All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
Dennis : So does the BT Vision box tune correctly to Bluebell Hill or is it giving Anglia?
You've already given the answer to your question: you're in a difficult reception area for Bluebell Hill and Crystal Palace.
Looking at the OS map, in the direction of Bluebell Hill the ground rises up towards Starmore Wood. Whilst the Anglia transmitters are further away there is probably a clearer path between you and them.
If your aerial was on Crystal Palace then I would suggest unplugging the aerial after your TV has scanned its channels as they are all in the first third of the band, with Anglia's being in the middle third. Unfortunately those of Bluebell Hill and Rouncefall/Sudbury (the transmitters which broadcast Anglia together on the same channels) are interleaved.
If your TV has manual tuning then why isn't it allowing you to do it? What is the result?
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Robert Walker: You are correct. The analogue signals were switched off in Ireland on 24th October 2012.
Judging by Streetview photos of Donegal Town centre, aerials are horizontally polarised and pointing south south west, which by my reckoning means they are pointing to Truskmore transmitter. This broadcasts Saorview on UHF channel 53, so if your TV has manual tuning try a scan of C53.
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LouiseB: By resetting you are simply deleting what is stored and then carrying out a scan of what is available. As the channels ceased to be available to you before resetting then how can the act of resetting ever make them available?? The answer is that resetting will only result in loss of the channels from the receiver, or them coming back, in which case they would have come back anyway because the receiver will give you the best picture it can for the signal being fed into it.
I wonder why you aren't using Bluebell Hill, which would also give you BBC South East and ITV Merdian, rather than their London variants from Crystal Palace. The only thing I can think, other than maybe you prefer London news, is that the hospital is in the way.
I suggest that you don't have line-of-sight to Crystal Palace. I can't say with absolute certainty, but I think the brow over which you are receiving is somewhere around Shorne Wood Country Park. Anything on that brow that might change, such as trees, and anything that is in or near the line-of-sight that changes could affect your reception.
I then looked at the satellite image your area, as published by Google. To the north of the hospital, in the direction of Crystal Palace is a field which has outlines of roads. It looks as if there is a development which has appeared since the photograph was taken. If this is the case, and buildings have gone up this year then there must surely be suspicion that this is the cause for anyone experiencing degrading TV reception from Crystal Palace to the area's east.
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LouiseB: Looking at your street, there are going to be few, if any, locations where reception from Bluebell Hill within the loft "might" be a possibility.
The row of houses are in line with the signal! That is, the houses run a little clockwise of being north to south and the signal is coming from just clockwise of south.
It's likely that the signal path will be through a neighbour's roof space and that's aside from the question of whether there are trees and other obstructions in the way.
The hospital and trees around it quite clearly cause difficulty with TV reception from Bluebell Hill as the houses which are closer to it tend to be using Crystal Palace.
Quite frankly, I think that you have been lucky to have ever been able to receive Crystal Palace with a loft-fitted aerial, bearing in the mind that you are low down with higher ground in the way.
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Anna: If this happened when you put your box into standby then perhaps it is because it doesn't have enough memory to store the channels. The fact that it is ITV/C4/C5 etc, which is found last during the scan, could perhaps mean this is a possibility.
See here for an explanation I gave to someone else the other day (also on Winter Hill):
Most popular questions | ukfree.tv - 11 years of independent, free digital TV advice
The point is that it hasn't (if indeed this is problem) run out of memory because it can't handle all the channels from Winter Hill but because there are other channels its picked up from other transmitters. You need to prevent it from picking up some of those others so as to have room for what you want it to store. It's a bit like not eating too much before lunch and then not having enough room for the main meal.
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LouiseB: You don't have line-of-sight to the transmitter. The effect is that there are spots where one or more signals (frequency/ies) is/are good and where one or more aren't so good. The objective is to site the aerial where all are good.
Because (apparently) an object has changed that is in the path of the signal, one or more signals have changed. This is not an unusual effect - both that the change has caused a change in reception and that not all frequencies are affected to the same degree.
The irony is that if you go to the science department of the Academy, they should be able to explan what might have happened!
The point I alluded to in the first paragraph is that radio waves (signals) travel in straight lines. You can't "see" the source (Crystal Palace) because there is high ground in the way. Consequently, you are relying on the waves bending around the obstruction, which is the brow of the hill.
Different frequencies bend differently - that is they scatter differently. The result is that in the "shadow" of the hill there are spots where one or more is good and others aren't so. Thus, in the shadow there are less places where good reception can be had on all channels.
Now, if you understand that, consider the effect that a building might have. It might be a bit like the brow of the hill, as far as effect on the signal goes; it might affect one or more frequencies and others get away pretty much unscathed.
In your case you may have both these effects together (as far as Crystal Palace goes at least). The more of this that you have, generally speaking (even the professionals say all of this is a black art), the more you could have issues.
The point is that the (apparent) change in the building has resulted in a change to the signal.
The rain on the building perhaps changes how the building affects the signal. For example, maybe it reflects it in a way that acts more to your detriment.
What you might do is try moving the aerial along the loft to see if there is a spot that gives better reception.
The reason aerials are put on rooftops is because that is the place where the clearest view can be had, where there is the least chance of objects being in the way. This goes hand in hand with trying to reduce the degree to which signals being received have been bent and therefore scattered by objects.
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LouiseB: I think that your difficulty with Bluebell Hill is caused by a combination of the hospital and the fact that the houses run in line with the signal. It's likely to be a waste of time if, on pointing the aerial at Bluebell Hill, it's being directed through a neighbour's loft space.
At least with Crystal Palace the house is perpendicular to the signal path (from the transmitter).
If your aerial is Group A (red tip) then it isn't so suited to Bluebell Hill. Group A is the bottom third of TV frequencies. Bluebell Hill's channels are Group B, which is the middle third.
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Anna: Your follow-up posting means that what I suggested in my posting at 10:17pm isn't the issue.
I am not sure what else to suggest; maybe others can chip in.
I do note, however, that there are mobile phone base stations 1km away to your west, which is the direction your aerial is facing. The other fact is that ITV/C4/C5 from Winter Hill is on the highest channel which is just below any 4G signal operating in the 800MHz band.
That said, the signal from Winter Hill would be expected to be strong, which counters to some degree any likely interference. In any case, 1km is quite a distance, I would have thought (although I'm not the expert in radio signals).
Maybe if you have an amplifier (booster), particularly to split the aerial feed to more than one room, this could be affected.
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Friday 1 November 2013 8:39PM
David Parker: As a Yorkshireman I don't have any insider knowledge. The Emley Moor page says July 2014.
I imagine that Briantist has taken this from a recognised source.