All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Thomas: One of the reasons for switching to the 8K mode, from 2K, for the SD multiplexes at switchover is that it is more robust to certain sorts of interference. The HD multiplex is transmitted using the new 32K mode in DVB-T2, so if you're suffering from narrow-band interference or from impulse interference, the HD mux may well handle it better.
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Bruce Manning: The DUK predictor is showing poorer performance on Mendip PSB muxes from August, because they use the same channel as Waltham's will when it switches over.
I would think your aerial is likely to have better directional properties than the model used for the calculations, so you could certainly try it and see.
The aerial would need to be aimed fairly accurately, as the Carmel transmitter in south-west Wales also uses these frequencies.
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Richard Nickinson: Stockland Hill has transmitted HD signals since April 2010. This multiplex is at full power.
Please see What does "Full HD Ready" actually mean? | ukfree.tv - independent free digital TV advice . If you're sure you have Freeview HD equipment, see Single Frequency Interference if all the other multiplexes are working reliably.
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Stewart Crowe: The BBC have made a change to flip between interlaced and progressive modes for different content. http://www.bbc.co.uk/blogs/researchanddevelopment/2011/04/software-upgrade-for-bbc-hd-on.shtml
Some TVs aren't handling it well. Sony may be developing an update to fix the issue - your best bet is to contact them.
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g.evans: All PSB multiplexes are at full power (180 kW) but only BBC A is currently transmitting from the main antenna at the top of the mast. D3&4 and the HD mux are transmitted from the reserve aerial, about 37 metres further down the mast. For some people, terrain will block line-of-sight to the reserve aerial but not to the main antenna. I wouldn't expect this to cause a massive difference in reception, though.
I've seen claims that this is to protect analogue services at Rowridge, but BBC A on C27 would clash with Rowridge ITV1. I suspect it's more likely that they're trying to protect Reigate Mux 2 and Mux A, and possibly Bluebell Hill Mux 2, although C27 clashes with Bluebell Hill Mux A.
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R Gagen: Why not charge once for both switchover days? You can find simpler guides for some boxes at TV Re-tune . Over-75s can contact the Switchover Help Scheme at
The Switchover Help Scheme can help you make the switch to digital TV. | Switchover Help Scheme
At your local transmitters, there will be two late channel changes at Sudbury. Tacolneston adopts final channels at switchover step 2. However, the HD multiplex is assigned C62 which is now due to be released for mobile phone services. This channel will have to change - hopefully they will get the plans sorted out before November and it can start up on the newly-allocated channel.
Most of the information is on the web, but you can subscribe to receive updates to Digital UK's ALmanac if you're a Registered Digital Installer, Associate RDI, or a member of the CAI. Go to Transmitter Network - Digital UK Almanac for information.
If you don't have the necessary credentials, you can just check that website periodically. However, some documents don't seem to be appearing there that should be (e.g. the 3-month-out documents for STV Central aren't there).
'NEW 7' and 'NEW 8' are possible frequency allocations for future services which may or may not ever start up. It's very unlikely that they will start before the main switchover programme completes, and probably not until after the 800MHz (C61 & C62) clearance is completed. Displaying them on this website is premature.
Also note that these were the *widest* possible channel allocations, covering the largest area from that transmitter - local TV services might get different allocations just to cover the target market.
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John: The diameter of the tube is more likely to make a difference than the material. See Aerial and Satellite Pole Tests for some tests.
Another major factor will be the wind loading of the aerial itself. Generally speaking the X-types and tri-booms have a higher wind-loading than plain-rod Yagi aerials, and the more elements, the worse affected. Looking at the prediction for your location, you shouldn't actually need a particularly large aerial - unless you're feeding more than one TV from the same aerial, I would start with a small log-periodic type. Anything much bigger and you're likely to have to add an attenuator to reduce the signal levels after switchover.
You can see a list of estimated wind-loadings for some aerials at ATV`s Choice Of Aerials for digital TV .
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Ken C.: While Nottingham and Waltham are in the same direction, Nottingham transmits on vertical polarization rather than horizontal, as Waltham does. Aerials are designed to reject signals from the opposite polarization - Digital UK's predictor allows for 16 dB of rejection, most practical aerials have more than this.
Nottingham's radiation pattern is concentrated to the south-east of the transmitter, attenuated by 7.4 dB (over 80%) in your direction. It's also much lower power than Waltham. On top of that, it looks like there might be terrain blocking line-of-sight.
Digital UK's postcode checker offers a number of alternatives, but Nottingham is not one of them. It is actually indicating that you might have a problem with SDN and ArqB multiplexes after switchover. It predicts a six-multiplex service from Emley Moor. Still, if you're getting reliable service from Waltham now, you may be OK after switchover (it's showing no prediction for any Waltham multiplex, except for Mux 1).
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Lang: H.264 and MPEG-2 describe how the picture is compressed to reduce bitrate. The DVB-T and DVB-T2 standards describe how to carry the data making up the picture and audio over the air.
DVB-T2 is a revised version of the DVB-T standard, using a greater number of carriers (32K rather than 2K/8K), a larger number of amplitude levels and phase offsets (256 rather than 16 or 64) and different error-correction algorithms that waste fewer bits.
DVB-T2 was finalized in late 2009, after the T260HD had already been on sale for a year. Using it allows the broadcasters to squeeze four HD channels into one 8 MHz radio channel, where France - which uses MPEG-4 with DVB-T - only manage to fit three (and those three at a lower bit rate than Freeview HD).
In addition, for copy protection, the EPG data on Freeview HD is compressed/encoded with proprietary encoding tables which are only available from the Digital TV Group upon signing up to their copy-protection scheme.
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Wednesday 27 April 2011 12:33PM
Maureen McKinley: Brian is wrong, all three commercial multiplexes moved to their final locations this morning.
You need to do a factory reset, also called a first-time installation or a default setting, on your box, to ensure that it isn't remembering the old location for the channels and ignoring the new one. Do whatever you did when Wenvoe originally switched over at the end of March last year.