21581 - SCTE Broadband August2022 COMPLETE v1

84 Vol. 44 No. 3 - September 2022 Issue from the archive Although we hear a great deal about special and 2-way services, apart from a very few cases the foregoing summarises what cable offers currently in the US. In the West Coast area, Viacom last year became the first company to offer a home security system at about one half the cost of a traditional system - available to some 30,000 homes in one district. Most of the so-called "interactive" facilities are still "in the future". This is with the notable exception of the 'Qube' interactive system run by Warner Communications, in Columbus Ohio as a large scale experiment. The system is engineered on the latest 2-way cable basis, outward 40-300MHz 30 channels return 5-30MHz. Data is picked up from each subscriber in digital form, returned to the 'exchange' either (a) by the subscriber pressing one of the 5 buttons or (b) by a self-generated signal indicating to which channel 'sub' is tuned. The service requires a rather large and secure box within each home, in addition to the wire -connected programme selector unit for subscriber use. Externally also additional digital units, injecting into the main co-axial line amplifiers are mounted on poles etc. The service also gives central indications of the location of any failure on the system. The total cost is probably twice that of simple co -axial systems. In addition to basic cable service, there is first a premium service, paid by monthly subscription, and then a third level of pay-per-programme. For the latter the price varies from say $2.50 upwards centrally recorded/billed. Some channels also provide a data service similar to Teletext. Such services can also be seen on several other town systems, often used for small 'ads' - local advertising. From Table 1. it will be seen that there is an increasing number of systems offering public, government and educational services. The percentages in brackets represent the increase over the previous year. Technical Features and Standards The co-axial multi-channel VHF system in various forms is universal in the USA, i.e. there is virtually no HF multi-pair. Thus a great deal of standardisation and cost reduction can take place. Some of the older systems of, say, 10 years of age use rather inferior cables and amplifiers than are now generally being installed. These older systems are, in many cases, being progressively re-cabled to modern standards. There is now virtual standardisation on cables used. In many cases the outer conductor, of aluminium alloy tube, is exposed i.e. not PVC coated. On trunk lines cable diameters of the order of 1" are often used. These are 'air- filled'. Most new systems are being installed with 2 cables for outward and return signal paths. The dual-purpose amplifier housings for these cables have plug-in amplifier modules and currently systems are being installed without the return path amplifiers in position. Thus conversion to 2-way could be made at a later date at some further expenditure but avoiding additional cable erection costs. The continuous VHF spectrum from 50-250+MHz is used for outgoing signals and 5-30MHz for return signals (when or if required). Into this spectrum provision is made for 30 NTSC TV channels (6MHz wide) and a few companies go up to 36 channels. Qube are talking of going to 50 channels by extending above 250MHz. Amplifiers for use with these systems are of modern solid state design, using push-pull circuits to avoid cross modulation problems. Cables, amplifiers and other equipment are all carried on public utility poles, e.g. power and telephone. A galvanised steel stranded wire stretched between poles normally carries the cable and other equipment—this is called the "strand". In some cases cable is run underground and with the use of modern cable laying machines and cables, costs are being reduced so that underground is not so much more expensive than overhead. The local situation very much decides the approach taken e.g. with soft road edges or behind homes in soft ground, cable laying underground is relatively cheap. With underground systems compact metal kiosks are used for amplifiers etc. at ground level, similar to UK practice. Security aspects, i.e. the exclusion of subscribers only paying for basic cable service from receiving the Pay channel(s) is most frequently taken care of by the switched convertor used to transfer signals from the cable to the TV receiver. The TV receiver is left tuned to one VHF channel and channel selection is made on the convertor to the set, not remotely controlled. An alternative system is the use of simple traps which attenuate the vision carriers of the Pay channel(s) so as to spoil reception. These traps are mounted outside the home out of reach and are shorted out for Pay subscribers. Of the more sophisticated systems, the square wave sync. suppression 'scrambling' is most frequently used. Several set makers now make 'cable ready' receivers. Satellite ground station antenna dishes are firmly concrete block mounted on open ground unobstructed by objects such as trees, traffic, wire fences etc. The angle of reception - towards the equator, is quite acute, say 30° in most latitudes. The US satellites operate in the 4GHz region. A typical 5-metre diameter dish antenna costs about $12,000 and the complete installation, with frequency conversion (mounted at rear of antenna) to normal TV frequencies, taken by co-axial cable to the headend site about $20,000. For good reception of normal off-air signals efforts are made to have aerials on hill tops with high masts and in open interference-free areas. Micro-wave links are very frequently used to couple these signals to distribution equipment in towns. The FCC regulate Technical Standards and obligatory performance tests to which systems must comply. This performance is subject to annual FCC inspection. Special regulations apply to operation on channels outside normal off-air frequencies i.e. to avoid cable radiation interfering with other services. The regulations are too lengthy for me to make other than this brief reference. 28 Cable Television Engineering