re The main problem for the cable operator is to know which new than 1/2 imp. Most parameters must therefore fall well below the format will be widely implemented, and when to plan for the extra 1/8th imp value, but according to the nature of the network it may capability. be sensible to let some produce more impairment than others e.g. K-rating and single frequency interference might be allowed to be relatively high. 57.3.7.3 Conditional access The signal inputting to the network, perhaps received off air, will itself be already impaired, and this will contribute to the ultimate Improved techniques will be sought here, particularly with pay per impairment at the end of the network. For concatenated links like view in mind. Switching is one answer; another is interdiction this some parameters will add up predictably (e.g. signal/noise (spoiling all but the wanted signal) rather than scrambling. ratio), whilst others will not and indeed could even improve if opposite trends occur on the links. Individual measurement techniques exist for each parameter, but 57.3.7.4 Fibre optic enhancement nowadays automatic measurement equipment is available, which, though not cheap, will provide a read out of a large range of these. This made some impact a few years ago with multi channel FM An associated test signal generator provides the source to input to links in the super trunk, and now with significant interest in digital the network or equipment under test. However most broadcast operation there. More recently the practicality of AM multiplexes channels also include the test signals in their vertical blanking over fibre has excited enormous interest. The prospect of replacing period, allowing the total degradation to that channel to be assessed. the large chains of coaxial cable amplifiers allows both improved The above measurements relate to the baseband video signal, on performance (which in many existing systems has been decidely sub which a full analysis of impairments can be carried out. However standard) and more cha