All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.NottsUK: It could be a new regional variation. LyngSat has it as ITV1 London, so it's possible that they're going to move it from its current home on 10832 H.
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John: Your loft aerial may turn out to be sufficient. If it's not bothering you, you may as well wait the few months to see how it turns out. If analogue pictures are clear, not fuzzy or ghosting, it'll probably be OK, at least for the public-service multiplexes.
If it's an older model, it may be a Group B type, which works for a specific range of frequencies (C35 to C53). The public-service multiplexes will be within this range, but the commercial multiplexes will be outside it. For loft aerials, it's recommended to stick to a grouped aerial as they give more gain for a given size. A semi-wideband Group E will cover both PSB and COM multiplexes.
You will nearly always get better results from an externally-mounted aerial, as the signal doesn't travel well through walls.
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NottsUK: ITV1 HD Meridian South-East is currently on Astra 2B, 11973 V - could be they want to make this free-to-air, joining London and Granada.
ITV sells advertising for different blocks of the country, ranging from parts of the franchise areas (micro-regions, based around one or two terrestrial transmitter areas) to whole franchise areas (regions) and combinations (macro-regions). Currently ITV1 HD appears to run on the macro-region level, with London and Granada (representing the North Macro - Granada, Yorkshire, Tyne Tees and Border) on Freesat and Sky, and Central West (representing the Midwest Macro - Central, Wales, West, Westcountry) and Meridian South-East (representing the South East Macro - Meridian and Anglia) on Sky only.
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ITV Media -
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The next logical step if they were launching a new variant would probably be to provide the West Macro (Wales, West, Westcountry - Midwest Macro without Central) with its own service based on ITV1 Wales, which is what they've done for ITV1+1.
Each ITV1 micro-region has its own stream on satellite, but only some of them are free-to-air - one representative of each news region is. The news region map now looks a bit different:
ITV Local | Local Regional News & Weather - ITV
(RG47SH)
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Gill: The aim is that everyone who got (or could get) good quality analogue signals before switchover should be able to get at least the public service channels after switchover. That means, in addition to the former analogue channels, the BBC's additional channels (CBBC, CBeebies, BBC Three, BBC Four, the BBC News channel and interactive streams) and many of ITV's and Channel 4's additional channels. In addition everyone should get Channel 5, which wasn't available to everyone.
The full range of Freeview channels will only be available from main transmitters, but should still cover about 90% of the UK population. The commercial multiplex operators refused the option to broadcast from the relay sites, which fill in gaps in coverage. See 'Freeview Light' for more information.
The analogue signals are switched off at the switchover date. It's Freeview or nothing, through an aerial.
To be able to give proper advice we need a full postcode to pinpoint where you are, and how good a signal you can expect to get. Most people won't need a new aerial, as long as the aerial and cables are in good condition.
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Olivier: The transmitting aerial at Dover has been replaced. It's very likely that the new aerial has been designed not to waste power broadcasting across the channel.
The planning application shows that 10 tiers of panels have been fitted to three sides of a spine with a regular pentagonal cross-section. The panels point to 36°, 324° and 252°.
While the replacement aerial is being wired up, analogue services are coming from the new reserve aerial. This is also 10 tiers of 3 panels, but the panels are attached to the north-west edge of the (triangular) mast. It's hard to read the angles off the diagram, but the panels pointing west and north-east seem to aim slightly further to the north-west than those of the main aerial.
The panels have a roughly cardioid radiation pattern, so some signal will go across the channel - but not nearly as much as before.
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If anyone wants to look at the documents, go to Error and click the External Documents tab, then click View Associated Documents. In the popup window, select 'Existing Elevations'. (RG47SH)
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Charles Stuart: DVB-T QPSK 2/3 provides 8.04 Mbit/sec with a 1/32 Guard Interval. 64QAM 2/3 provides 24.13 Mbit/sec. The broadcasters currently carry 7 or 8 streams in this capacity. You might get 2 or perhaps 3 SD streams in QPSK 2/3, though it does depend on how heavily you're prepared to compress them.
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Steve: Not all ITV regions are available on Freesat - some are only broadcast encrypted (free-to-view with Sky equipment and a Sky viewing card). The following micro-regions are only available to Sky subscribers:
Anglia West
Central East
Central South (Thames Valley North)
Central South West
Meridian North (Thames Valley South)
Meridian Sussex
Tyne Tees South
Yorkshire East
Some of these now only differ by the adverts shown. Central South and Meridian North (which briefly made up the non-franchise Thames Valley area) get the Meridian South news service and I believe Meridian Sussex gets Meridian South-East.
Yorkshire and Anglia appear to no longer runs separate west/east news services. The only loser as far as I can see is Central East.
For some reason Anglia has two free-to-air streams: East and South. They could probably scrap one of these to get Central East free-to-air - if they wanted to.
If you have Freesat, you will be given the nearest ITV micro-region that is broadcast free-to-air. I don't know the exact rules.
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brian: At switchover, the 'analogue' aerial BECOMES the full-power 'digital' aerial. There really aren't 'analogue' and 'digital' aerials, either for transmission or reception. There are only UHF aerials, designed for different frequency ranges. The transmitting aerials are grouped just as receiving aerials are (or used to be). The smaller the range of frequencies it supports, the more efficient, so Arqiva have had antennas custom-built for each site rather than taking the off-the-shelf designs.
The low-power digital aerials just can't handle the electrical power that will be needed after switchover. At most sites they don't cover the full area that the main aerials do, either, and they're usually way down the mast to restrict how far the signals travel. They're *designed* to hit the hills to stop signals going further than they ought to.
Aerial upgrades/replacements and transmitter replacements have to be done in advance of switchover. They're not going to shin up the mast between 12am and 6am the day of the switchover! The real switchover to the new equipment happens long in advance of the announced dates - and for some viewers, causes changes in reception because the new aerial's radiation pattern is different.
I'm not sure if the new transmitters actually support both digital and analogue transmission just by flicking a switch (or a virtual switch in some software), or whether an engineer has to replace the 'exciter' unit in the rack. Probably lower-power sites are dual-standard and high-power sites have a replaceable component - I know that both are available on the market, I don't know what Arqiva have purchased.
The equipment at most main sites is approaching or exceeding 40 years old. Dover was built around 1967 with ITV on UHF starting up in December 1969. Channel 4's equipment will be nearly 30 years old, starting on launch day in November 1982. It's all reached the end of its useful life. Some sites had aerial replacements in the 1990s - these sites usually aren't getting another replacement now.
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Friday 18 March 2011 4:01PM
Reading
Mark A: SD signals have 576 lines per frame, interlaced.
Public Service channels - the old analogue channels - are required to use 720 pixels per line, the same as usually used on DVDs. Commercial channels are allowed to reduce this to 706 or 544 pixels per line. Many of ITV's secondary channels use the lowest pixel counts even for widescreen pictures, which were really intended for use when broadcasting 4:3 pictures (544 pixels is roughly 3/4 of 720 - a 4:3 picture is 3/4 the width of a 16:9 widescreen).
These pixels are not square. A widescreen TV has a ratio of 16:9 or 1.78:1. 720x576 is a ratio of 1.25:1. The pixels are therefore 1.42 times wider than they are tall, or 0.7 times as tall as they are wide. This is the 'Kell factor'. A 544x576 pixel widescreen picture has a 0.525 Kell factor.
Freeview HD is using 1080 lines per frame. Most broadcasters are using square pixels, 1920 pixels per line, but the BBC are sticking with a 'Kell factor' of 0.7 and using 1440x1080 (interlaced), which substantially reduces the bitrate needed.