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The engineers who designed the services created digital broadcasting systems that would allow the reliable distribution of bits using the same infrastructure of cables and masts (or satellites) that already carried the analogue services to millions of homes.
Part of the design process allowed for more than one television channel to be carried by the digital system using a long-established data-processing technique called "multiplexing", a word that had, by another route, also come to mean a cinema complex where several films are shown at once on different screens.
It was back in 1996 that Parliament decided that the UK should have a six-multiplex service.
The Broadcasting Act 1996 provided that these "multiplex licences" should be issued for 12 years with a one-time right-to-renew.
Independent Television Commission: 1, 2, A, B, C and D
The current coverage figures range from around 90 per cent of the UK population for the largest of the multiplexes down to around 70 per cent for the smallest.
Of these six multiplexes, two are wholly reserved for existing broadcasters who are guaranteed places on the multiplexes under the Broadcasting Act 1996. The first will be used by the BBC to transmit existing programmes in digital form and develop new digital services. The second is reserved for Channel 3, Channel 4 and Teletext Ltd whose existing services will be reproduced in digital form, and who can use the additional capacity available for new services. This multiplex will be licensed and regulated by the ITC.
Licences to operate the remaining four were advertised and three have now been awarded to British Digital Broadcasting plc (BDB). The fourth multiplex, the third largest in terms of UK coverage, has been awarded to S4C Digital Networks Ltd (SDN). It will carry the new Channel 5, S4C in Wales, and a certain amount of Gaelic programming during peak hours in Scotland.
The ITC named the "wholly reserved" multiplexes 1 and 2, and the others, by the level of coverage: A, B, C and D.
British Digital Broadcasting plc eventually launched their service as ONdigital on 15th November 1998, re-launched as ITV Digital on 11th July 2001 and went out of business on 1st May 2002.
ITV Digital handed back B, C and D multiplex licences to the regulator, who awarded them to the promise of a free-to-air service the BBC and Crown Castle International, a company formed by the privatization of the BBC's transmitternetwork.
When Freeview started on 30th October 2002, the BBC realised that the existing broadcasting "mode" used for the digital services was causing problems for some viewers. For this reason, some multiplexes changed from "mode 1" to "mode 2" (see the diagram at the end of the article), which provided a more stable signal, but with the loss of some channel capacity. See Freeview modes - a simplified explanation for a longer discussion about this.
This was not a problem for the BBC with six full-time television channels to fit onto two whole multiplexes. So, multiplexes 1, B, C and D changed to the robust mode, but 2 and A did not.
Ofcom plans PSBs and COMs
During the planning for the digital switchover, where the existing analogue channels are turned off over several years, Ofcom, now the regulator used the names PSB1, PSB2, COM4, PSB3, COM5 and COM6 to refer to the six multiplexes.
PSB refers to the "public service broadcasters" (BBC, Channel 3 licence holders - ITV plc, STV and UTV, Channel 4 Corporation, S4C - Sianel Pedwar Cymru, Channel 5 and the "public teletext service".
The PSB multiplexes have almost total coverage of UK homes - 98.5%, and are broadcast from all television masts in the UK, including 1,036 smaller ones that only carry the PSB services.
COM is an abbreviation of "commercial", referring to the two multiplexes held by Arqiva, the company that owns and operates all of the UK television transmitters, and SDN, a company owned by ITV plc.
The COM multiplexes have coverage of around 90%, and are broadcast from the main 81 transmitters.
Because this planning required that all multiplexes move to "mode 3" the post-switchover multiplexes these new descriptions have been widely used to represent the "final" multiplexes, even though legally they are named 1, 2, A, B, C and D - see Ofcom - Multiplex licensees.
Digital UK now refers to the multiplex by the name of the ower, usually four letters, but sometimes the written in full, so we now have:
Multiplex 1 is also known as PSB1 and also BBCA
BBCA denotes the first BBC multiplex when in "mode 3", with all the services from "mode 2" multiplexes 1 and B. This multiplex has many regional versions to supply BBC regional news on BBC One.
Multiplex 2 is also known as PSB2 and also D3+4
The legal owner is "Digital 3 and 4 Ltd", which is half-owned by the Channel 3 licensee, and half-owned by the Channel 4 Corporation. This multiplex has more than 20 regional versions to supply regional news on ITV 1/STV/UTV, plus advert regions for that station, Channel 4, Channel 5 and the channels 3 and 4 "plus one" services.
Multiplex A is also known as COM4 and also SDN
SDN, originally "S4C Digital Networks" was sold to ITV plc in April 2005 for £134m. The SDN multiplex has two versions, one for Wales, where it carries E4 and one for the rest of the UK.
Multiplex B is also known as PSB3 and also BBCB
BBCB denotes the first BBC multiplex when in "mode 6" which is used to carry, by arrangement with ITV/STV/UTV, Channel 4/S4C, the Freeview HD service.
Multiplex C is also known as COM5 and also ArqA (or ArqivaA)
The "mode 3" (now "mode 8") post-switchover ArqA/COM5 multiplex carries all the services on "mode 1" Multiplex C, with space for couple of extra TV channels.
Multiplex D is also known as COM6 and also ArqB (or ArqivaB)
The "mode 3" (now "mode 8") post-switchover ArqA/COM5 multiplex carries all the services on "mode 1" Multiplex D, with space for couple of extra TV channels, which include 4seven and two subscription channels, Sky Sports 1 and 2.
Freeview standard transmission "modes"
The above diagram illustrates the capacity of different ONdigital/ITV digital/Freeview transmissions over the years. The longer the bar, the more bits are transmitted per second. Mode 2 is 16QAM, mode 7 is QSPK, the DVB-T2 modes are 256QAM, the rest 64QAM.
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Tony Sunday 15 April 2012 9:00PM
I am at a loss to know which transmitter I am getting reception from
freq 474000 10 tv no radio
freq 490000 11tv 11 radio
freq 498000 27 tv 3 radio
freq 538000 20 tv 9 radio
freq 578000 17 tv 1 radio
I thought I was pointing to Crystal Palace but am I getting these from eleswhere?
Would be nice to now
Tony: Without more precise information about the location as mentioned by Mark Fletcher I can only guess that, by looking at the frequency information you are currently receiving Mux2 and MuxA from Reigate which were increased in power to 2kW in order to avoid possible interference problems when Rowridge switched over. The other frequencies you mention are all from Crystal Palace.
Intermittent since switch over started we have experienced problems with channels on Mux D / ARQB - Film 4 , Yesterday and ITV4 . All other channels are fine . We are located in RG31 postcode and on the Hannington transmitter .
For example yesterday Sunday 15/4 was particularly bad
We have a roof top ariel which is less than 3 years old and was installed by a professional company. Signal has been fine up until switch over .
We haven't added or moved any VCR , game console or similar device in that period .
Tony: This site and all other documentation works on UHF channel numbers rather than frequencies. To convert from frequency in kHz to channel number, subtract 306000 and divide by 8000. Then round up or down to the nearest whole number - if you have to round up write a '-' after the channel number, if down, write a '+'.
474000 = C21 = Reigate Mux 2
490000 = C23 = CP BBC A
498000 = C24 = Reigate Mux A
538000 = C29 = CP Mux D
578000 = C34 = CP Mux C
My guess is that you have a box with the naive tuning algorithm: just storing the first version of the channels found when scanning from lowest to highest frequencies. The list above is the lowest frequency that each service uses. (You omitted Mux B but most services now live on BBC A.)
If this is the case, after the second stage retune on Wednesday you're likely to get the commercial muxes from Reigate - but perhaps not reliably - and the PSBs from Crystal Palace.
Thank you for your comments and help
I did try to find out whether any of the signals were from caterham transmitter but was not able to see what the frequencies are from that transmitter.
Twin aerial is pointing directly toward CP North of here, caterham is almost in line, if the other signals are from Reigate then these must be coming in at right angles
We receive all the channels [most of the time].
Interesting to see what happens on Wednesday.
David Taylor Thursday 19 April 2012 2:46PM Swanley
Hi guys Post Code BR8 7LH
Haven't been in touch since last year when I purchased a box and got "no signal" message
Now switched over purchased cheap box and installed OK but picture has distortion and sound has hum.Can get all channels and signal says 90%. Tried a couple of different
TVs and scart leads.Have a cheap Freeview TV
which works OK. Should I buy a dearer box ?
Yours Dave Taylor
Hi, I have lost all ArqB/MUX D channels on my digibox since the London switchover. I've tried a first time installation, doing the unplug the aerialcable and scan with no signal etc procedure and still nothing. I am feeling deprived as I have no film4 and yesterday. I live in Central London (W10 6SS) and am hoping the problem will "right itself" but having rescanned a number of times since yesterday morning, I'm not holding out much hope. Any advice would be welcome, ta!
Ami, hi same problem with loss of Film4 and Yesterday but am receiving in GU34 from Rowledge. Looks to me that now post switchover I will have to change aerial or move to vertical polarisation and upgrade coax cable. I thought I was ahead of the game getting digital some time back with freeview NO ONE said that some digital viewers will have to upgrade (Â£Â£Â£) to keep the same programmes. Not good!!!The aerial installers must be working double time.
for some unknown reason just lately
in my area ( b67 5hh )i and neighbours do appear to have lost channel 11 Freeview can you offer any explanation for this
this has happened over the last 2 weeks or so
whereas before everthing was all OK
we are all off the Sutton-coldfieldtransmitter regards john
Hi - p/c GU27 2DG and received local digital (HaslemereRelay) ok until Tues 17th. Lost signal until retuned set Thurs. and then only able to get LONDON service! Complained to Digital.co.uk who put me in touch with the BBC. Appears that when Crystal Palace went full power (sometime around 17/18th and 20kW) as PSB1 PSB2 are on the same frequecies as Haslemere, even though aerial pointing directly at Haslemere R, CP swamping local signal! Have raised complaint and being investigated. Would be nice to get BBC South and Meridian back rather than irrelevant stuff from LONDON !!!
You are right on the edge of (or "was" on the edge of) the Haslemere relay's signal as it beams the main part of its signal in the direction of the town in the valley. Clearly this is no match for the Crystal Palacechannels at your location.
I'm not a great complainer, but as a matter of principle I would probably do in this case. However, I was going to suggest that you raise this matter with your MP, but then I found out who it is...
The predictor at your location reckons that Guildford is the best. A long shot perhaps, but I wonder if it has tuned to that which is off the back of your aerial and that in actual fact Haslemere is still receivable. You may have already have gone along this road, but if not then I suggest that you check.
To avoid the possibility of picking up Guildford, run the automatic tuning scan and unplug the aerial when it gets to 30%.
Then see what BBC and ITV you have by bringing up the signal strength screen. For Haslemere it should be 28 and 22 respectively. It may be 23 and 26 which is CP. If it is, then see if Yesterday is on programme number 12. This is C28 from CP. Similarly look for Pick TV on number 11 which is C22 from CP.
If you find that Pick TV and Yesterday are coming in on 22 and 28, then you know that CP is swamping the Haslemere signals, even though the aerial doesn't face it. If they aren't there, then see if BBC and ITV from Haslemere are in your 800s.
If you manually tune to 22 and 28 and get a signal but no quality, then you know that the two are interfering with one another with no winner.
Hope this helps. As I say, I commend this to you in case you haven't already tried it.
If you do find that Haslemere's channels are in there, then it may need a bit of work to get them under the proper logical channel numbers. I can offer further suggestions should that turn out to be the case.
Thx David Lindsay for your suggstions. Yes is the answer really - I have treid retuning and we do get Yesterday + Pick Tv which initially alerted me to the fact that the transmission wasn't Haslemere R ! Haven't tried disconnecting aerial after 30% so may give that a shot later. And yes, did flag to Digital re raising with MP and joint conclusion was it would be waste of time! One area of hope - Midhurst has 2 relays, Haslemere and Styning. Styning has its freq. changed in Oct (prob due to interference/clashes) so why not Haslemere? tbc.
Mr KN Young: I suspect that the changes to channels at Steyning are to do with the clearance of C61 upwards for mobile 4G use. A number of transmitters are affected and this October seems to be at least one of the times when retunes are going to be needed.
Unfortunately there is no such change due for Haslemere.
One of the issues is that C31 to C37 are being cleared at switchover. This is (or was if the powers that be can make up their minds) going to be used (auctioned off, naturally!) for other TV channels. Consequently, Group A channels that are available for use went from 21 through to 34 to only 21 to 30. As aerials (particularly in the past) tended to be for a particular Group rather than the whole band, most transmitters have kept the same Group (for Public Service channels at least). So now there are effectively less Group A channels available, which is why Haslemere clashes with CP. In other areas, *some* Group A transmitters have some or all Commercial channels (Pick TV, Yesterday etc) out of Group (higher up channels), requiring most people who use them to get a new aerial if they want to watch these channels. As I say, in most cases Public Service channels are in Group.
Even though Midhurst is less than six miles away, you don't have line of sight and from what I can see, the hills that the signal comes over to get to you are covered in trees which isn't good:
I have a digihome pvr (vestel t816) which was fine until the swithover and retune. I have now lost all progs ( film 4, itv4 ect.) on channel 28, and no amount of retuning can get them back. I cant see it being the ariel, as both tv's have tuned to them fine. on a manual scan on pvr of channel 28 from crystal palace - it says no signal. Any ideas ? Thanks
lee: I had a sneaking suspicion that you might have, especially when you knew the chassis used in your PVR, and of course I dare say that you noticed that the channel you cant get is one of the two used by Crystal Palace that has negative offsets on the channel frequency, the other being the HD service which the Vestel wouldn't respond to anyway.
Not sure what the negative offsets you refer to are tbh, I'v got this far with google. Do you recon this model is no good now ? Am trying everything as I like the really simple menu, plus it has saved progs on it, only reason im relectant to buy a new 1. Thanks again J.B.
lee: The negative offset problem is something that has effectively killed off a large number of Vestel chassis PVR's and made others erratic in operation in areas where changes to a transmitters operational frequency had taken place, whereby a multiplexchannel had started transmitting slightly off its recognised frequency so as to keep the standard 8Mhz channel spacing between it and other adjacent channels.
This applies in the case of mux Channel 28- from Crystal Palace, as this is transmitting 167khz under the the proper frequency of 530.000Mhz that Ch28 officially corresponds to, and even although the negative offset isnt that particularly great it still requires a receivers tuner to allow itself be be pulled downwards from its pre-programmed 530.00Mhz, something that the earlier ranges of Vestel chassis cant really cope with by them having a very tight AFC range (automatic frequency control) and are likewise resistant to being pulled down.
This is the main cause of this problem, although the situation was made even worse when the transmitting mode also changed from 2k to 8k at switchover.
The whole thing is similar to a tuning facility that was seen offered in most analogue TVs, insomuch if any channel number was checked on you would always usually see a "fine tune" option being offered, as it was appreciated that bang on frequency isnt always the best for reception (on analogue anyway) and with the fine tune range offered being + / - of a channel numbers centre frequency.
Oh right, most of that is way above my knowledge of tv frequency's ect. , but I understand what you mean reading the comparison with the fine tune and afc. Thank you for your time to explain - guess box is rubbish now then if I want film 4 - shame, because although I'v read a lot of bad things about this model since searching internet for my problem - I have had mine years, it was quite cheap compared to others - and has always worked perfectly, with a nice simple menu and tidy remote compared to others.
Lee: As far as I am concerned, these Vestel chassis PVR's are / were by far the best around for their sheer user friendliness as far as the menu systems offered are concerned and quite a delight to use compared to some Humax's, albeit that the latter is undeniably technically superior, and although I have three Humax's (one a FoxSat HDR) my wife always prefers to use the Vestel T825 (Hitachi branded) that I also have coupled up rather than my Humax 9200 (one of) purely for the menu reasons mentioned.
Should be thinking along the lines of purchasing a new PVR, then a modern Vestel chassis PVR that has thankfully retained about 90% of the original classic menu system (and only menu system) is being sold by Argos, and is a Hitachi model 325 PVR with a 320Gb hard drive, and a model which I haven't (as yet) had any adverse reports about, friends of mine having purchased two of these PVR's just over two months ago now.
Although I dont suppose I should have mentioned that, as its tempting fate as far as Murphy's law is concerned.
Nice one JB - I have now found this update > 5.7 2008-11-18 15:18:58 OAD / RS232 30 seconds Fixed support for negative UHF offsets used with 8K COFDM mode (previous versions may fail to pickup channels on multiplexes switched to this mode after digital switchover) <
Worth a try? I will take a look at the Hitachi if that fails. Thanks again for your time.
Lee: If you have the facilities to be able to download the software then transfer it into the Digihome then by all means give it a try, its just that I generally dont mention that procedure as its total hit and miss as to whether or not it works, because if a tuner has a tight AFC capture range then in my book the problem really isnt completely cured except by replacement of the tuner, which to my knowledge anyway is not available as a spare part.
I would though appreciate if you can give an update on the results should you decide to try the procedure mentioned, and "if" successful if you could also mention the serial number of your PVR, as subtle changes to the circuitry are always linked to serial number ranges.
Yea will do , am going to try it, will be later in the week as I don't have a laptop with a com port, and will be getting a local pc shop to do the transfer for me, rather than using a usb to rs232 adaptor.
lee: Good news then! although I would have liked the serial number associated with your model of box so that I could tag it as being from a serial number onwards that the update works on, as subtle changes to a devices circuitry always takes place during long batch runs, and with this in many cases being why an update will work on some models but not others even although the model to all intents is the same.