I'm sorry, but I must step in and inject a chord of reality into the speculations in this list about European, and specifically UK, DTT. We may be across an ocean from ATSC-land, but we're not on Mars, and the facts are on record: 1. Analog TV in the UK is neither exclusively nor even predominantly low power or local. The first level of coverage, the UHF main stations, have typically a pair of 40kW PSP transmitters per service, combining with three or four other services into a usually omnidirectional HRP antenna, giving 500kW or 1MW ERP per channel. The original (1960s) main stations are located close to major population centres (London, Birmingham, Cardiff, Manchester, Newcastle etc.) with an average spacing between stations of some 80 miles. They serve by far the majority of the country's population. The second layer fills the gaps: these transmitters are generally located in rural areas rather than close to any one major city (Heathfield, Hannington, Sudbury, Sandy Heath, Waltham, Bilsdale etc.) They are also in the 500kW class, at intervals of about 50 miles. Only after that do we get down to the relay stations, with power levels anywhere from a handful of watts up to 10kW. Unlike much of the USA, where cities are on the plains or in wide basins, the UK's history has placed settlements preferentially in valley locations, often shielded by steep hillsides from geographically distant main stations. Western and northern parts of England, and most of Wales and Scotland in particular, are difficult to serve from main stations, and are littered with low power transposer sites, each serving its own small pocket of population. Even some sizeable UK cities (Sheffield, Bristol) are notoriously hilly and are covered, according to local topography, by a combination of distant main stations and local relays. Here in Sheffield for instance, antennas can be seen pointing not only to the local high power station (Emley Moor, 20 miles) but also to those in adjacent regions (Belmont, 55 miles; Waltham, 45 miles), as well as to the local relays. So it is not at all unusual for fixed (rooftop) antennas to receive their TV over a path in excess of 40 miles, and in places as much as 70 miles. In the low-rise city suburbs set-top antenna use is widespread, though 'main set' installations in private houses generally use rooftop or loft-space yagis, not so much because of low field strengths as to overcome multipath or co-channel. Of course the UK differs from continental Europe in that apartment-dwelling (and with it the communal antenna system) is not so widespread here, outside the inner-city areas. 2. Digital TV uses the very same transmitting stations, but at an ERP (per mux) nominally 20dB (pending analog switch-off) below the analog peak sync value. So the signal paths and service areas are essentially the same. Multipath isn't such an issue, but CCI is, and digital coverage is often limited by the presence of co-channel analog signals from distant stations. Where field strengths are low, impulse interference can be the principal impairment to indoor-antenna reception. In addition, the comprehensive nature of the original 4-channel UHF analog service plan has meant that (again, pending ASO) in some areas one or more digital multiplexes has had to be allocated a frequency outside the locally-grouped antenna sub-band, so new wideband receiving antennas have been needed. 3. Most of the London area is well served by the 1MW analog, 6.5kW digital ERP from Crystal Palace in South London. The (Villiers Street?) ground floor location described is a mere 6.1 miles from CP, though shielded from the direct signal by the buildings across the Thames, and by the heavy girderwork of the Hungerford rail bridge. Not an untypically difficult UK city-centre location for indoor antenna use, and field strength should be quite adequate even for a receiver of modest performance. So we needn't be surprised if a retailer just up the road from there can demonstrate set-top DTT reception, and a second-floor apartment-dweller get by quite happily with a Silver Sensor. 4. But... those legacy 'professional' rooftop antenna installations out in suburbia are not all they may appear. Many date from the end of the 1960s when UHF PAL colour took over from VHF 405-line black and white. It's not at all unusual to see broken or missing elements, drooping booms and quarter-inch open-braid single-shielded co-ax. The DTG and the Confederation of Aerial Industries are working hard to educate installers and the public on the importance of a suitable antenna, correctly installed and with good quality feeder. The public is resistant, and often incredibly tolerant of the slow decline in their analog picture quality. But they're not so happy to accept glitches in their digital reception, especially when the upgrade coincides with the purchase of a large plasma screen. So it says a lot that the COFDM system is so robust that in the majority of cases it delivers customer satisfaction without an antenna upgrade. That this can happen is surely at the root of Freeview's success in the Sky-sceptic, technophobe majority of middle England. 5. The suggestion that first-generation COFDM receivers had better tuners is belied by even the most cursory test of the products themselves, and by studies carried out by Digital Television Group, the UK industry's independent and confidential testing organisation. The first COFDM STBs were built for the failed On-Digital (later ITV Digital) pay service; most used a basic analog TV tuner, with outboard IF filtering and amplification prior to the ADC. Intermodulation performance at both RF and IF was poor, AGC was not optimized for digital, and typical noise figures were in the region of 9 to 12 dB. Demods were 2-chip or first-generation single-chip jobs, and frankly a little rough. These units had poor echo tolerance and struggled, mostly failed, to meet the DTG's target sensitivity of -78dBm (QEF BER with a 2k 64QAM 2/3 1/32 signal in a Gaussian channel) and analog ACI protection ratio of -35dB. And they just threw their toys out the pram when presented with interfering analog signals above about -25dBm -- a bag of boosters and another of attenuators was part of every installer's kit. The first boxes sold for Freeview were modified (or in some cases unmodified) On-Digital products -- the card slot wasn't needed. But with the first generation of Freeview-specific STBs in 2002 came an engineering-led drive for improved performance, as typified by my own SetPal design, long championed here by Dermot. With purpose-designed tuners these achieved 3.5dB typical noise figures, and combined with the latest COFDM demods they pushed QEF sensitivity to -83dBm (64QAM, equal to -87dBm with 16QAM) and ACI PRs through the -40dB mark -- in some cases as high as -45dB. The conventional tuner-can manufacturers had to sharpen their act, and newer designs from the likes of Philips and Thomson were soon up there with the original SetPal, giving even the cheapest boxes (now <$50 retail) almost the same performance margins. Despite the cut-throat price competition rampant in UK consumer electronics, most current Freeview receivers are so good there is very little to choose among them in terms of RF performance -- their technology has evolved to be the perfect fit for the Freeview plug-and-play DTT model. 6. I'd also like to demolish the old recurring myths about COFDM's alleged power budget inferiority (2dB, was it?) relative to 8VSB, for equivalent payload and error protection, and the mystical belief that somehow the European system degrades faster than the US ouside a 'sweet spot' of range from the transmitter. The first is based upon DVB/ETSI specification implementation margin minima rather than the real sensitivities achieved by almost all demods since 2002, and in an unrealistic Gaussian scenario at that. Any real differences are so small they'd be absorbed in cable length or antenna gain variations, rather than demanding transmitter power increase. The second has nothing to do with modulation; it originates from one flawed field study and has been perpetuated within this list to the level of dogma, by those who surely know better. But I haven't the time to present my case right now. Season's Greetings to all! Stephen ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.