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THE WAY I SEE IT By NEVILLE WILLIAMS Is UHF TV really as good as it's cracked up to be? Having in mind the heat that was generated when plans were first announced to re-deploy Australian TV services into the UHF band, the actual implementation appears to be progressing almost routinely. Are the problems less serious than some anticipated or is it that we have yet to come to grips with reality? Like many other Sydney viewers, I went through the exercise, some time ago, of reorganising my reception of SBS from VHF channel O to UHF channel 28. Perhaps because of a latent streak of "she'll be right, mate", the procedure proved to be a rather messy example of: "do as I say, not as I do"! But more about that later. I'm prompted to discuss the subject here by reason of a short letter from one of our readers, which reads as follows: Dear Neville, I have been told that UHF reception is potentially better than VHF reception although, on virtually every occasion I have seen SBS on channel 28, it has been nowhere near as good as the best reception I have come to expect on VHF. Could you throw more light on this whole question? Is UHF supposed to be as good as VHF and if not, why not? R.D. (Box Hill, Vic.) When publisher Leo Simpson rang to tell me that a copy of the letter was on the way to me, what began as a brief conversation developed into a full-scale review of the events that led to the present 12 SILICON CHIP situation and the implications for SILICON CHIP readers over the next couple of years. So R.D's request to "throw more light" on the subject is timely. I'll therefore set about describing how, when, where and why! In the mid '50s, the guidelines adopted for Australian TV broadcasting seemed enterprising enough for our particular situation. Australia would use the new 625-line CCIR System-B video standard - the first country to do so and would set aside ten clear channels in the VHF spectrum (30-300MHz). They would hopefully accommodate three stations in the capital cities and two stations in strategic provincial centres across the nation. VHF technology was proven and predictable, and the equipment clearly within the capacity of local industry to adapt, make, install and service. What was not forseen was the enormous penetration rate, unique by world standards, which peaked at 430,000 new TV receivers in 1959/60. In its wake came public and commercial pressure for additional TV services resulting, in 1961, in a decision based on the industry-inspired Huxley Committee Report, to increase the number of VHF channels from 10 to 13. The proposal involved shuffling those not already occupied by major stations (see list) and re-locating TV channels 3, 4 and 5 within the commonly recognised international FM band (88-108MHz). Who needed FM broadcasting? The move had widespread support at the time, because loss of the FM band - then sparsely used in Australia - seemed a modest price to pay to perpetuate the technical convenience of an all-VHF TV system. Moreover, AM radio was itself in total eclipse and AM station operators were not about to mourn the setting aside of a potentially competitive system! By way of concession, it was agreed that if and when an FM radio service was required, it could be technically up-graded (to advantage) and accommodated in the sparsely populated UHF spectrum (300-3000MHz). Besides (sotto voce) it would be rather nice, in that event, if Australian receiver manufacturers had the Australian FM market to themselves by reason of unique frequency and system standards! But like the modern-day "greenies", a small pro-FM lobby was vocal and tenacious in canvassing the merits of stereo FM broadcasting, and in getting across the point that Australian broadcasters and listeners alike would be severely disadvantaged if we sought to establish an FM service out of step with the rest of the world. My views at the time were summarised in the April 1962 issue of "Radio TV & Hobbies", in a trenchant criticism of the ABCB (Australian Broadcasting Control Board) and the "smokescreen" being created by the TV industry to cloud the issue. And cloud it they did. with all but a few supreme optimists reluctantly resigned to Huxley's fait accompli. But in 1974, following the recommendations of an inquiry chaired by Sir Francis McLean, the Federal Government reversed the 1961 decision, authorising restoration of the FM band and progressive redeployment of the TV service into the UHF spectrum. So in September 1974, a surprised and delighted Music Broadcasting Society was invited to apply for licences and within a few months, was on the air with 2MBS in Sydney and 3MBS in Melbourne. A new era had begun. There is room for speculation as to why the Whitlam Government appeared so partial to VHF FM but technical evidence and revisionist policy apart, it certainly complemented the earlier decision (1972) to reduce artificial protection of the local electronics industry. Tariffs had gone and now so had the notion of uniquely Australian FM receivers. As it turned out, the market was soon flooded with imported AM/FM tuners and receivers and largely as a result, FM broadcasting has since emerged as a major competitor for AM. A dual VHF /UHF TV system A provision in the 197 4 decision was that receivers for colour television, which was scheduled to begin in the following year, should include facilities for UHF reception. This requirement later became applicable to VCRs too. At the time, it looked almost like a "sticking plaster" clause but so far normal re-equipment with colour receivers and VCRs seems largely to have kept pace with the installation of UHF transmitters and translators. Theoretically, most viewers are now in a position lo take advantage of UHF TV transmissions if and AUSTRALIAN TELEVISION CHANNELS ORIGINAL PLAN 13-CHANNEL PLAN (1961) Channel Number Frequency (MHz) Channel Number 1 5 49-56 63-70 85-92 132-139 139-146 6 7 8 9 10 174-181 181-188 188-195 195-202 209-216 1 2 3 4 5 5A 6 7 8 9 10 11 2 3 4 o Frequency (MHz) 45-52 (a) 56-63 63-70 85-92 (b) 94-101 (b) 101-108 (b) 137-144 (c) 17 4-181 181-188 188-195 195-202 208-215 215-222 NOTES: (a) Mainly used for translators and RF input to TV receivers from VCRs, &c. Long-term use for major transmitters under review but doubtful. (b) To be ultimately cleared nationwide to make room for VHF FM sound broadcasting. (c) Used mainly for translators. Continued use for major transmitters still under consideration. when they have to but, as we shall see later, there is more to it than simply pushing a different button. In case you aren't familiar with the basic figures, Australian TV transmissions each occupy a nominal bandwidth of 7MHz, as compared with about 200kHz for an FM-stereo sound transmission. For this reason, TV channels can only be accommodated in the very-high and ultra-high frequency bands (VHF and UHF) or at still higher frequencies, as for satellite technology. Having in mind the number of services that have to be accommodated nowadays, the amount of spectrum space which can be conveniently allocated for TV channels is severely restricted in the VHF sector and by no means unlimited even at UHF. Hence the hassle. Well then, what are the advantages and limitations of the VHF and UHF bands and how do they affect ordinary viewers? Pros and cons of VHF TV VHF TV signals are best received with actual or near line-of-sight conditions involving a tall. wellsited lrnnsmitting tower and (ideal- ly) an elevated outdoor rece1vmg antenna with a clear path towards the transmitter. In practice though, VHF TV signals are subject to a fair amount of refraction and reflection, which often allows them to be received at a "watchable" level over a considerable distance (100km or more), or in the lee of rolling hills, or in other ostensibly "shadowed" situations. While this is a bonus for viewers in problem areas, reception can still be compromised by the fact that the low-end channels in particular (0, 1 & 2) are vulnerable to interference from car ignition systems and electrical appliances, and from arcing across dusty highvoltage insulators. Thunderstorms also cause considerable interference. The weaker the signal, the more noticeable the effect on the picture. Again. the same low-end VHF transmissions are sensitive to transitory atmospheric disturbances (eg, sporadic-E ionisation and meteor showers) which can produce "anomalous" propagation, with the signal being received hunMA Y 1988 13 A good antenna is essential for noise-free UHF reception. Shown above are the TC-10 and TC-18 UHF antennas from Hills Industries. dreds of kilometres away, perhaps in areas where another station is operating on the same channel. The resulting risk of mutual interference limits the number of geographically isolated stations which can share the low-end channels, in particular. At the receiving end Within the normal service area, a VHF receiving antenna can usually be a fairly simple configuration with 7 or 8 elements, connected to the set via 70-ohm coax or 300-ohm ribbon. Not highly directional, such antennas do not need to be lined up on the station with pinpoint accuracy. But, equally, they provide only limited discrimination against "ghosting", caused by reflections from prominences or large buildings on either side of the transmission path or from beyond the receiving site. By reason of the long elements (up to three metres or so) bird and wind damage can be a problem, as evidenced the the recent fate of a neighbour's VHF antenna. Prominently placed to "see over" my own home, it is hardly a thing of beauty but it must have proved attractive to a passing flight of galahs, which chose to settle one by one, on the reflector element. Under their combined weight, I watched the rod sag and finally break, spilling birds in all directions! The interesting thing is that this very antenna is still in use, along 14 SILICON CHIP with any number of other aged and bedraggled antennas in the area, all presumably still pulling in pictures. Indeed, many viewers in the capital cities may well be wondering what the fuss is all about. They have a reasonable choice of programs and with a little effort, galahs notwithstanding, most of them receive reasonable pictures. Even the lazy ones seem to manage in most suburbs, so why do we need a new system? (You could argue about what constitutes a reasonable picture but that is a story for another day). The reality is that there are simply not enough VHF channel options to cater adequately for problem urban areas, such as the coastal fringe of Sydney, let alone provincial centres and smaller pockets of population. Whether 10 channels or 13, substantial re-deployment into UHF is a necessity, not an option. (See the Publisher's Letter, January issue). How does UHF compare? In Australia, in the UHF band, there is space for many more channels (currently 39) than on VHF (probably about 10). As well, UHF signals are not prone to random or anomalous propagation, so that frequencies can be used over and over again across the continent. with little risk of co-channel interference. The fact that the frequencies are higher and the wavelengths smaller makes it easier to design transmitting antennas with well-defined directional characteristics and a higher effective gain or ERP (effective radiated power) towards the service area. It all adds up to the possibility ot many more TV transmitters than would be possible on the VHF channels, including a multiplicity of lowpower community stations and very low power translators. The higher ERP is also a potential bonus, with SBS channel 28 in Sydney, for example, radiating an effective 300kW, compared with lO0kW from ABN-2 on the same tower. This means stronger signals in the service area although signals elsewhere may be weaker, because there is less tendency for UHF to be refracted around or over hills or other obstructions There is a plus factor in that UHF signals are substantially immune to interference from power lines, mains appliances and automotive ignition. In very strong signal areas, viewers sometimes report use able UHF signals from existing VHF antennas - more commonly from Yagi than log-periodic types. There is probably an element of luck in such cases and it is almost certain that they would get much better signals from one of the combined VHF/UHF antennas that are now on the market. Viewers who enjoy consistently satisfying UHF reception via an indoor antenna should count themselves even more fortunate, in that UHF signals are very vulnerable to absorption or deflection by metal beams, wiring, metal furniture, blinds and even people moving around the room. Luck aside, the logical starting point for good UHF TV reception is an adequate UHF antenna, designed for the relevant band(s) or channel(s), mounted as high as practicable on an outdoor fixture or mast and orientated as accurately as possible towards the distant transmitter(s). The present UHF band/channel frequencies. by the way, are as shown below. Band 4: Channels 28-35; 526582MHz. Band 5: Channels 39-69, 603-820MHz. If combined VHF/UHF reception is required, as in Sydney, the options are a new VHF/UHF array or a separate UHF antenna. Because of the high frequency and small wavelengths, UHF antennas use quite short elements and are much less unsightly, cumbersome or damage-prone than their VHF counterparts. At the same time, they are highly directional and this provides greater discrimination against "ghost" images. (It also requires the antenna to be pointed accurately towards the transmitter). Typical UHF antennas currently available are the 10-element (TC-10) and 18-element (TC-18) Yagi types from Hills Industries. Separate versions are available for Band 4 and Band 5 reception, with the gain, front-back ratio and directivity of the TC-18 being superior in each case. For further comment and details of an alternative homebuilt high-performance "bow-tie" Band 4/5 antenna, see SILICON CHIP for January 1988. Coaxial cable, diplexers, &c If . the antenna needs to be carefully installed, so must be the · signal feed to the TV set. An unduly long downlead is a no-no; 300-ohm ribbon is out; nondescript coaxial cable is out. unless you are sure that it is of 70-75 ohms impedance and equal to the task; so also are nondescript baluns, splitters and diplexers left over from the VHF era. By way of interest, a spec. sheet for once-popular general purpose coaxial cables indicates imped;mce figures from 45 to 75 ohms. Of the 70-ohm types rated for operation at 600MHz, the attenuation figures, converted to metric, range from 17dB/100m. to just over 40dB/100m. If correctly identified and in good condition electrically, the first should still be OK for UHF TV: the second, hopeless! The attenuation of modern general-pupose VHF/UHF cable ranges from about 19-25dB/100m at 600MHz. equivalent to 2-3dB for a domes tic down-lead of around 10m. For longer runs. or where losses are critical. the more expensive semi air-spaced cables can reduce attenuation by 2:1 or more. In typical installations, the need may arise for the occasional balun, combiner, splitter, diplexer or outlet and again, it is essential to ensure that the unit chosen is suitable for UHF signals. Possible receiver problems It would be nice to be able to say that, with the antenna system spic and span, the remainder would be automatic. Not quite! Some older receivers rely on manual tuning for UHF coverage. You click the normal VHF turret tuner around to a "U" or "UHF" position, then carefully rotate an ordinary tuning knob until the wanted signal appears - hopefully somewhere near the appropriate number on the dial scale. Turn too far one way and the picture dissolves into streaks; too far the other way and the colour disappears first , followed by the picture and finally by the sound. With a light touch and a little practice you should be able to get it right, making sure not to overlook the AFC (automatic frequency control]. Don't forget the old adage: when all else fails, read the instruction book! If only one UHF station is involved, it should normally be possible to leave the UHF tuning preset and simply switch to "U", as necessary. If there is more than one, you'll probably start saving up for a receiver with a pushbutton tuner - or you'll begin using your VCR as the tuner. (See our article entitled "UHF Shenanigans With a VCR" in the December 1987 issue). Whether in the VCR or TV set, pushbutton tuners avoid most of the hassles. In general, the setting-up procedure is exactly as for a VHF station, except that the little bandset slider has to be set to "U' ·. Again, don't forget the instruction book! Whether the tuner is manual. preset or automatic. the ultimate quality of the picture in terms of noise content is going to depend on the intrinsic signal/noise ratio of its front-end circuitry . The SIN ra tio may be much the same as for VHF. in which case your efforts with the UHF antenna could reward you with an even better picture . But don ·t be surprised if the UHF tuner Problems? ... and you don't have our 112 page catalogue ... you've got real problems! ARISTA ... your one-stop problem solver. Audio leads ... Batteries ... Chargers ... Battery holders ... Cables ... Car accessories ... CD accessories ... Converters ... "Cutec" ... Earphones .. . Fuses ... Headphones .. . Intercoms ... Knobs .. . Microphones and accessories ... Mixers .. . Multimeters ... Plugs/Sockets, etc ... Plug adaptors ... Power packs and leads ... PA ... Disc and Tape care ... Security equipment ... Signal modifiers ... Solderless terminals ... Storage boxes ... Switches ... 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(03) 543 2166 (3 lines) Errors and om1ss1ons e)(cepl ed PrrcPS ;m<f <:,pec1llcat1ons SUbjC!Cl !O ·t>ange :~:~~~!;., ~ '. ;r·~.;~_1;•~~:;:~7,~;;~:\ f.1.1 hlr,•· ·[).,p, •;;~, ' Aopit·,·,irf'<)''i'•>rf>ntr. ► h•m.ir ► rNJ•-,t,•r •· 1 'r.tdrn,1r~·- t lht·, rf'',j3P<. ' •vt' l N fh'r" ■ESZ THE WAY I SEE IT - CTD is down a bit, in which case, you will need all the signal you can get to preserve the status qua! Do as I say - not as I do! Now comes the moment for confession! Some years ago, in an effort to improve reception of SBS channel 0, I installed a Hills log periodic antenna designed to cover VHF TV channels 0-11, as well as the FM band. Since it provided ample signal from the TV stations, it seemed like a good idea to insert a home-made resistive splitter in the cable - within easy reach of the man-hole - to feed the FM tuner as well. Rather than cut the original cable, I hauled it back and left the surplus lying loosely in the ceiling space, running an extra odd length of coax from the splitter to the TV set and a few metres of 300-ohm ribbon to the FM tuner. Don't laugh, it worked fine , apart from occasional (and fully expected) interference to channel O from the nearby high voltage mains. Some time later, facing the need to convert to channel 28, I mounted a TC-10 UHF Yagi on the existing VHF antenna support, pointing in the general direction of channel 28. Signals from the two antennas were brought down by short lengths of coax to a VHF/UHF combiner. tucked up under the eaves, and thence on to the receivers via the original length of ea ble in the ceiling . VHF and FM reception appeared to be totally unaffected hy the change - good, clear, virtually noise-free pictures from all channels. As for channel 28, John Logie Baird would have been enraptured with it back in 1930 but by present standards, it was appalling: a wobbly, tinted image seen through an overlay of dancing dots! So I climbed into the ceiling and re-arranged the 300-ohm ribbon into a separate folded dipole to suit the FM band and suspended in the rafters, broadside on to the general direction of the incoming FM signals. The splitter was removed and the cables to the TV receiver connected end-to-end and taped over. The UHF signal was certainly much better now but by no means noise-free. So, on the next cool day, I climbed back up into the ceiling and by dint of much wriggling and grunting, removed the extra piece of odd cable and re-routed the original single length so that it ran directly across the ceiling, down the wall behind some curtains to the VCR and TV set - with a couple of metres to spare. This time around, the UHF signal had edged up into the virtually noise-free category - provided it was fed first to the VCR. acting either as a preamplifier or tuner. Clearly, its signal/noise ratio was better on UHF than that of the TV set. With hindsight, even though my location is average/good for UHF, I would probably have been wiser to spend the extra few dollars on a TC-18 Yagi and benefit by the extra 3dB of forward gain. Of course, I guess I could get really industrious and build Bob Flynn's four-bay bow-tie effort in the January issue! Or I could over-compensate by following the lead of one viewer I heard about, who lives below the If your TV set doesn't have a UHF tuner and you don't have a VCR, this UHF-to-VHF converter can be used instead. This unit is available from Tandy Electronics. escarpment separating SBS channel 28 from one of Sydney's beachside suburbs. He's installed a high-gain UHF antenna followed up by a masthead preamplifier. Despite that escarpment, his dilemma now is that his VHF reception looks crummy against channel 28 ! Ahead: facing up to reality As indicated earlier, the DTC is currently proceeding with the introduction of UHF TV. In some cases, as in Sydney, there is little immediate alternative to using it to supplement the existing VHF service which occupies "non-problem" channels. In other areas, involving the FM band or otherwise inconvenient channels, it may make more sense to opt for an all-UHF service, providing for extra channels and strategically placed, shared UHF transmitting antennas. In the short term it may be more traumatic but it should obviate the need for multiple receiving antennas. This latter course represents the hard core "reality", referred to earlier, with which the industry and viewers will have to cope. At the top of the list for full-scale VHF/UHF conversion is the 11lawarra area - the coastal strip south of Sydney, generously dotted with picturesque hills, mountains and escarpments. The Newcastle area, north of Sydney, will follow in 1990. If all goes to plan, VHF TV transmissions in the Illawarra region will cease on January 1, 1989 and apart from those who are able to snag signals from the Sydney VHF channels, south coast viewers will be entirely dependent on UHF TV. How reception will compare across the total community remain~ to be seen. I'd be surprised if there weren't plenty of complaints over the first few months. But will things go to plan? Will all the UHF transmitters be up and working in time, providing the planned coverage? Will the majority of viewers be ready for them? Will the VHF transmitters actually be switched off on January 1? Nobody's quite sure or, if they are, they aren't saying. But don't count on it. ~ MAY 1988 17