All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
alan: Sell it on and get a Freesat+ box. Sky want money to enable recording, even of free-to-air transmissions. This unwanted feature is built in to their firmware.
It appears that some Sky boxes could have different firmware loaded - see http://www.steves-homepag…3159 for an example. However, since that involves soldering cables onto the circuit board to use the external firmware-loading circuitry (JTAG), it's really only for the serious, dedicated enthusiast - and you still have to find someone who's bypassed it for your specific model of box.
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john mccrimmon: Very few boxes/TVs have audio description. Those that do may put the setting in different places.
General tips: Look for an 'AD' button or an ear symbol on the remote, or look in Preferences or Settings in the box or TV's menu system.
Receivers should all have some way of selecting which soundtrack to listen to, if more than one is being broadcast - the setting might be in the same menu.
This article talks about selecting it as a separate soundtrack, as if it were premixed, but it's usually carried as a limited extra audio stream that the box or TV has to mix with the regular soundtrack. That way, it uses far less space, but it means the receiver must specifically support AD.
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Tim Searle: There are five parameters for DVB-T transmission:
- Bandwidth
- Number of carriers/symbol time ('Mode')
- Modulation
- Forward Error Correction rate (FEC)
- Guard Interval
The bandwidth is the range of frequencies used for each multiplex. In the UK, and in the UHF band in Europe, this is 8 MHz to match the width of an analogue transmission.
The symbol time, which implies the number of carriers, is the guaranteed number of time ticks a pattern of signals (a 'symbol') is on air before it changes to the next pattern. Before switchover this was 2K, after it is 8K.
Modulation indicates how many different values a carrier can have. QPSK is four (two bits), 16QAM 16 (four bits), 64QAM 64 (six bits).
Forward Error Correction is a measure of the proportion of bits that are input and output compared to the number carried on air. Supported values are 1/2, 2/3, 3/4, 5/6 and 7/8.
The guard interval is some extra time, as a proportion of the symbol time, that the symbol is held for, to allow for echoes or multiple synchronized transmitters using the same frequency. The values are 1/4, 1/8, 1/16 and 1/32. All UK transmissions currently use 1/32. The further away an echo is expected to come from, the more time is needed to ensure it doesn't fall into the guaranteed symbol time.
At Emley Moor, all SD transmissions use an 8 MHz bandwidth, 8K mode, 64QAM modulation and a 1/32 guard interval. The PSBs use 2/3 FEC rate, while the COMs now use 3/4. It gives more capacity, but is less robust - it needs more signal, compared to noise and interference, than the PSB mode.
You shouldn't actually need to tell the box all this information, as it is all carried in many Transmission Parameter Signalling carriers that repeat many, many times per second. They use a very simple robust encoding which should be receivable even if nothing else is, and the same encoding is used whatever the other parameters (OK, for different numbers of carriers, and different bandwidths, they are found at different frequencies and held for a different length of time).
HD uses DVB-T2 which has a few more parameters, and a few more values for the parameters given, but the basics are still the same. Fully described, the HD transmissions are DVB-T2 8 MHz, 32K extended mode, 256QAM rotated, FEC 2/3, GI 1/128, Pilot Pattern 7. It requires roughly the same signal strength/quality as the SD PSB muxes.
Most boxes cope with a change in modulation depth, FEC and guard interval without needing a retune, but yours obviously doesn't. Since it appears with 100% quality in the Manual Retune screen with the values set to Auto, it can probably pick up the values from TPS when tuning, it just doesn't pick them up when you select a previously-stored service. It might take slightly longer to change channels if it had to wait to check TPS, I suppose.
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K. SMITH: The short answer is no. You will have to pay full price for a box and dish installation, if required.
There is a limited amount of time that eligible people can apply for help from the help scheme - up to six months before, and one month after, the last switchover date for your region. Manchester, part of the Granada region, completed switchover in December 2009 so the scheme ended there in January 2010.
The scheme offers to convert a single TV to digital using whatever is available - either Freeview, through an aerial, or a free satellite solution: Freesat or Freesat-from-Sky. It's available to people over 75 or otherwise less able to help themselves. Pensioners under 75 have to be either disabled or in a care home to qualify.
The standard option costs £40 but you can pay more for a satellite system if Freeview was the standard option for you, or for a PVR if you want that. The price list for alternative options is set by the installer who won the contract for the area.
Equipment is free if you qualify for some income-related benefits like pension credit or income support.
Sky will of course send a free box to anyone who takes out a subscription, but you'll be tied into a minimum £20 per month for a minimum of 12 months. Most Freesat boxes are cheaper than £240. You can get a regular SD box for as little as £35, and HD recorders from £170.
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des drumm: It won't be broadcast from Strabane, but you may be able to get either overspill coverage from Saorview transmitters in the Republic, or coverage from the mini multiplex that Dave Lindsay mentioned. The signals from Brougher Mountain may travel well enough for you to receive it.
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FJC: PSB = Public Service Broadcasting. 'Channel 3' (ITV1, STV, UTV) and Channel 5 still have public-service broadcasting requirements as part of their licences to operate. Channel 4 is a state corporation just like the BBC is. The PSB multiplexes are only permitted to carry channels from the public service broadcasters, or from the BBC. (The Rabbit services are the commercial services from the former public teletext licence holder Teletext Ltd. Since they gave up the teletext licence, they should have been booted off.)
COM = Commercial. These multiplexes can carry any channels they like/can lease space to; although Ofcom have to agree to changes in the line-up, they must permit the change unless "the capacity to appeal to a variety of tastes and interests would be unacceptably diminished."
The other names are simply the companies to whom the multiplexes are licensed. D3&4 is short for Digital 3 and 4 Limited, a 50/50 joint venture between ITV Network Limited (itself jointly owned by the 15 regional Channel 3 licence holders - ITV plc now owns 12 of these, STV plc two and UTV one) and Channel 4 Corporation.
SDN Ltd originally stood for S4C Digital Networks. S4C flogged it to ITV plc in 2005.
Arq is short for Arqiva, the transmitter mast owner/operator. It's a meaningless invented name, adopted after the company's previous name, NTL, was destroyed by the cable TV operations (which were demerged).
According to the licences, they are still named 1 (PSB1, BBC A), 2 (PSB2, D3&4), A (COM4, SDN), B (PSB3, BBC B), C (COM5, ArqA), D (COM6, ArqB). The company names are used here to differentiate before and after switchover channel line-ups and modes.
Mux A is a COM and Mux B a PSB because in the 1998 line-up, Mux A was required to carry S4C and Channel 5, with the other half leased to commercial channels, while B was wholly pay-TV along with C and D. When ITV Digital went into administration in 2002, it surrendered the mux B, C and D licences, which were re-auctioned. The BBC and (then) Crown Castle won the beauty contest. Crown Castle's UK transmission operations changed hands again, to National Grid Wireless, before ending up with Arqiva, so you'll see CCI A and CCI B, and NGW A and NGW B, in some older documentation. There wasn't enough space to keep four public-service broadcast multiplexes at all transmitters, so Mux A was changed to commercial status, with S4C and Channel 5 moving to Mux 2/D3&4.
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mike butcher: Yesterday is free-to-air on UK terrestrial TV, through an aerial, but on satellite is only available through a Sky subscription.
mike: UKTV doesn't currently have a catch-up service that I'm aware of.
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PaulN: The new Divis mast's main antennas are not suitable as the coverage required is directional: 2kW in one direction, 1kW in another. Divis' antennas are omnidirectional, equal power in all directins. There isn't sufficient space on the new mast for the additional antenna required. I assume that the full requirements for the NIMM weren't worked out before the plans for the new Divis mast were submitted, or it would be too tall for Belfast Airport's flight path if the NIMM antenna were on there as well.
There *is* space, or will be, on the Black Mountain mast. Black Mountain was deliberately sited very close to Divis by the Independent Television Authority in the 1950s, so that viewers' aerials would point in the same direction for both BBC and ITA (i.e. UTV) signals, and a combo aerial for VHF Band I and III would be possible. VHF signals were shut down in the mid 1980s, but from 1997 Channel 5 used this to their advantage, sending out 50 kW from the top of the mast, rather than having to settle for a poor location much further down the Divis mast.
The confusion arises because Black Mountain is also a low-power UHF relay for BBC One, BBC Two, UTV and Channel 4 analogue. The transmitting aerials for this are way down the mast, they are only intended to cover a small area which is otherwise shadowed from Divis itself.
For the standard PSB mode, 64QAM 2/3, about one-fifth of the power of analogue was believed to be required to give the same coverage. Some sources say one-tenth, and the experience seems to be that one-fifth gives a larger coverage area than analogue. For this reason, the commercial multiplex operators have decided to start using a higher-capacity mode, 64QAM 3/4, which requires 1.5x-2x the power of the PSB mode to give equivalent coverage. The mode selected for the NIMM requires less than one-tenth the power of the PSBs, or 1% that of analogue, to deliver equivalent coverage.
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RayM: It's usually when the last programme before Weatherview finishes on BBC One, but can be earlier if that programme goes on for a while. ITV1 and C4 seem less bothered about a clean shutdown than the BBC do.
The BBC One schedule shows 'Who Do You Think You Are? USA' ending at midnight, then 'Celebrity Apprentice USA' ends at 1:25am. So either of those.
ITV1 joins 'The Zone', from a repeat of The Cube, at 12:30am while C4's 'Desperate Housewives' ends at 12:10am, followed by PokerStars North American Poker Tour until 1:10am. Channel 5 has CSI Miami until 12:55am.
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Monday 13 February 2012 1:17PM
Line of sight is not required for UHF television reception. It's recommended, because the UHF signals don't refract all that much, but they *do* refract over terrain and in some places that will be sufficient.
If signals didn't refract over roofs of neighbouring houses, very few people would be able to receive from terrestrial transmitters!
This refraction *also* contributes substantial amounts of interference from distant transmitters. The BBC's R&D white paper on planning states that Crystal Palace is a significant interferer over a square with edges 750km long:
BBC RD - Publications - White Paper 048 UK Planning Model for Digital Terrestrial Television coverage
That white paper describes how the prediction software for the UK Planning Model works. Digital UK's trade view is basically the output of the latest version of that software. A more detailed look at the algorithms can be found at:
http://downloads.bbc.co.u….pdf
http://downloads.bbc.co.u….pdf
http://downloads.bbc.co.u….pdf
(These are by J. Causebrook, the author of the PhD thesis referenced by that white paper.)
The amounts of refraction and reflection change over time with changes in weather conditions. Digital UK's predictions also take account of the statistical variation of signal strength and interference, across a grid square and over time.