21581 - SCTE Broadband August2022 COMPLETE v1

89 Vol. 44 No. 3 - September 2022 Issue from the archive is so smallscale that it is very difficult to get statistics. There are only about four or five areas where this has taken place and I think it is a bit of a dead duck, as far as I can make out. It is a different situation to what may come along when the BBC and possibly IBA have coverage of the whole of the UK on one satellite. Mr. Fabich: In the States, when we speak of subscription TV, you must also bear in mind that it is the code from a terrestrial transmitter and it is coded by the broad-casting transmitter. Mr. Heightman: I am sorry, I thought you were referring to the satellite. In fact that is almost negligible and it is certainly not moving in relation to cable in any area. Mr. A Wells (Telephone Cables Ltd.): You have implied that you would like to see fibres in the star network to subscribers as opposed to cable. Provided the economics can be got right and the price of the fibres can be made more reasonable, I would like your view as to why you believe fibres offer advantages in this area? Mr. Heightman: Well, the simple advantages are well-known. Other than the possibility of the mechanical handling aspect, there is the relative light weight, compactness and freedom from electrical radiation problems, which are increasing so far as cable is concerned. The engineering, screening, and so on, which is necessary on co-axial systems or any cable system is quite rigid if you are to comply with the regulations. In the longer term it is very probable that the material costs of optical compared with copper cable could be considerably less with large-scale manufacture. These are quite simple advantages and there nothing very scientific about it. Because of the difficulty in working in field conditions with fibres, one sees the need to go for a star network, rather than the impossible technical problem of a tree network, except for linking large areas - for trunk purposes, or links in place of microwave. Mr. Wells: Do the problems of interference outweigh the advantages? Mr. Heightman: Probably, yes. Mr. Fabich: I always have problems increasing the bandwidth in glass fibre in comparison with co-axial cable. Mr. Heightman: It depends to what kind of glass fibre you are referring. Mr. Fabich,: We are discussing glass fibre to the subscriber. It should be a good one, but it must be low cost, because it will go to millions of homes. A co-axial cable has a bandwidth of I GHz and goes from 60 Hz right up to 800 or 900 MHz without any difficulties. You have to compare that with the optical fibre. Is it practical, not economical, to have a star-shaped network? If we agree on that, then we obviously come to the optical solution. Mr. Heightman: Could I say that one does have to bear in mind that when the question of security crops up, again a switched network makes that very much more simple, because you are not involved in scrambling as you have an individual cable going to every home. Mr. Fabich: In our system, if there is a large apartment house all the cables go down to the cellar and you have a box down there with all the outlets. For safety, for tapping reasons and for serviceability such a star point is very nice. Because they have that philosophy the PTT are always in favour of a star network. Then the industry started to think about loops, which everybody uses today, such as in data transmissions and in-house networks, but that is something unheard of by the PTT. For them that is impossible - every subscriber must get his copper cable from their star! It has its advantages, but it costs a lot of money and I cannot see the private investor investing in such networks. It can only be done out of the revenue of the PTT and the telephone service, because it takes 80 or 90 years to have all the homes connected. Mr. L. T. Mudd (Rediffusion Engineering): It is probably covered in his paper, but I would like to ask what Mr. Heightman thinks of the differences that exist between the situation here and the situation in the USA, and the wisdom of trying to transport a distribution technique across the Atlantic? In the USA the VHF bands are used for terrestrial television. Here I should think there must be at least six people using them at the moment to receive 405-line transmissions. We are going to lose a little of Band I to mobile radio shortly, but what the fate of the rest of Band I is, I do not know. The takeover could extend to Band 3 and we could have the Gas Board, British Telecom, or somebody radiating like crazy in a bit of the spectrum which is a vital part of the US type of system. Secondly, in the US they do not need safety isolation in the co-axial feed to the receiver so that they do not have a capacitor on the inner or the outer. On the Continent there is a capacitor on the inner and the outer has to be earthed, as it does in the States. As far as I know, only we and South Africa are silly enough to put a capacitor on the outer conductor. Even if that capacitor is made truly co-axial, which has advantages, you are still in trouble with immunity. At the point where your signal is lowest, that is, at the subscriber, that is the very point where you might find the Gas Board van outside radiating and it is also the very point where you have to have cheap cable, as Mr. Fabich has pointed out. So with those differences in mind, Mr. Heightman, would you advocate copying an American VHF type system in this country for 30 channels? Mr. Heightman: I would not call that a 64,000 dollar question, but it is at least 32,000! I would go as far as saying that if it cannot be extended upwards above the normal VHF to 300 or possibly even 400MHz, then we have got to have serious thoughts about what system we are going to use. To go into the UHF band with its attendant greater losses in cable, particularly, is practical on short distance distribution possibly, but as an overall network we are going to put up the cost of the co-axial system quite considerably if we shift up very much higher. On the other hand, the work we have done does show that the systems themselves can be kept down to the required limits of unwanted pickup by good engineering practice. You quoted the front end of the receiver and particularly the co-axial antenna terminal and its isolation. Work has been done by various people in an effort to reduce this problem. I must admit that I am not right up-to-date on what level of protection there is, but I believe that some tests have shown that the modern is satisfactory. I do not know receiver whether anybody could help me on that point. Certainly I would say that it is something we ought to straighten out on the receiver, rather like other aspects, such as adjacent channel rejection, cross-modulation and so on, which will be necessary if we are going to get anything like 30 channels on VHF, which is the sort of number required. Our solution in the interim is a converter, which has all the desirable characteristics, ahead of the receiver, but it still does not necessarily stop the receiver picking up some unwanted radiation if it has a bad co-axial input. I think I can summarise by saying that have to adopt pretty well a duplicate of the USA, but in UK terms with 8MHz channels, or something very different, and this is a job for the technical committee. The President: I must now close the meeting. Time has been very much against us, but on your behalf I would like to thank our speakers for their excellent papers. Let us hope that, before long, cable television activity in this country is just as extensive as elsewhere in the world. Please join me in showing our appreciation to the speakers in the usual way. (Applause) Discussion at the Northern presentation at the Mercury Motor Inn, Ainley Top, Huddersfield, on 7th April 1982, with Mr. W. Beesley in the Chair. Mr. John Sunderland (Rediffusion York- shire) enquired how franchises for cable systems were awarded in Austria. Mr. Fabich replied that the local councils placed the franchise on open tender. Interested companies must be prepared to totally finance the venture and accept the councils' decision in respect of choice of programmes distributed. It is usually the case that the Company submitting the proposed lowest subscriber input charge is awarded the franchise. Mr. D. Coomber (Gould Instruments) commented that he was of the opinion that the SCTE should be making recommendations to the Government as to the type of cable networks to be used in future national developments. Mr. Heightman was in full agreement and made the point that Fellows and Members of the Society were currently involved with their Companies on this very matter. Mr. R. G. Betts (Sapperstein & Assoc.) referring to Mr. Heightman's paper in respect of Interactive Channels, stated that his Company had experienced problems and loss of data due to insufficient/ineffective coax cable screening. Mr. N. McDonald (Raydex International) taking up this point said that cables with sufficient isolation could easily be produced. providing the user was prepared to pay. Mr. Fabich stated that in his opinion it was false economy to install inferior cable when labour constituted the greater percentage of installation costs. In Austria financiers of cable systems were happy to bury their money, i.e. copper taped cables underground, secure in the knowledge they were the best money could buy, and would not require exhuming. Binders and Index for SCTE Journal Vol. 11 This issue of the SCTE Journal includes a pull- out Index (centre pages) for Vol. 11 Nos. 1-10 (February 1978-February 1982). Binders to hold 10 copies of the Journal are being prepared and will shortly be available from the Secretary at £5 each, including postage. Payment with order is essential . Vol. 12 No. 1 August 1982 33