loss, also referred to as attenuation, refers to the loss of signal strength at the far end of a line compared to the signal that was introduced into the line.
This loss is due to the electrical impedance of the copper cable, the loss of energy through the cable insulation and the impedance caused by the connectors. Insertion loss is usually expressed in decibels dB with a minus sign. Insertion loss increases with distance and frequency.
Return Loss
Return Loss is the measurement (in dB) of the amount of signal that is reflected back toward the transmitter. The reflection of the signal is caused by the variations of impedance in the connectors and cable and is usually attributed to a poorly terminated wire. The greater the variation in impedance, the greater the return loss reading.
If 3 pairs of wire pass by a substantial amount, but the 4 pair barely passes, it usually is an indication of a bad crimp or bad connection at the RJ45 plug. Return loss is usually not significant in the loss of a signal, but rather signal jitter.
Near-End Crosstalk (NEXT)
Near-End Crosstalk (NEXT) is an error condition that describes the occurrence of a signal from one wire pair radiating to and interfering with the signal of another wire pair. It is the difference in amplitude (in dB) between a transmitted signal and the crosstalk received on other cable pairs at the same end of the cabling.
Power Sum NEXT (PSNEXT)
Power Sum NEXT (NEXT) is the sum of NEXT values from 3 wire pairs as they affect the other wire pair. The combined effect of NEXT can be very detrimental to the signal.
The Equal-Level Far-End Crosstalk (ELFEXT)
The Equal-Level Far-End Crosstalk (ELFEXT) test measures Far-End Crosstalk (FEXT). FEXT is very similar to NEXT, but happens at the receiver side of the connection. Due to attenuation on the line, the signal causing the crosstalk diminishes as it gets further away from the transmitter. Because of this, FEXT is usually less detrimental to a signal than NEXT, but still important nonetheless. Recently the designation was changed from ELFEXT to ACR-F (far end ACR).
Power Sum ELFEXT (PSELFEXT)
Power Sum ELFEXT (PSELFEXT) is the sum of FEXT values from 3 wire pairs as they affect the other wire pair, minus the insertion loss of the channel. Recently the designation was changed from PSELFEXT to PSACR-F (far end ACR).
Attenuation-to-Crosstalk ratio (ACR)
Attenuation-to-Crosstalk ratio (ACR) is the difference between the signal attenuation produced NEXT and is measured in decibels (dB). The ACR indicates how much stronger the attenuated signal is than the crosstalk at the destination (receiving) end of a communications circuit. The ACR figure must be at least several decibels for proper performance. If the ACR is not large enough, errors will be frequent. In many cases, even a small improvement in ACR can cause a dramatic reduction in the bit error rate. Sometimes it may be necessary to switch from un-shielded twisted pair (UTP) cable to shielded twisted pair (STP) in order to increase the ACR.
Power Sum ACR (PSACR)
Power Sum ACR (PSACR) done in the same way as ACR, but using the PSNEXT value in the calculation rather than NEXT.
DC Loop Resistance
DC Loop Resistance measures the total resistance through one wire pair looped at one end of the connection. This will increase with the length of the cable. DC resistance usually has less effect on a signal than insertion loss, but plays a major role if power over Ethernet is required. Also measured in ohms as the characteristic impedance of the cable, which is independent of the cable length.
What this clearly demonstrates is that most people can knock up a Ethernet Cable however, if you need it to work to the full speed and functionality you must test to the correct standards.
Many slow networks have been identified by their poorly made cables so it’s an important part of the network to get right. Which is why really only highly skilled well trained technicians should make the cable since they are probably the only people that will have the proper network analyzers for the job.
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