This part of IEC 60728 deals with the transparent return path of cable networks operated in the frequency range between 5 MHz and 65 MHz or parts thereof. Higher frequencies may be used in fibre based networks.
NOTE In addition, it is possible to use the frequency range from 0 MHz to 5 MHz for return path transmissions, for example for NMS or other control, monitoring and signalling purposes. Applications below 5 MHz are not covered by this standard.
An active return path carries typically only return signals. A passive return path can be used for both return and forward signals.
This standard lays down the basic methods of measurement for signals typically used in the return path of cable networks in order to assess the performance of those signals and their performance limits.
All requirements refer to the performance limits, which shall be obtained between the reference points (Figure 1) of the return path system.
One reference point is the network termination close to the subscriber. It is the last point where all forward and return signals are present and carried on the same cable. If no network termination point exists, the reference point is the system outlet.
The other reference point is the input of the return signal receiver (or transceiver). At this point, the transparent signal path ends and beyond this point, the signal is treated in a non-transparent way. The return signal receiver can be situated at the headend but can also be at the node of the coaxial cell or at any other point of the network.
In addition to the system performance requirements for the transparent return path, system performance recommendations were laid down in this standard, for example for the overall frequency allocation, for the use of specific modulation techniques for different interactive multimedia services or for different sub-bands within the return path frequency range, etc.
Specific equipment installed in cable networks for the operation of such return paths is standardised in the relevant equipment standards, parts 3 to 6 of the IEC 60728 series.
Transmission systems are not within the scope of this standard.