All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
LSB1302: I believe it's most likely that your aerial is pointing to Belmont, and it's probably a 'Group A' type designed for RF channels 21-35. The first four analogue transmissions are between channel 22 and 32, so aerials installed before Channel 5 started will usually be Group A. Channel 5 is on C56. Most of the digital multiplexes are at higher frequencies, channels 48-66. You need a wideband aerial, which covers C21 to C68, to get all the channels.
At switchover, the public-service multiplexes move down into Group A, but some of the commercial channels will still be at higher frequencies, and you'll still need a wideband to get all of them.
When joining aerial cables, you should always use a proper coaxial cable connector. You can't just twist the conductors together. If you're trying to feed two TVs from one aerial you should use a proper splitter rather than connecting the two cables directly to the aerial.
| link to this comment |
Paul: A UHF aerial is a UHF aerial, wherever you are. There is no such thing as a digital aerial. Some of the massive constructions that people think of as 'digital' aerials are made by Televs, a Spanish manufacturer.
Gain and bandwidth are two different properties of an aerial. For a given number of elements, a narrower bandwidth provides higher gain. You usually get best results from an aerial that just covers the frequency range you need.
I'd recommend getting a local installer to select and fit a new aerial. They should know what range of frequencies is being broadcast, at what power, by the local transmitter and therefore what aerial is most appropriate.
| link to this comment |
Peter Chick: Currently, ITV Central East on satellite is encrypted, and therefore only available if you have a Sky box and Sky viewing card. Sky sell a 'free-to-view' card for £25 if you already have a dish and box, or charge £175 for dish, box, card and installation.
BBC One East Midlands is free-to-air on satellite, so it's available on Freesat and Sky.
For terrestrial TV you'd need to point a TV aerial to one of the Central East transmitters. If you provide a full postcode, we can see if that's possible for you, or whether the terrain prevents it.
| link to this comment |
Andy: Yes, there are engineering works, but they relate to the aerial that is currently providing analogue signals. It will be the digital antenna after switchover. There may be occasional periods of low power on digital if they have to climb past the digital antennas, which are below the main antenna at the top of the mast, but I believe all the necessary installation and cable connection has been done.
The old antenna was replaced at the end of last year and I believe it's now back in service, though my aerial points to Crystal Palace so I can't be sure.
I've run a prediction for Watertower Way (RG24 9RF), which appears to be on the estate. It's relatively poor - no coverage predicted for multiplexes B C or D, variable for multiplexes 1 2 and A. However, about 500 metres away on Barton Place (RG24 9JS), it gives a prediction of good reception. The predictor may be using the permitted radiation pattern rather than the actual. Your postcode, RG24 9TG, is about another 500 metres to the south-east, and here there's no prediction for multiplex 1, 2, C or D, and very poor for multiplexes A and B. The predictions do *not* account for any engineering work.
Basically, the problems get worse the closer you are to Guildford, which is the interfering transmitter.
For best results, the aerial should be fitted outside, with lots of clear space around it to reduce reflections from the buildings. The developer may have fitted an aerial in the loft, or a communal system, to reduce the visual impact of the aerials if the site is considered sensitive. If the aerial is in the loft, complain: they just don't work as well as they do outside.
| link to this comment |
Frank Ryan: You only need to connect HDMI *or* SCART - you don't need to connect both. Both HDMI and SCART have 'select' signals that the box signals when it is on - the TV watches for a change in these signals and switches to that connection. With both connected it may not consistently choose one of them. I would recommend disconnecting the SCART cable since it only carries standard-definition pictures.
To display HD pictures on some channels or programmes via the HDMI cable, the box and TV must negotiate Content Protection (HDCP). This is basically the TV promising that it *is* a TV, and not a recorder that you could use to distribute copies of the content. If it fails, the box shuts off the HDMI output. I believe it has to periodically re-negotiate, and some TVs don't do it properly. Switching off the TV and/or the box and turning it back on often sorts the problem out. Alternatively, try a different cable.
There are reports that HDCP may not work consistently with long HDMI cables. Ensure that the cable is only as long as it needs to be.
| link to this comment |
Kevin: If you're currently getting BBC, ITV and Channel 4 free-to-air, the dish should already be pointing at the correct satellites. You then just need a Sky box.
If you want to keep your FTA box and use it in another room, you would need another run of cables from the dish - you cannot split satellite dish cables.
| link to this comment |
Charles Stuart: The whole point is that the frequencies can't be used outside the radiation patterns shown here, because they would interfere with other stations. Channel 29 from Crystal Palace is restricted at about 300° to protect Ridge Hill (West) near Hereford - this is the service that points roughly south-east to serve Cheltenham and Gloucester with West-region news rather than Central. Crystal Palace is over the horizon 112 miles away, but in the right weather conditions, signals can bounce off the atmosphere and cause problems.
In the north sector from 325° to 35°, it has to miss the coverage area of the Waltham transmitter, the main transmitter for the East Midlands 100 miles away. It has to avoid affecting the relay sites' ability to pick up their signal from Waltham as well.
It might just be acceptable if a station on the other side of the target city used the same frequency, aimed back towards the main station, and broadcast simultaneously with it - a Single Frequency Network. Receivers are already designed to handle reflections, and they just treat extra transmitters as really big reflections, as long as all 'reflections' arrive within a short period of time.
However, they're trying to keep the costs down by piggybacking on the existing main transmission facilities. Power would have to be pretty low as well, where the radiation patterns are restricted on both sides of the city.
These diagrams aren't final. A large number of sites have to be retuned after switchover is 'complete' to free up channels 61 and 62 for 800MHz (4G) mobile phones. The rough plan is to move use of 61 and 62 to 49 and 50, and use of 49 and 50 to 39 and 40, which were previously going to be released in the Digital Dividend. The plans they were based on weren't finished anyway - final plans for Tyne Tees and Ulster are still yet to be published.
The diagrams also represent the restrictions that must be placed on the signal - it won't be permitted to broadcast outside this area. However, it is not possible to build practical aerials that exactly match these patterns, so the actual broadcasts will be even further restricted.
| link to this comment |
katie: We really need a full postcode to give complete detail in most cases, but Lincolnshire is pretty flat so it's quite likely that you're using the Belmont main transmitter. Alternatively, you could be using the Waltham main transmitter, though this is less likely. Do you get Look North from the BBC and Calendar from ITV, or BBC East Midlands Today and ITV Central Tonight?
Looking at the frequencies, it's much more likely to be Belmont, as that uses high frequencies for most of the digital multiplexes - up to C68 for Mux A, which is right next to the mobile phone frequencies.
Belmont switches over at the beginning of August this year, and Waltham at the end. You could just see how well it works once switchover is complete - some channels will be moving to lower frequencies, and all will increase in power substantially.
| link to this comment |
Colin: The predictor here doesn't have the detailed terrain information or the radiation pattern information that the broadcasters' predictor has. Try the Digital UK tradeview link next to your post.
In this case the problem is that this website assumes omnidirectional transmission, while in fact it appears that the digital aerial array points north-west to fill in the west side of Salisbury itself. It uses four log-periodic aerials in an array to restrict the radiation pattern to a fairly narrow beam.
It could be that the main aerial is used as well as these four smaller aerials and there is an omnidirectional component. The published documents don't say, and the radiation pattern for Salisbury was redacted from Brian's Freedom of Information request.
At switchover, digital services move to the omnidirectional aerial at the top of the tower, but there's still a problem
At your postcode, it shows that your best bet for a full 6-multiplex service is actually the Mendip transmitter (West region). The prediction is for 'marginal' or 'variable' results though. You might get slightly better results from Rowridge (vertical polarization) on the public-service multiplexes, but worse results on the commercial multiplexes. It's likely that it won't work a lot of the time, though, so you may want to consider getting Freesat or Sky.
| link to this comment |
Monday 21 March 2011 5:42PM
Reading
richard: The hills at Long Law and Horseshoe Hill are in the way. You're in a fairly deep valley, where transmissions from the main transmitters don't reach. The Rookhope relay transmitter is your only option for Freeview, once it switches over - currently it only transmits analogue signals. It will be a Freeview Light transmitter at switchover, relaying the public-service multiplexes from Bilsdale.
The switchover date has not yet been set - we currently expect some time in September next year.
For a greater range of channels, or to get them sooner, consider Freesat.