All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.F Farrar: Digital UK's predictor (trade view) indicates that your best bet for HD services will be Hannington, but performance of the commercial multiplexes is likely to be intermittent. Alternatively, Midhurst should give good performance for the BBC and ITV/C4 PSB multiplexes, plus the SDN mux, but intermittent HD service.
The south-east does seem to have fewer relay transmitters to fill in the gaps in coverage. I think this may be because the Rediffusion cable network was quite extensive. Unfortunately the relay transmitter construction programme had pretty much ended by the time Robert Maxwell bought up, and killed off, Rediffusion in 1986.
If you find you can't get reliable coverage from any transmitter, you will have to consider satellite or cable. Freesat offers free-to-air channels, unencrypted, not requiring a viewing card, although the mix of channels is a bit different to Freeview.
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Josh: the problem is down to the law surrounding digital terrestrial broadcasting. Mux 2 (also known as PSB2, D3+4 after switchover) is required to be licensed to a consortium of Channel 3 companies and Channel 4 Television Corporation, and it may only be used by them to host channels run by Channel 3 companies (ITV plc, STV, Ulster TV, Channel TV) or Channel 4. They are required to host Five (main channel only) and, in Wales, S4C.
ITV plc runs multiplex A/COM4/SDN (bought from S4C in 2005). Arqiva run multiplexes C and D. For competition reasons - since ITV is a broadcaster and Arqiva owns the masts - they are not supposed to discriminate against channel operators, operating free auctions when a slot becomes available. They're certainly not supposed to force out existing channels. The regulator plays no part in deciding what channels are available on the commercial multiplexes.
Freeview Limited is just a marketing company, co-owned by the BBC, ITV plc, Channel 4 Corporation, BSkyB and Arqiva.
ITV plc *could* move ITV4 to D3+4 in place of ITV1+1. Channel 4 could move Film4 or 4Music in place of C4+1. This would free space on Mux D (COM6/ArqB) for more channels, but they would then be auctioned to the highest bidder.
Looking at the BARB statistics, ITV1+1 had already managed a 0.4% share for the launch week, ending 16 January. In comparison, on satellite and cable, the CBS channels you mention only achieved 0.1% each, so you'd think they'd struggle to pay as much for the slot as ITV do - ITV4 got 1.0%. C4+1 achieved 0.9%, Film4 got 1.0% and 4Music 0.3%, so C4+1 is worth nearly as much as Film4 and a lot more than 4Music, and costs fractions of the amount to run.
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David: if you're having trouble with Freesat you will have exactly the same trouble with the FTA channels with Sky. The easiest thing to do is to ask a neighbour who has a working Sky or Freesat box to check whether they get the channels you're missing. If they can, see if they will let you temporarily connect their box in your flat. That will indicate whether it's your box or the wiring.
Having problems with the lowest frequency is unusual. Usually the highest frequencies are the problem, as signals travel less well the higher the frequency is. It might indicate that the satellite and terrestrial signals are carried on the same cable from the head-end and split at your wall socket, and the filter to separate them again is cutting off at too high a frequency.
The intermittent interference is probably your mobile phone. Keep it well away from your TV, radio, set-top box, and any wiring. This could still be the cause of your problem: mobile phone signals are very close to the upper end of terrestrial TV frequencies and the lower end of satellite intermediate frequencies.
The LNB shifts down the satellite signals from the broadcast frequency (10714 MHz to 10936 MHz, for Astra 2D) to 964 - 1186 MHz. This is the centre frequency, bandwidth is 27 MHz so the C4 transponder covers about 10700 to 10727 MHz when broadcast, and 950 to 977 MHz on the dish-to-box cable. Terrestrial signals are anywhere from 470 to 854 MHz. The normal GSM frequency ranges for the '900 MHz' band are from 880 to 914.8 MHz, phone to tower, and 925.2 to 959.8 MHz, tower to phone. It's possible that there's a mobile phone tower nearby that uses the upper end of the frequency range, and that the cabling is somehow picking this up.
If you got good analogue terrestrial reception before, Freeview should be strong enough after switchover. However, the master aerial distribution equipment may well need to be replaced or retuned depending on exactly where you are, and therefore whther the local transmitter is using different frequencies after switchover, and how much signal distortion it introduces.
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M
Crystal Palace (Greater London, England) Full Freeview transmitSaturday 29 January 2011 6:26PM
Reading
Geoff: you have to have DVB-T2 equipment. 'HD Ready' TVs with integrated digital receivers that are more than a year old can only actually handle SD transmissions using the older DVB-T standard, and HD signals from external sources. The TV has to have the Freeview HD logo.
I'm assuming you've entered a postcode for someone else's address, or a second home. For the postcode linked in your post, the HD multiplex is on C58 from the Mendip transmitter, or on C46 from Crewkerne, C29 from Stockland Hill, or C47 from Wenvoe.
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Paddy: wideband aerials have significantly poorer frequency response at lower frequencies than an equivalently-sized Group A aerial. It's very unlikely that any new transmissions from Crystal Palace will be outside Group A.
For a comparison, see Gain (curves), Again .
The wideband response is a lot better at higher frequencies, but it's still better to use a grouped aerial if you can.
If I were you I'd keep using your old aerial. (RG47SH)
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D.Jukes: absolutely true. The aerial is designed to pick up a certain range of frequencies, and the frequencies carrying digital multiplexes have been slotted in, at most sites, between the existing analogue frequencies.
At sites that have switched over to digital-only transmissions, they have often taken over the old analogue frequencies.
The aerial is completely dumb - it simply causes the signal broadcast over the air to appear as electrical signals on the cable. All the tuning and decoding is done by the TV.
In a few cases, the digital signals could not all be fitted into the same frequency range as the analogue ones, and you might need a 'wideband' aerial that covers more than one of the groups. Or, at some relay sites, all signals may have moved to a different group. A wideband aerial can never be as good as a grouped aerial of the same size, however. Check the information for your local transmitter.
If you got a good analogue signal before switchover, and all the transmissions from your local transmitter are within the group that was used for analogue, you should not need a new aerial.
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Briantist: There's no reason to think that Astra 2D does not 'support' DVB-S2. It was launched three months after Astra 2B, which does currently host some S2 multiplexes. So, in fact, do some of the Astra 1 cluster e.g. 1H which went up in 1999. The S2 spec was first released in 2005.
From this, and the fact that some Astra 1 transponders were converted from PAL to DVB-S, I conclude that the transponders are just dumb amplifiers and relays of the uplinked signal.
The difference is that 2D's transponders are configured for the Fixed Satellite Service band, not Broadcast Satellite Service as 2B is. These are ITU terms - FSS covers 10.7 - 10.95 and 11.2 - 11.45 GHz in 27 MHz channels, and BSS covers 11.7 - 12.5 GHz in 33 MHz channels. The simple fact of the wider bandwidth gives higher bitrates, so can lead to false comparisons. The DVB-S2 spec does indicate that 30% or so improvement can be had from the same carrier-to-noise ratio, compared to DVB-S.
Right now the FTA broadcasters don't need DVB-S2, but they might do soon if any more leave Sky and go FTA. ITV has some FTV rather than FTA regions, but they're advertising regions (showing different adverts) rather than content regions (where the actual programmes could be different, though it's often limited to local news output anyway).
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M
Marlborough (Wiltshire, England) Freeview Light transmitterWednesday 2 February 2011 5:12PM
Reading
Colin: Marlborough does not transmit the so-called commercial multiplexes at all. You're getting fringe reception from one of the full-service transmitters. This is either going to be Salisbury, which is vertically polarized, or Mendip - horizontally-polarized but more powerful.
For the "Marlborough" aerial the problem is likely to be that it's just not pointing directly at the transmitter that you're picking up, and it may be the wrong polarization and/or the wrong group (Salisbury and Mendip are both Group C/D transmitters). Salisbury is also pretty low power, though substantially higher than Marlborough. Mendip commercial multiplexes are on relatively low power (10kW) until early 2012, and you only receive a small fraction of the signal if the aerial is in the other polarization.
Hannington multiplex C and D are on 10kW at the moment. This will increase to 20kW, to match the other four multiplexes, at the end of June after some other sites, in the Central TV region, switch over. Pre-switchover Mux A requires roughly twice the power, all else being equal, to provide the same coverage area as the other multiplexes. This is because it uses a different mode, which gives a higher bitrate (more capacity) but requires more signal/less interference.
Or, you could be talking about the PSB channels with commercials, on C28. This should be about the same reported quality as on C25, but levels of interference can differ between different channels due to the frequency allocations at other sites (e.g. the site interfering on C28 might not broadcast on C25). You'll have to provide a postcode for me to find out more.
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Brian: I notice you haven't picked up Ofcom's change in their version 2.0 document for Meridian. Due to the release of channels 61 and 62, channels 39 and 40 are no longer going to be released. They have therefore moved BBC B to C39 (which is a current analogue channel) from C51 (which isn't).
Ofcom revised every existing document on 5 January 2011:
Ofcom | Digital Switchover Transmitter Details
You can still find some of the old documents at Digital UK's almanac page:
Transmitter Network - Digital UK Almanac (RG47SH)
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Thursday 27 January 2011 2:44PM
Reading
Gareth Smart: I suspect your percentages are from the 'signal quality' meter rather than 'signal strength'. This meter is typically useless, as it usually shows the number of uncorrected errors, and you can see those - if the picture is perfect it will show 100%, any less than 100% and you're getting some picture or sound breakup.
I think it's most likely that your problem is too much signal. The first thing you should do is remove any amplifiers. If you don't have any, or that doesn't solve it, consider adding an attenuator.