All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.Collin: Digital UK's predictor predicts a low percentage probability of getting reliable results on the ITV1 multiplex at present (32%). The prediction is based on a single TV connected to a reasonably high-gain roof aerial using a relatively short run of satellite-grade cable.
On the 20th, all other multiplexes go high power when the analogue signals are turned off. The prediction goes up to 100% for all multiplexes.
An amplifier is likely to be necessary to offset the insertion loss of splitting the signal to 7 points - usually around 12 dB. The amplifier should have about the same gain as the loss in the splitter, to keep the level at each aerial point about the same as the system was originally set up for. We mostly deal with 'set-back' amplifiers or boosters added for who-knows-what reason, which aren't doing anything much useful, just adding noise. (Your set-top box or TV already has an automatic gain control: adding external gain just means the TV turns down the AGC to compensate. The amp only does anything if the TV's front end is particularly noisy, or if the signal is too quiet for the AGC to handle - but in this case there's probably too much interference to be usable.)
Bill Wright has some suggestions on amplifier problems at
http://www.wrightsaerials….pdf (RG47SH)
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Andrew Beckwith: the prediction for your postcode for the HD mux is equal to that of A, B and C. There's no prediction shown for Mux D as it clashes with ArqB from Winter Hill, since November 2009. Winter Hill is nearly directly behind the aerial, but aerials have a limited ability to reject signals from behind and the low-power digital signals from Sutton Coldfield are pretty quiet. (ArqB from Winter Hill is actually at reduced power until after Sutton Coldfield switches over, to reduce problems, but it can't be completely avoided.)
The HD transmitter is indeed Lichfield at the moment, but HD services will come from Sutton Coldfield after switchover. HD services are even quieter, only 4 kW, and the receiver needs more than twice as much signal as Mux 1 to pick up the HD services. There are a few other users of this channel in the area.
There won't be anything on C29. This site shows the frequencies that NGW suggested for possible 'interleaved' local services several years ago. It's a potential frequency allocation for the future. I have suggested to Brian that he does not show them at this stage.
C29 is the *second* such potential allocation - C51 is preferred.
A wideband aerial already covers C21 to C68. If anything launches, you may be able to receive it, although it depends on the power level and radiation pattern. The plan used to choose the interleaved frequencies allowed for a maximum of five channels below the analogue aerial group, and two above - this is because the aerials usually have a bit of gain outside the official limits. See for example Gain (curves), Again . Most Group B aerials will probably still give enough gain to be usable at C29.
A Group B or Group K aerial will normally have more gain for the same size aerial, or alternatively you can have a smaller aerial for the same gain. (RG47SH)
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Timbo: You might be able to get HD from Crystal Palace, but you won't get it from Guildford until next April.
I looked at Digital UK's trade postcode checker using the postcode GU1 2NZ. Reception of Crystal Palace looks pretty good now, but HD signals will suffer badly from August when Sandy Heath SDN multiplex moves to C31.
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You can get an idea of when your relay will complete switching at Digital UK - Relay transmitter switching times . It should have progress reports on the 13th itself. Currently it says:
Sandy Heath, Luton: 6am
Dallington Park: Mid-morning
Kimpton: Mid-afternoon
The document sent out to installers who have subscribed to the ALmanac says 6am for all relays, though. Anglia Aerial Installer Newsletter.
Fringe reception of all multiplexes from Sandy Heath won't happen tomorrow: the commercial multiplexes stay on low power and parking channels until September (ArqB), November (ArqA) and April 2012 (SDN). Nottingham commercial multiplexes stay on low power and parking channels until September/October.
Not sure where you got your statistic from. While Sandy Heath did transmit 405-line TV, it didn't go on-air until 13 July 1965 (16,710 days tomorrow). Anglia started in 1959, but it was from Mendlesham. Sandy Heath was really a new build for UHF. Source: mb21 - ether.net - ITV 405 line TV Transmitters - East of England and mb21 - ether.net - BBC VHF 405-line Transmitters where the original scanned document referred to a 'Huntingdonshire' transmitter. (RG47SH)
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Tacolneston Mux A is not showing for me: uses C53 with a + offset. Internet Explorer 8.
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Des Collier: In general the frequencies have been assigned with the best one going to BBC A, then D3&4, BBC B, SDN, ArqA and ArqB in that order. I'm guessing C60 has slightly less interference from other transmitters between step 2 and power-up day, which is why it was going to be used for ArqA until then, but C53 is better after the programme completes.
However, Sky Sports 1 and 2 have ended up on ArqB after switchover, and Arqiva's arm is being twisted by BT who went to a lot of trouble to force Sky to make the channels available. Arqiva have probably asked to use it for B rather than A.
As for why they stay on low power, as Brian says, other transmitters are still using these frequencies for analogue or for low-power digital services, and increasing the power here causes problems over there. Looking at the map, Tacolneston uses C53 for Mux A and C60 for Mux 2. The power-up at Belmont is scheduled for the same day as DSO 2 at Tacolneston.
(Actually, Tacolneston Mux 2 is moving to C59 on 17 August, which is Belmont DSO 2 - possibly to reduce interference on ArqB at Belmont?)
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Colin: ArqB is using a different mode than Mux B used to, which requires 3-4 dB more signal. If Mux B was marginal it's not surprising that ArqB is now not working.
The mode change is to increase capacity - that capacity is being used by Sky Sports 1 & 2, which the BBC was temporarily carrying on Mux B before today. All the channels had to come off Mux B as it's replaced by the HD mux. At some transmitters that switched last year, Mux D did not switch mode (to become ArqB) and that caused a lot of pain and confusion for existing and would-be Sky Sports subscribers, who were told they couldn't get the channels. BT Vision, TUTV, Sky Sports 1+2 and the Mendip transmitter | ukfree.tv - independent free digital TV advice
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Marie W: There are a few cable providers in the UK. However, you're probably on the free service, of just the analogue channels only, that they were required to provide to anyone who stopped subscribing.
Check whether you're in one of the areas covered by Virgin at Local TV - Virgin Media coverage | ukfree.tv - independent free digital TV advice . If so, try
Contact Us
.
Otherwise, if you're on the Isle of Wight it might be WightCable - see Contact Us . Around Irvine and Kilmarnock in the west of Scotland, or in Lancashire, it could be SmallWorld - try
Contact Us - Smallworld Cable TV, Fibre Optic Broadband and Phone
.
Most likely you're in a region where terrestrial analogue signals have just been switched off - perhaps Nottingham. They're probably now having to feed the analogue cable service using the outputs of some Freeview boxes - Freeview does not carry Teletext at all, subtitles are transmitted in a different way.
There's a thread at Analogue Cable Switch Off Starts - Cable Forum covering switch-off of analogue cable services - Virgin Media are migrating to all-digital cable service.
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Paul: Most likely you are using the Waltham transmitter. Waltham switches over in August.
You are predicted to get best results from Sutton Coldfield but Waltham should still be acceptable. The results from Nottingham are expected to be poor.
If you're desperate for HD you could try Sutton Coldfield/Lichfield. The aerial would need to point south-west, rather than east. Your existing wideband aerial should be sufficient. You will get West Midlands news rather than East Midlands.
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Monday 11 April 2011 4:17PM
Reading
Alan: HD services start at switchover step 2, on the 20th of April.