IEEE Std 802.3cg™-2019 standard specifies a balanced pair of conductors. It does not require twisting of the conductors, nor does it require shielding. Instead, it defines the characteristics for a mixing segment. This section shows characteristics for 4 different cables which will be used later in this application note, and compares them to the standard.
High quality single twisted pair with shield. Details available under request.
Single twisted pair cable. This particular cable is often used in Microchip demonstrations and trainings.
Single twisted pair from a standard CAT6 cable.
Low quality, single pair cable, no twists.
15 meter lengths were not available for all of the cables, so the characteristics were measured over 5 meters to create models which were then applied to a simulation tool. All simulations shown in this application note were generated using this same tool, and later sections will show that this tool corresponds very closely to actual measurements. Details of the simulation are available upon request.
Equation 4-1. Insertion Loss
Insertion loss for the 4 cables above, along with the IEEE limit is shown in Figure 4-1. All but cable 4 meet the requirement across all frequencies.
Figure 4-1. Insertion Loss for Different CablesEquation 4-2. Return Loss
The return loss for the 4 cables above is compared with the IEEE limit is shown in Figure 4-2
Figure 4-2. Return Loss for Different Cables
Equation 4-3. Mode Conversion Loss
Figure 4-3 shows the mode conversion loss and IEEE limits for the 4 cables. Note that only cable 3 meets this standard at all poins.Figure 4-3. Mode Conversion Loss for Different Cables
These are the characteristics that must be met at each node on the segment to ensure that compliant nodes will always work. Of course, compliant nodes may work on segments that do not meet these characteristics, but operation is not guaranteed.
