All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Briantist: In the map selector buttons, you have 'Soarview' rather than 'Saorview'.
For power levels, you're clearly using the figures from the spreadsheet, but ComReg have obviously just converted from dBW (as in the Geneva plan) to watts. Perhaps you could round the figures to a more meaningful value?
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Helmut, Dave: The Astra 1N satellite has a spot beam designed to just cover the British Isles with a reasonably-sized dish, and all BBC TV transmissions should be using that. The exact footprint may not be as well optimized as Astra 2D was, as 1N isn't designed to live here permanently, it will eventually join the rest of the Astra 1 family at 19.2°E after some of the new satellites - 2E, 2F and 2G - go up.
I think programme contributors recognize that it's not possible to completely prevent overspill into other countries, but as long as the BBC and its suppliers have tried hard to avoid it, it should be OK.
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CrisOC: The Midhurst mast has one set of antenna panels at the very top, then another cluster on one side just below the top. It's not entirely clear, but I believe the digital services come from that lower cluster rather than the main antenna at the top.
mb21 - The Transmission Gallery
At switchover, digital services move from whatever arrangements they've been using to the main antenna(s). (At some sites separate antennas are provided for the PSB and commercial services, although they're usually just stacked one on top of the other.)
Also, digital power levels are usually increased. The new level is based on the current *analogue* power level and is usually one-fifth for the PSBs and one-fifth or one-tenth for the COMs, which gives roughly equivalent coverage, usually a little more. If levels aren't increased it was because the digital signals were already at this level.
Finally, services usually move to different channels, which have less interference than they did before switchover. The PSBs usually take over old analogue frequencies at main transmitters; at relays it may be necessary to change them to avoid clashing with a main transmitter, or to change from a non-standard grouping to a standard one.
Because of clashes with other transmitters that are yet to switch over, ArqB will remain at 1 kW until 25 April, after London switches over. Because the mode also changes at switchover, the coverage will probably decrease compared to Mux D, although this is a channel change as well.
Ofcom's documentation also says there could be restrictions on BBC A, D3&4 and ArqA 'if required', to half the published power, until 27 June. However, this doesn't appear on the postcode checker, so they may have decided that it isn't required, unlike the restriction on ArqB.
For you, Digital UK's trade view shows no prediction (< 50% of your grid square expected to get reliable results even half the time) for Mux C and D at present. The prediction goes up to 99% or 100% of locations at switchover, which is probably due to decreased interference more than changes at Midhurst.
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HDMI connectors aren't an *absolute* requirement. HD Ready TVs were permitted to have a DVI connector rather than HDMI. They are also supposed to have analogue component inputs (five connectors: Y, Pb, Pr, left and right audio). You won't find any Freeview HD or Freesat HD equipment with either set of connectors, though.
If the TV does only have DVI, it must still support HDCP, the content-protection protocol, on that connector. Since, for video, HDMI is just a more compact DVI connector - it's electrically identical - you can get an adapter. You will also have to figure out how to connect up the audio, because unlike HDMI, DVI doesn't carry sound data. My TV appears to require a 3.5mm stereo jack connection while most set-top boxes or PVRs have a pair of phono jacks - these cables are readily available.
The thing you should *not* do is also connect the SCART cable. That just confuses things, mainly because the SCART connector has a SELECT signal. When the box is turned on, it puts a voltage on the SELECT pin; the TV switches to that connection automatically. HDMI also has a 'select' feature, so whether the TV selects the HDMI or SCART input will be down to how it prioritises the two functions. To eliminate this problem, so that it always uses HDMI, simply don't connect the SCART cable.
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Briantist: The additional 25 lines per field are not exactly unused, even in the original definition. They allow time for the raster beam to return to the top of the screen, and contain synchronizing pulses so that the TV can synchronize itself to the transmissions - so that the picture display starts at the right point and each subsequent picture displays at the same position, it doesn't 'roll' or slide.
One field on the 625-line system actually contains 287.5 lines. For the first field, the top line is only a half-line, starting half-way across the picture, and for the second field, the half-line is at the bottom, ending half-way across. The digital system extends these half-lines to a full line, making 576 lines.
Since the mid-70s, the field and frame blanking intervals have carried, primarily, teletext data, encoded so they don't disturb the legacy sync pulses. Some lines have been used to carry other signalling data like Programme Delivery Control.
The first half of line 23, the second half of which is the first visible half-line of the first field, can carry PALplus data, used to signal widescreen pictures. Channel 4 still use this system but it didn't catch on with the other broadcasters. Some digital TVs or digital transmissions that weren't set up properly might display these dots in the first half of the first line.
If you want the full, full detail, see http://pembers.freeserve.…tml.
The DVB specifications do offer ways to carry the data that would have been carried as legacy teletext or in the Vertical Blanking Interval, and for the set-top box to reconstruct them for an analogue TV. As I recall, they are used on satellite, but not on Freeview. One of the differences between the Irish Saorview system and Freeview is that Saorview boxes are supposed to support DVB-TEXT (EN 300 472) as well as MHEG-5 programs targeting the 'UK Profile' object model.
Anyway, this is getting seriously off-topic!
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ian from notts: This is general advice for boxes with a dish output connection, I'm not completely sure if the Humax boxes can be used like this.
The output from the Freesat box, marked LNB 1 OUT, *can* be used to feed a Freesat TV or another box, but it has limitations. If the Humax is on, not in standby, or is recording two programmes at once, the TV will only be able to tune into channels that use a compatible mode. The TV only has full control if the box is in standby, and is not recording using LNB 1 IN.
To cram more channels into the space available, while keeping the frequencies on the cable reasonably low, there are two selectable parameters: low or high frequency range, and horizontal or vertical polarization. The receiver has to tell the LNB which signals to put on this output, which it does by passing control signals back up the cable. When the box is on, it controls these signals itself, independently for LNB 1 and LNB 2. It only passes through the control signals from the TV if it's in standby and doesn't need to use that input.
Therefore if you connect the TV via LNB 1 OUT and the box is on, you can only watch channels on the TV that match the mode that the box has selected: taking an example, if the box was showing or recording BBC Three, you wouldn't be able to watch ITV2, because BBC Three is transmitted with horizontal polarization and ITV2 is vertical. You also wouldn't be able to listen to any BBC radio stations because they're in the high band and BBC Three is in the low band.
To get full control from the TV, you need a completely separate run of cable from the TV to a separate output on the LNB.
The Humax manual only shows using the LNB 1 OUT connection to feed into LNB 2 IN if you only have one connection to the dish available. This imposes the same limitations on what you can record on the second tuner, or watch through the box when recording a programme.
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Briantist: Ofcom don't have the 'Channel M' multiplex licence anywhere either, and that was issued more than two years ago!
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Roger: At that location you might have received one last year for Sudbury, and might not get one for Crystal Palace.
The booklet is downloadable at http://www.digitaluk.co.u….pdf .
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Paul P: Many boxes get confused if they have services stored from more than one transmitter. The solution seems to be to ensure that you only have services from one.
To do this, you completely clear out the channel lists ("first time installation" is recommended), then just tune in the transmitter you want - use manual search, and use the frequencies at the top of this page.
If you're in the north-east to south-east sector, e.g. in east Berkshire or north Hampshire, you may find that you can't yet get the commercial multiplexes from Hannington. In that case, you should tune back to Crystal Palace.
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Wednesday 22 February 2012 4:44PM
John Rourke: No, but Black Mountain will. Channel 5 analogue currently comes from Black Mountain, not Divis - the sites are about a mile apart.
If not, your equipment may still pick up transmissions from the Republic, depending on where you are.
At least, it will launch in October if RT have selected a preferred bidder in time - because RT are a state organization in Ireland, they must run a full competitive tendering process according to the EU's rules, they can't just hire Arqiva (the mast owner/operator) to do it. If someone else gets the contract, they then have to agree terms with Arqiva for access to the masts to get the aerials put up - though I think Arqiva have already started doing work speculatively.