All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Ed Blythe: "digital powered aerial"? That sounds like an indoor aerial device. It never works well with digital television - the signal drops too much as it travels through the walls and too many reflections occur.
You always get best results with a properly installed roof-top aerial.
Things might improve for indoor aerial use after switchover.
Digital UK's postcode checker actually says you should get best results from Bilsdale at that postcode.
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Steve: the problem is that the received signal level naturally varies over time, due to the changing weather conditions.
Because the indoor aerial is much lower in height it's blocked more by neighbouring buildings, and picks up more reflections from them, as well as reflections within the building. It tends also to have poorer gain, front/back ratio and cross-polar rejection compared to a roof aerial, meaning it picks up less of the signal you do want and more of the interference you don't want.
Amplifiers can never correct for picking up unwanted signals, they amplify unwanted signals just as much as wanted ones, and they add extra noise and distortion of their own. An amplifier might help if the signal level from the aerial is actually weaker than the minimum the TV or box needs, but generally they're harmful.
As I said, the signal level from any transmitter - and this includes unwanted signals - varies over time. The prediction is done on the basis that you will get problem-free reception 99% of the time. That's still over three-and-a-half days - 87 hours - per year. You might get good reception with an indoor aerial some of the time, but you'll get a lot of interruptions too.
Because most TVs and set-top boxes don't show the signal AND the noise level, only a raw signal strength, it's really not possible for the average user to work out the best site for an aerial.
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M
Olivers Mount (North Yorkshire, England) Full Freeview transmitFriday 7 January 2011 7:02PM
Reading
Neil Rowntree: that depends on the transmitter you're using.
For analogue TV, Olivers Mount is an relay of Emley Moor, for ITV and C4, and of Belmont for BBC One and Two (it receives the transmissions off-air and retransmits them).
Digital TV is fed via satellite and it's up to the broadcasters to decide which feed is transmitted. At switchover, Olivers Mount will continue to be fed independently rather than off-air - it appears in all documentation as the lead transmitter in its own transmitter group (it will have one relay, Hunmanby).
If you're currently getting Tyne Tees news, your aerial is probably pointing at Bilsdale, or one of its relays. Or, your box has tuned into Bilsdale rather than Olivers Mount: this can happen if the signal from Bilsdale is strong enough to be detected and the box stores the first version it finds, rather than the strongest/best quality signal. Bilsdale uses much lower frequencies than Olivers Mount.
You might want to see if you have another version of ITV1 somewhere in the 800s, and if that's less prone to breaking up than the version at 3. If so, next time you retune (next Thursday, to get ITV1+1), consider unplugging the aerial before you start rescanning, then plug it in when the search reaches about half-way through.
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Maurice Deaton: there will not be any test transmissions from Waltham before the DSO2 date. There are no frequencies available for testing, because all the frequencies are already in use at multiple sites.
A few sites have had HD transmitters set up before switchover, to cover the largest cities (e.g. London, Birmingham, Yorkshire, Newcastle, Glasgow and Edinburgh - Manchester and Liverpool have already switched), but most of these have had to run at lower power than the rest of the digital multiplexes, with correspondingly poorer coverage areas. They've had to run at lower power to avoid conflicting with other sites using the same frequencies.
HD service starts from Waltham on the 31st of August 2011, when all analogue services are switched off.
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Mr Sizzle: anything's possible, but it's highly unlikely to have a significant effect. That is, I can't think of any electrical properties of sausages that would cause a change in the properties of the aerial.
If a person touches an indoor aerial, they provide a route for electrons to flow to ground. (This is the same as why you shouldn't stick your fingers into an electric socket or touch overhead cables with a stick.) This changes the properties, which is why a seemingly-well-positioned indoor aerial can stop working when you let go of it. Your string of sausages might have an effect if it touched the ground, but otherwise? No.
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M
Backwell (North Somerset, England) Freeview Light transmitterWednesday 12 January 2011 2:58PM
Reading
Kevin: most likely your TV is 'HD Ready', indicating it can accept HD input from another device, rather than fully 'Freeview HD' compatible, able to decode DVB-T2 transmissions.
This confusion is unfortunate, but has come from the industry wanting to suggest 'future proof' sets without knowing that the regulators would require a different standard to be used when HD services started.
What's the TV's model number?
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roger barrow: the BBC's HD channels are number 50 (BBC One HD) and 54 (BBC HD) in the EPG, if you have a compatible TV and it's properly tuned in.
Most likely your TV is marked 'HD Ready'. This means it can handle HD input signals from other equipment. However, most such sets were designed and manufactured before the standard for HD in the UK was finalized, and the final spec is not compatible. It must have the 'Freeview HD' logo to tune into HD broadcasts.
You will need a separate HD set-top box or PVR to receive HD broadcasts.
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Michael Mulvany: not for the foreseeable future. The commercial channels don't see enough benefit in extending their broadcasts to the 1,000-odd relay transmitters, and they are not required to do so. Unless they change their minds, the answer is 'never'.
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M
Nottingham (Nottinghamshire, England) Full Freeview transmitterMonday 17 January 2011 9:59PM
Reading
Ian: I wish Brian would take down Mux 7 and 8. They were only hypothetical, possible assignments in an Ofcom study on 'interleaved spectrum'. Some sites had two possible frequencies, some had one.
They're not licensed to anyone, Ofcom haven't even set a date for auction of any frequencies, so we're a long way from knowing if there will even be a service and what frequencies it will be on.
At some sites, these two erroneous bits of data are actually hiding real allocations, although usually temporary ones.
Since the study was done, European countries have collectively decided to flog off channels 61 and 62 (about 800MHz) for mobile phones, which means the whole thing has to be replanned anyway.
PSB3, or BBCB, will be the high-definition multiplex after switchover. The BBC's other services all move to BBCA, which gains 6Mbit/s, one-third, extra capacity over Mux 1. This isn't really enough for all their services, but the BBC have closed most of the services that wouldn't fit.
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Thursday 6 January 2011 2:02PM
Reading
Ann: Mux 1 is 16QAM 3/4, Mux 2 is 64QAM 2/3. Mux 1 provides the majority of BBC channels (BBC Four/CBeebies are on Mux B), Mux 2 carries ITV1, C4, Five and a few associated channels.
The raw signal strength means pretty much nothing. If two people are talking quietly at the same time, the overall volume level might be the same as someone talking loudly, but you won't be able to work out what either of them are saying. What's important is the level of interfering signals, and that depends on where you are and whether the signals are reflecting - echoing - off any surfaces between you and the transmitter.
The signal levels are always subject to 'fading' - changes in the air pressure, temperature and humidity affect how the signals travel through the air, just as fog affects transmission of light (which, after all, is just another electromagnetic wave, just with a much higher frequency). It can affect different frequencies by different amounts, or the transmitter causing interference on one frequency may not use the other frequency at all.
Digital UK's predictions are made on the basis of the known variation in fading and the predicted signal levels arrive at a given point from all transmitters in their system. It actually predicts no service from any transmitter for you at the moment. You should get best results from Rowridge (vertical polarization) after switchover in 2012. The predicted coverage from Midhurst is poor.