All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
Martin Engwell: There are 101 reasons why the picture on one multiplex is affected and not on another.
Digital reception is more an "all or nothing" system rather than analogue whose picture varies relative to the signal.
Take signal level for example. There is a threshold over which the signal level must be in order for a receiver to resolve a picture. Providing that the quality is good, then the picture will be exactly the same as if the signal strength were higher (but not above being too high such that it overwhelms the receiver).
Thus, a reduction in strength will not have any effect on the picture unless the reduction is greater than the amount that the level was above the threshold.
A reduction in strength with an analogue picture is likely to have some degree of detriment to its quality but may still be watchable.
Because the quality of a digital picture isn't analogous to signal strength, then the effect (or lack of) on the picture is therefore not necessarily the same as that on the signal.
So you could perhaps find that if you used the appropriate test gear that the signal level on all channels has changed but that this has only adversely affected the resolution of the pictures on the BBC mux.
Another factor is that not all channels will be exactly the same. As they propagate they will be reduced and refracted to different degrees.
It is possible that they are using the reserve antenna which is further down the mast and as such the path or line between it and you may be different and importantly there may be other objects that are affecting your reception that wouldn't otherwise do.
I said that there are 101 reasons; these are just a few possibilities. The length of the aerial cable and differences in the receivers are two others.
I'm not a professional, but I would certainly not dismiss mounting the aerial outside as then the signal will not be reduced and refracted by the roof which might be helpful. The professionals do say that reception is a black art, so "common sense" of increased height doesn't always pay off.
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Pauline Colman: This sounds like some sort of interference generated by some noisy electrical appliance/device, perhaps in your house a that of a neighbour.
The fact that it happens at the same time suggests that it is something that is timed, although it could be something that is manually switched on by the user, just at the same time.
A noisy pump or motorised valve on a central heating/hot water system could be a possibility. Try turning such things off when it occurs to discount them as possibilities.
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bob: It's great to hear that you have the missing channels now and that it all came good in the end.
It is always the thing that you don't know whether and perhaps don't expect that the signals will improve at a later date. It turned out to be worth waiting rather than opting to incur expense changing the aerial, with such expense possibly only really being necessary in the mean time.
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Ian Humphreys: There are some "self-help" relays and information from Ofcom is here:
Ofcom | Self-help TV Relays and Digital Switchover
Maybe your MP would be able to help.
Is it really the case that hundreds cannot have dishes fitted? They could of course go above the roof-line on a pole, possibly on the chimney or if not, fitted to a side-wall with a mast.
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P. Kieran Ward: The EPG information for all Freeview channels is carried on all of them. Therefore if you are watching BBC, for example, the EPG information for ITV and Channel 4 will still be available.
Clearly it won't be available across the two platforms: Freeview and Saorview.
From what you describe, your receiver doesn't "take the initiative" and "look" for the EPG information on any other multiplex other than the one that it is currently tuned to.
I'm not a professional so don't know whether there is a way around this. On reading comments online, the Humax devices are well designed, so if they won't do it, then maybe nothing will do it.
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louis feather: At just over half a mile I would expect that the signal from the Idle transmitter will be plenty strong enough. If anything, your receiver could be suffering too high a signal level rather than too low a level.
Confirm that it is tuned to Idle for all signals and that you aren't watching the output of another transmitter such as Emley Moor. Do this by checking the signal strength screen whilst on each of the following:
BBC One=C24
ITV1=C21
BBC One HD (if HD model)=C27
ITV3=C42
Pick TV=C45
Film4=C39
Can you not see the transmitter from your house? With line-of-sight you certainly shouldn't be expected to have a problem.
Too high a signal level can overwhelm the receiver and as a result, it can start to indicate too low a signal level and poor quality. Sometimes this will cause the strength and quality meters to jump up and down.
See:
Freeview signals: too much of a good thing is bad for you | ukfree.tv - 10 years of independent, free digital TV advice
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MEM: Because the DAB signal and the TV signal are different signals. The TV switchover didn't mean any difference to DAB radio.
See:
Digital Radio Ireland » Can I get DAB
Maybe you need a directional aerial.
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Adrian: Have you done a full reset?
I understand that the transmission power of CC went up at switchover, so could you have too high a signal level now? If so, this may likely show as too low a level or no signal.
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Frustrated new mover : That is odd. Have you identified the 7 rooms that it serves and are you sure that the room in question isn't one of them.
Do the dish feeds run from the loft or could one be fed from the loft? The cable used for satellite is ideal for Freeview as well, it is just the plug that might need changing or a suitable adaptor fitting.
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Friday 9 November 2012 11:29AM
Keith: The sensitivity (gain) of an aerial isn't the same across all UHF channels/frequencies. For yagi aerials, the shape of the curve is broadly the same. See here for examples that illustrate my point:
Gain (curves), Again
The gain of wideband yagi aerials on Group A channels is much lower than C/D ones. That is why there is no such thing as a high gain wideband aerial that has "high" gain on Group A channels.
More gain in one direction is simply at the expense of more "loss" in others. So the "beam" of a higher gain aerial is narrower.
If your wideband aerial is sufficient for Clermont Carn, then there is no reason not to continue using it. The reason for suggesting use of a Group A aerial for Divis is because of the lower gain of the wideband aerial on its channels and the poor reception you are experiencing.
You need a diplexer to combine the two feeds:
Online TV Splitters, Amps & Diplexers sales
For Divis and Clermont Carn, get a diplexer that "splits" at C38. This will allow you to receive a multiplex from Divis on C36 should it ever come to fruitition.