All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Vincenzo Mesce: It's definitely running on Freeview and on Virgin Cable. If you're using Freeview, and you have compatible equipment, it should be on 103 alongside BBC One HD on 101, BBC HD on 102, and 4hd on 104. You need a TV, set-top box or PVR with the Freeview HD logo; an 'HD Ready' or 'HD TV' logo is not enough. Check the manual to ensure that it lists support for DVB-T2, not just DVB-T.
It is expected to launch on Freesat and Sky early next year (UTV's press release says 'first quarter').
| link to this comment |
Nicholas Willmott: In some cases, because another transmitter will now be sharing those frequencies, or will be once a neighbouring group is changed. In others, because this group will be temporarily sharing until another group is changed (these may be temporary). Then there also seems to be a small group that is changing due to greater-than-anticipated interference from a station that isn't being changed. Some in west Wales may be down to greater-than-expected interference from Ireland - one of Ireland's transmitters had to change frequency due to greater-than-expected interference from Preseli.
In this batch, Trefin and Llwyn Onn get a power increase on C22/C25/C28, which aren't frequencies used in the clearance programme. They will be joined in two weeks by Waunfawr, Bethesda North and Morfa Nefyn. My guess is that probably the commercial muxes from Blaenplwyf are going further than they were supposed to, unless it signals an upcoming 3 dB increase of Blaenplwyf COMs, which are 6 dB down on the PSBs, rather than equal or only 3 dB down as at most other transmitters. The only other transmitters I'm aware of that have a larger-than-usual difference between PSB and COM power output are Brougher Mountain (10 dB down) and Belmont (complicated).
Similarly, the power increases on C41/C44/C47 at Ynys Pennal and Cwrtnewydd probably are to do with interference from Wenvoe, or maybe Arfon.
Briton Ferry has a *temporary* increase from 4W to 32W. It will change frequency (to C40), and return to 4W, when Wenvoe retunes, expected in March next year. (Wenvoe does not itself use C61 or C62, but has to release frequencies for Mendip, which does.).
| link to this comment |
sheila: The switchover help scheme has nearly ended. If she is in Northern Ireland you can still ask for help switching one TV to digital - see Region Northern Ireland | Switchover Help Scheme . This may be Freesat if Freeview is not possible, or they should offer Freesat as an option for a small fee.
| link to this comment |
John Durrell: The difference in what your TV reports is *probably* down to using an external receiver rather than having the HD tuner built in to the set.
This is complicated by the fact that, on Freeview HD, the encoding hardware, and therefore the transmissions, can dynamically switch between 1080i50 and 1080p25 modes for every Group of Pictures (GoP). A GoP is a sequence of 15-25 pictures that are encoded using differences between the pictures, only one whole picture being sent in the set. The encoder switches mode based on how well the content compresses in each mode - if the source material was actually captured in progressive mode, or if there isn't much motion, it should compress better in progressive mode than interlaced. If there is fast motion, it will look better in interlaced mode.
It is never anything to do with your aerial - the decision of whether to choose i or p mode for a group of pictures is taken by the encoding and multiplexing hardware in London (and the BBC's backup location somewhere in the Midlands). For BBC One Northern Ireland HD, and UTV HD, a lightly-compressed high-bitrate signal is sent to the code-and-mux centre for compression and multiplexing. The resulting multiplex is sent back to Divis, where Service Information for the other multiplexes is added. It is then transmitted from Divis and carried via line feeds to Limavady and Brougher Mountain, which also transmit it. The other, relay, transmitters receive off-air from one of those three and retransmit. (Similarly, BBC One NI and BBC Two NI in standard definition are sent to the BBC's code-and-mux centres, while UTV and UTV+1 in SD are sent to ITV/C4 facilities elsewhere in London.)
The reason code-and-mux is done in England is simply that the majority of channels on most of the multiplexes only have one version for the whole UK, mostly played out or originated in London, and it makes more sense to bring in the few differences rather than send out the greater amount of content that is the same. Also, the same content is uplinked to satellites for satellite reception, where all the content for a single transponder has to be combined into one multiplex and uplinked from a single location.
The raw, uncompressed data rate for 1080p25 is the same as for 1080i50. 1080p25 means that 1080 lines are refreshed in full 25 times per second, taking 1/25th of a second, while 1080i50 means that half of the 1080 lines are refreshed in 1/50th of a second, followed by the other half in the next 1/50th of a second. In both modes, any specific line is only refreshed 25 times per second. 1080p50 doubles that to 50 times per second. Much equipment drops the '50' from the end of the indication and just reports 1080i or 1080p.
When a GoP is encoded progressively, the receiver can still send it on to the TV in interlaced mode: it just sends the lines in a different order to how it received them. There is no loss in picture quality and no difference in the apparent motion of the picture.
It may be possible to set up your receiver to send 1080p50 to the TV, if both support it. To receive the 'HD Ready' or 'HD TV' logos, and even the 'Full HD Ready' or 'Full HD TV' logos, the TV only has to support 1080i50 input - it does not have to support 1080p50. They only have to support 1080p50 in order to receive the 'HD Ready 1080p' or 'HD TV 1080p' logos. (The word 'Full' indicates that the TV itself has 1080 display lines, without that word it might have only 720 lines.)
| link to this comment |
Sean Diamond: All YouView boxes meet the D-Book 7 requirements for HD and qualify for the Freeview+HD logo. It will therefore be able to pick up RT whether you get that from a UK or a Republic of Ireland transmitter.
| link to this comment |
Edwin Raymen: reception often does change over the course of the day, if it's marginal. (Either just above the signal-to-noise ratio required, or just below the point where too much intermodulation is occurring.) It's all to do with temperature and humidity, which affect how the signal travels, and also temperature of layers in the upper atmosphere, which in the right (wrong) conditions can bring in distant interfering stations.
Looking at Digital UK's prediction for the PE9 1DW postcode (which you put in the 'Your site' box) I see that there are three transmitters covering your area strongly, and two providing variable coverage. It may be that your equipment isn't tuning into the transmitter that the (presumably communal) aerial is pointing at. Many receivers just store the first services they find, when scanning from lowest to highest frequencies, which aren't necessarily the best quality versions. You could try retuning manually to see if you get better results from a different transmitter.
If you traditionally got ITV Central East/BBC East Midlands on analogue, your transmitter should be either Stamford or Waltham. If you got ITV Anglia/BBC Look East it should have been Sandy Heath, which is expected to give much better results than Tacolneston. There's a chance that you're now getting ITV Yorkshire East/BBC Yorks & Lincs from Belmont, which is predicted to be the worst option.
You could ask the aerial installer which transmitter the aerial is actually pointing at, and see if he can help you tune your equipment to the right frequencies. Alternatively, click the transmitter name links in the paragraph above to see the UHF channel numbers to try for each transmitter.
| link to this comment |
Edwin Raymen: Do note that even if you're tuned into the correct transmitter, it could still be down to *too much* signal rather than too little. The three best transmitters all show 99-100% coverage for the three PSB services, and Waltham shows 96-99% for the COM muxes, while Sandy Heath's figures are over 85%. (These percentages are the predicted likelihood of getting a reliable signal, rather than indicating a particular signal level - don't expect either signal strength or quality on your box to match these figures.)
| link to this comment |
vicki: Well, there haven't been any changes at the transmitter and Digital UK's prediction suggests that you need barely any gain from the aerial, so my guess is that either a cable has become disconnected somewhere, or that the aerial has been damaged or moved, or possibly that water is getting in somewhere.
All outside cables should be well anchored down to stop them moving, and rubbing against tiles or brickwork. If they do rub, the insulation wears through, which allows water to get in. Water changes the way the cables work, massively increasing the signal loss in the cable.
You are very close to the transmitters, so it could be a case of receiving too much signal, though I can't see why the received signal level would have changed. If you have any amplification (boosters), try removing it or turning it down. If that doesn't help, and nothing apepars to be broken, try adding an attenuator.
| link to this comment |
vicki: Additional thought - there was a retune event on the 31st, reorganizing the channel list. Did you retune? If so, it's possible that your equipment has stored a different transmitter from the best one available. Try doing a manual retune using Mendip's frequencies (if you had Freeview before switchover), which are: C61, C54, C48, C56 and C52 (and also C58 if you have HD).
You might find a better version of the services at a different place in the channel list, usually around 800 or so. If so, check which UHF channel/frequency those services are using, and retune manually using those frequencies.
Signal levels do vary over time, with changes in the weather conditions. It's possible that when you retuned, conditions were *just* good enough to detect the other transmitter and store the services. TV equipment should really check the quality and strength of each transmitter before deciding which version to store, and newer equipment (most Freeview HD boxes) does. Older equipment just stores the first version found when scanning from lowest to highest frequencies.
| link to this comment |
Monday 29 October 2012 2:25PM
conor, leslie rainer: As always it is up to the broadcasters to decide when to start HD services, and when to leave Sky.
The Astra 1N satellite has plenty of capacity: it has 52 transponders but only 20 of them are in use, and there are spare frequencies not currently in use. SES, the operators of Astra satellites, are in dispute with Eutelsat over who can use which frequencies, but that covers frequencies *already* in use, broadcasting from Eutelsat 28A, rather than unused ones.
Each channel's broadcaster will have to decide whether the anticipated increase in revenue from going Free To Air will outweigh the loss of subscription revenue from Sky, any bribe that was made (e.g. subsidising their transmission cost on a Sky-leased transponder) and the costs of moving to a transponder on Astra 1N. There are also differences in Sky's charges for FTA channels versus for pay channels.
Freesat as an organisation is unlikely to have the funding from its parents, the BBC and ITV plc, to be able to lease a spare transponder and encourage individual channels to move over, without getting a transponder's worth of channels to do it in one go. It will probably take a whole broadcasting organisation, e.g. UKTV, to decide to jump.