All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Phil, Briantist: The BBC radio transmitters website BBC - Help receiving TV and radio - Transmitters says 250W. The Ofcom sheet indicates 125W vertical polarization, 125W horizontal polarization. This appears to be consistent: the BBC site adds up the horizontal and vertical polarization.
Likewise Yorkshire Coast Radio is 125W HP, 500W VP.
Typical portable receivers will get some contribution from both polarizations. Traditionally, rooftop FM aerials were HP, because that's what the BBC initially used, but in-car works much better with VP so they eventually switched to mixed polarization.
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NigelD: Depends if Brian ever gets the real radiation patterns out of the broadcasters, gets better terrain data, and updates his prediction system accordingly.
Digital UK's predictor, which does have that information, does not show Salisbury as a possibility.
Looking at photos of the Salisbury tower, it doesn't look like any new transmitting aerials were added for low-power digital, suggesting that the radiation pattern is still that of the analogue cylinder fitted in 1968: BBC RD - Publications - R&D Report 1968-22 : Salisbury UHF relay station: Summary of installation . This transmitted very little power in your direction, about 1/10th of maximum, though the current antenna shroud looks very clean for a 40-year-old installation. Pictures at mb21 - The Transmission Gallery .
There was also a fairly pronounced vertical beam tilt of 1.5°, to limit range to a few kilometres.
The Poole and Cheselbourne relays use the same frequencies as Salisbury analogue, before and after switchover, so Salisbury had better not transmit much signal in your direction!
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andyboy: If you have two aerials close together, then they can interact with each other, the elements on one aerial reflecting signal onto the other or preventing it from reach the other. If you're going to fit two aerials they should be spaced a reasonable distance apart, say a bit further than the longest element on the larger aerial (this should be the reflector elements on the London aerial, for you).
If they're already a good distance apart, I'd look at whatever equipment you're using to combine the two aerials into one cable. You should really use a diplexer, basically a matched pair of filters that combines the lower frequencies from the London aerial and the higher ones from the Sudbury aerial.
Given your results, the diplexer's split point might be a bit too close to C41, reducing the level on that multiplex, or the roll-off might be too shallow. Consider swapping it for one with a split at C36 or C38: Online TV Splitters, Amps & Diplexers sales . This will harm analogue Channel 5 from Croydon, on C37, but that won't be around from much longer, and you'll get it from Sudbury if D3&4 is sorted out.
There's a chance that C31 to C38 might be used in future for new digital TV multiplexes, in which case you might find the diplexer knocks out a channel you need. You could try combining the aerial signals with a plain splitter, though you might find that you get ghosting on the analogue channels from Crystal Palace, from the small amount of signal picked up by the Sudbury aerial. Digital is much more tolerant of delayed signals.
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NottsUK: Found them eventually at Footprint Graphics 28.2 E - SES ASTRA ! The fact sheet has now also appeared at ASTRA 1N - SES ASTRA which indicates that it will cover the current frequency ranges of satellites in the cluster, but also fill in the gap at 10.95 - 11.20 GHz between 2D and Eurobird 1 (16 transponders).
No indication yet exactly which transponders/frequencies will be on which footprint though.
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Mary: Yes, Freesat+ recorders can record a whole series. See freesat+ | Record, Pause & Rewind Live TV & On Demand - freesat .
Compare the channels available on Freesat and on Freesat-from-Sky at Compare Freesat and Freesat-from-Sky TV | ukfree.tv - independent free digital TV advice .
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A couple of weeks ago, SES announced that ITV had contracted to lease three more transponders on top of their existing six: SES - News
Wait and see how much of 1N's capacity gets burned up with additional regional variants of ITV1 +1 and ITV1 HD. Perhaps ITV1 Central East can finally go free-to-air?
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MickO: There is no final national retune day. You will have to retune from time to time as services come and go from the multiplexes, but those dates are all that are planned in terms of multiplexes moving to different frequencies.
ArqB will move to final channel and final power level on 14 September.
ArqA moves to final channel and final power on 23 November.
SDN moves to its final channel and final power level on 9 May 2012.
The vertical beam tilt on the main antenna carrying the PSB multiplexes will be adjusted, to remove the restriction to the south-west, on 27 June 2012. For people further away from the transmitter, in the south-west of the coverage area, this will increase signal levels, although technically the transmitter power isn't increased and nor is the transmitting aerial's gain.
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Damian: What you get depends on where the aerial is pointing. If it is indeed pointing to Exeter St Thomas, or any other relay, you will only get the 'Freeview Light' service - the Public Service Broadcasting multiplexes. This is because the operators of the other multiplexes refused to extend their broadcasts to any other sites, saying it would cost too much.
If you provide a full postcode, we can see whether a full service is expected to be available from another transmitter, and what you'd have to do to get it.
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Josh: The transponders simply relay the signal from ground level, however it is modulated. Nothing needs to be done on the satellite to switch from PAL to DVB-S to DVB-S2. Only the feed from the ground needs to be changed - as the BBC demonstrated when they switched their feed on Astra 2D transponder 50 (10847V) from DVB-S to DVB-S2 a couple of months ago. DVB-S2 wasn't even started when Astra 2D went up in December 2000.
For compatibility, I would think any new or moved SD services will remain on DVB-S, while new or relocated HD services will go to DVB-S2 if a whole transponder can be cleared of SD channels.
Sky's last quarter report says that 3.8m of their 10.3m customers take HD. Remember that this costs an extra £123 per year (£10.25 per month) on top of the basic subscription and any additional channel packages.
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Monday 8 August 2011 12:24PM
Michael: Channel 5 have *contracted* Sky to use soft encryption. The space they are renting on the Astra satellite cluster is on the Astra 2A satellite's south beam, which covers all of western Europe. If they were not encrypting, so that only UK homes could decode the signal, they would have to pay a lot more for the import programmes that make up a lot of their schedule.
To go free-to-air they would have to pay more for their programmes - which I presume Channel 4 did when going free-to-air HD on Eurobird 1, also on a Europe-wide footprint, though they use an unusual mode - or move to a satellite with a smaller footprint. The only one in the cluster at 28.2°E with a British Isles footprint is Astra 2D, and it's full.
Ireland's RT has the same problem, only smaller - their channels, which should really be free-to-air, are encrypted on the 2D satellite so they don't have to pay for the rights to cover the larger UK market. The free-to-air solution for them is Eutelsat's KA-SAT satellite, which has spot beams covering much smaller areas. The drawback is that it's orbiting over 9°E, meaning a switch from free to subscription TV, or vice versa, is a lot more complicated than just replacing the box.
SES Astra recently launched a new satellite, Astra 1N, which is going to temporarily provide more capacity at 28.2°E before the new 2E, 2F and 2G satellites are launched. They were ordered in November 2009 and it can take a few years before they're ready to go up and into service. They're likely to replace 2A and 2B which were designed for a 15-year lifespan. 2A was launched in 1998 - making its end-of-life around 2013. 2B was launched in 2000 and is expected to need replacement around 2014. Hopefully the new satellites will have tighter beams, reducing rights issues.
2F is supposed to go into service late next year, then 2E in mid-2013 and 2G follows in early 2014.
It would be nice if Sky's two encrypted multiplexes could be kicked off 2D and more space made for free-to-air channels, and possibly also RT's transponder freed up. However, the UK regulator has no power to do this - Astra is licensed in Luxembourg.