All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
roy in southend: London switchover completed last Wednesday and Anglia switchover completed last July.
So either:
1. you are tuned to an Anglia transmitter (probably Sudbury) even though the aerial faces London (Crystal Palace), or;
2. you have been incredibly slow at retuning, or;
3. your block of flats have two aerials (one on Sudbury and one on Crystal Palace) which are combined and fed throughout the building's distribution system. This would give you the choice of reliable reception of either region.
Some receivers, when they encounter signals from different regional transmitters, present the user with a menu with those regions. It is often the case that there is only a single aerial which is directed at one transmitter. Therefore selection of any region other than the one of that transmitter may be liable to poor reception because the aerial was not intended to pick it up. The same thing happened in the days of analogue and would usually result in a poor picture.
As for Crystal Palace vs Sudbury, the former uses low channel numbers and the latter's are higher. During the automatic tuning scan, Crystal Palace is picked up below 30% and Sudbury is above. So unplug the aerial lead during part of the scan, to avoid the respective transmitter's signals.
| link to this comment |
tim: If the receiver is overloaded with signal, then the signal strength readings will be likely to be misleading.
That is because the circuitry is overwhelmed by the signal, it can't function normally.
The fact that there is an initial blip of 18% and then nothing could give rise to the theory that the signal level is too high.
Try putting less signal into the TV. For example, remove the aerial lead and hold the plug close (a centimetre or so away). The aim is to loose a bit of signal. Bear in mind that the receiver may take 10 or more seconds to adjust to your change, so wait.
Or as I said above, try removing the outer part of the plug (if it's a screw-together one).
When you do this, observe the signal strength meter and see if it increases.
| link to this comment |
Nick: Refer to the list of BBC DAB transmitting stations for its national multiplex:
BBC - Help receiving TV and radio - Transmitters
Aldeburgh is 1.8kW, Mendlesham is 4.3kW, Manningtree is 5kW.
DAB multiplexes are single frequency networks. That is the BBC national multiplex, for example, is on channel 12B nationwide. So between two transmitters the signal received can be the sum of both, or indeed you may have the sum of three.
The pros could perhaps suggest whether a directional aerial is better. I suspect that an omnidirectional DAB aerial may be best for you.
The other thing you have to contend with is that not all services are available from all transmitters. The BBC as a Public Service broadcaster usually has the best coverage. So it is available from Aldeburgh transmitter whereas the commercial national multiplex ("Digital One") does not broadcast from this site.
Then there is the question of what site(s) local/regional broadcasters use. According to tx.mb21.co.uk Aldeburgh DAB is BBC national only, and Mendlesham and Manningtree carry BBC national DAB services, as well as the Digital One one.
This page on Wikipedia suggests that there are no local/regional services in Suffolk:
Digital radio in the United Kingdom - Wikipedia, the free encyclopedia
You would be best advised to check to be sure this is right.
However, what it does mean is that you have no idea of where any future local and regional DAB broadcasters might site their transmitters. Thinking this way makes me think that you need an omnidirectional DAB aerial providing that it is sensitive enough to pick up BBC national and Digital One. If you can get these DAB services at ground level with a portable radio, then I would say definately go with an omnidirectional DAB antenna.
| link to this comment |
Nick: For technical parameters of all UK radio transmitters (including DAB), download the spreadsheet here:
Ofcom | Tech Parameters
| link to this comment |
James Bright: Your receiver has a mind of its own.
Where receivers find signals from more than one transmitter they put the duplicate channels in the 800s.
Evidently yours is one of those that knows better than the user and moves things around as it pleases. Look through the settings to see if there is an option that you can turn off to stop it from doing this.
Come Blue Bell switchover, you may find that this won't happen because its signals will be stronger. Crystal Palace completed switchover on Wednesday and so its digital signals are now much stronger.
If your box allows manual tuning, then I would run the automatic tuning scan through with the aerial unplugged so as to blank out what's stored. Then manually add the six multiplexes from Blue Bell.
| link to this comment |
I Pike: Ensure that your receiver is tuned to Rowridge for these services. Go to ITV3 and bring up the signal strength screen and check that it is tuned to UHF channel 25. Likewise for Yesterday it is C28. Pick TV is C22.
If you are tuned to Rowridge, then you may benefit from switching your aerial to vertical.
The Public Service channels (BBC, ITV1, Channel 4, Channel 5 etc) are at a transmission power of 200kW horizontally and vertically. The Commercial ones (ITV3, Pick TV, Yesterday, Film 4, Dave etc) are 50kW horizontally and 200kW vertically.
| link to this comment |
I Pike: I should also point out that the three Commercial channels use the same frequencies as Stockland Hill and Crystal Palace, so depending on your location they could be the cause of interference.
On Wednesday when the Rowridge Commercial channels changed channels, the power of Stockland Hill went up, and Crystal Palace's came on air at its switchover.
Without knowledge of your location, I can't know how likely this might be that it is interference.
Switching your aerial to vertical should help with that if it is. It will be two-fold:
1. A stronger signal.
2. Greater rejection of the unwanted signals as they are horizontal only.
| link to this comment |
tim: Where a signal is split using an unpowered splitter (i.e. no amplification), then it stands to reason that the strength of the two outputs must be less than that of the one input.
However, where an aerial lead "loops through" a device, the signal is amplified to counteract the loss caused by splitting it.
| link to this comment |
Monday 23 April 2012 4:54PM
Sean: A communal aerial system such as that in your building is usually the responsibility of the landlord. So if it found to be faulty, then the organisation or person responsible should have it fixed.
However, based on what you've said, I'm not sure that you have done anything that would tend to suggest that the fault lies with the aerial system.
Would I be right in saying that your flat has one aerial socket (e.g. in the lounge) and you wish to feed a TV in another room from it as well as the lounge TV?
The first thing to try is connecting the TV/box that is adjacent to the aerial socket on the wall directly to it and seeing if the problem clears. If it does, then this would tend to suggest that it is something to do with your internal wiring.
Is the three way splitter a powered one or not?
What sort of reception did you get before switchover? Did you have the splitter connected whilst you had good reception before switchover (if you ever had good reception before switchover)?