21581 - SCTE Broadband August2022 COMPLETE v1

87 Vol. 44 No. 3 - September 2022 Issue from the archive (2) the losses which occur and problems of making tap- offs, particularly if a tree distribution network is attempted (3) losses occurring at bends - which can be made minimal in practice Because of these problems it is concluded that an optical fibre analogue of a co -axial cable tree network is not a practical or economic proposition. A switched-star network appears to be a better solution i.e. using one (or two) optical fibres per subscriber. Such a network would have a minimum of joints and no tap-offs. Amplifiers would not normally be used in town distribution i.e. up to 3 or even 5km. Techniques for handling bunches of fibres and cables in and out of ducts along streets, homes, etc need developing. With a switched network a wide band TV capability is not required i.e. only one or two TV channels are needed at any one time but a return communication capability is required to operate the centralised switching. However, 'scrambling' for security is not required - a saving with switched systems. In order to avoid the added cost of analogue to digital processing and the reverse, LED devices can be used for signal launching with intensity modulation. These devices are not only cheaper but more reliable than lasers. Large scale experiments with networks on these lines have been and are being satisfactorily carried out in various parts of the world, but initial cost indications are higher than co-axial networks. I am attempting to obtain better forecasts for large scale production as it is vital to obtain such information before the country is committed to billions of L's expenditure in a 'national' network. As I said earlier if distribution over fibres is not economic there is no doubt that the application, as per British Telecom to wideband trunks is and we may see a combination of fibre trunks/links and ordinary co-axial cable for distribution making up future networks. TV Receivers for Cable Several set manufacturers in the USA make receivers which are known as 'cable ready'. In general these receivers have additional interband VHF channel coverage and extended coverage to some 250MHz. The adjacent channel rejection performance is adequate and cross modulation effects in tuners are minimal. Direct signal pickup into antenna inputs is minimised by good screening and matching. Because of the small demand in the UK very little attempt has so far been made to make suitable receivers but some steps in the right direction have come about with the introduction of surface wave IF filters. Cable operators of co-axial systems in the UK have overcome the inadequate coverage of receivers by using convertors; a rather expensive alternative. The channel spacing on cable has also been set higher to avoid adjacent channel operation interference - which means fewer channels than possible with good receivers. Most convertors include a descrambling section for the Subscription TV channel(s). However, if receivers covered the cable channels the descrambling arrangement could be a more compact wall-mounted affair only available to Subscription channel subscribers. An advantage of receivers with full channel coverage is that the very desirable remote control circuits can be built in, whereas the cable convertor box has to be wire- connected and also needs a mains supply cable. With the increased popularity of cable in Europe, we shall probably see an increase in supply of suitable receivers. Of course, in the event of using a switched network receivers will only need one input channel. Discussion Mr. D. W. Heightman: Perhaps I could ask Mr. Fabich a question to start the discussion. This relates to why you were putting in optical fibre links in place of the microwave. Was this because of reliability, or because of the cost? Mr. W. Fabich: That is a question which is actually decided by our PIT. Normally the frequencies in densely populated areas are occupied by other services and they tend to run out of frequencies. So the first ones they push out of the air are those who are not strong enough to say: "We have to stay in." The PTT decided that they would have a temporary solution for six to seven ye ar s with microwave and that after that they would make cable systems. Now, we are not opposing that, because we will take out one microwave and then the next one, and we shall start gaining experience with optical fibres in trunk connections. However, when starting cable TV it is obvious that microwave is the quickest solution, because when you think how long it takes to lay a cable of eight or ten kilometres, with microwave it only takes four weeks. It is not only a question of economics with us, but a question of becoming acquainted with new technologies. I am sure that microwave with a trunk of 10 to 12 kilometres is cheaper than an optical fibre connection. Mr. S. Kharbanda /Labgear Ltd.): I noticed on of the diagrams that Mr. Fabich displayed that elements of the system showed a two-way capability. My first question is this: Is the two- way capability being used at the moment and, if so, for what purpose? Mr. Fabich: We have a double cable system, with two cables transporting nine TV channels. It is a VHF system, with a return path possibility. We have plugged in all our amplifiers to the return module. So we have a return channel from 5 to 25MHz. It goes from the headends to the conversion stations. At the present time there are 60 conversion stations in Vienna, and when we finalise our system in 1985/86 there will be 150. At the moment there is neither supervision nor anything else, but our idea is that in the future there might be local events taken up by TV cameras, brought back to the centre and then distributed via the main TV network. Financially it is good, because people are already temporarily renting these free frequency bandwidths for data transmission and TV transmission. We rent it to anybody who would like it, but it is only in that part of the network that it is two-way. Mr. Kharbanda: Secondly, is there any form of pay television mooted for your country. I believe that there is no pay television at the moment. Do you know whether you will have pay television in Austria within the next five years? Mr. Fabich: In the next five years, yes: in the next three years, no. In Austria the law is that broadcasting is only allowed to be done by the State-controlled broadcasting company, ORF, which has the monopoly. So at the moment you start with local programmes and community programmes. In fact even the city of Vienna is not allowed to make its own programmes, and that is the law. It really depends on the political scene and what will happen in the next elections in 1983. In our country and maybe in your country, too, cable TV is a very political item. Both the ruling Socialist Party and the Conservative Opposition Party are in favour of local programmes if they can gain anything from that move, but it will take another three years at least. Mr. Kharbanda: My last question is a technical one. Could you tell me, please. whether in Austria the West German FTZ regulations concerning radiation leakage are mandatory? Do you have to have equipment which meets the West German FTZ regulations, as far as radiation leakage is concerned? Vol. 12 No. 1 August 1982 31