All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
MF: Based on what I've seen on here, some viewers using Hastings transmitter may be affected by others co-channel and may have to change transmitter.
I'm not an aerial installer so the following are just my thoughts as technically-minded anorak on this subject.
If your aerial is a Group A one (bottom third of the band), then it will be unsuitable for Heathfield as it is now Group B (middle third of the band).
If you are looking at DIYing or just wish to be informed, then I recommend that you look at www.aerialsandtv.com
There is a page on Heathfield, although the recommendations still say it is C/D, which is what it was before switchover:
Heathfield Transmitter
You appear to have quite good line of sight (*with no local obstructions such as trees or buildings*):
Terrain between ( m a.g.l.) and (antenna m a.g.l.) - Optimising UK DTT Freeview and Radio aerial location
The transmitter is 14 miles away. I looked on Streetview and St Mary's House and neighbouring tall building looks as though they could pose a problem. It may vary from house to house what can be picked up and what can't.
Dover looks out of the question.
The only other thing I can suggest is that you may be able to mount the aerial such that your house or some other object acts to block the signal from Eastbourne. This in so doing probably means putting the aerial somewhere where it is likely to pick up less signal from Hastings.
Mounted on one side of the house might help. Or in the loft where you can construct some sort of shield with chicken wire and tin foil. I've no idea how effective this might be, particularly as other buildings may reflect the Eastbourne signals back towards the front of your aerial (depending on which way you face).
The COM channels use a less robust mode (less error correction) than the PSBs and this is so that they can cram in more services, so they are going to be the first ones to go, even without the noise from Eastbourne.
It is worsened by the fact that they are both vertically polarised, although the stronger the signal the more it can be picked up by an aerial of opposite polarisation.
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Matt: The answer to your question depends on which transmitter that you are using.
Based on the fact that you have lost Dave and Viva as well, then I gather that you are receiving from Hastings transmitter. The reason is due to the local Eastbourne transmitter (which doesn't carry these services) using the same channels as these services from Hastings.
If it is possible to receive from Heathfield, then that is what you may have to do in order to receive the full complement of channels. Should you do this, then you should be aware that the SDN multiplex which carries ITV3, QVC and others is on low power until 27th, so you may not be able to pick it up until then.
As I said to MF, Hastings uses Group A channels (bottom third of the band) and Heathfield uses Group B ones (middle third), so if your aerial is a Group A one it will be unsuitable for Heathfield. A wideband one should be OK though, although the older the aerial, the more likely it is to be a Group A one.
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John Langley: C46 is now on full post-switchover power and the rest remain on their pre-switchover "low" power.
Based on the readings you have given, I am wondering if you live in a strong signal area, or at least your aerial is providing a very strong to excessive signal, the latter being a possibility for C46 now and for the rest when they go up on 27th. Without knowing your location, it isn't possible to get an idea of how likely that might be the problem.
What stands out to me is that for the high-power multiplex on C46 you only have a strength of 46, yet 24 and 39, which are still on low power, are in the 80s. With the low-power signals you have ample strength so I suspect that the low strength reading for C46 is because it is excessive and requires reducing.
42 and 45 are close to 46, so perhaps latter the high power signal is acting to desensitise your receiver when it is tuned to the formers.
This can be likened to walking down the street at night. When car headlights come towards you, your eyes become desensitised making it more difficult to see the relatively dark surroundings.
If you have a booster (and it is not used to split the signal to different rooms) remove it. Once you've done that, if the problem prevails, you may need attenuation to bring the level down even more.
You may find that as you reduce it, not only will the strength of C46 go up, but the quality of 42 and 45 will improve.
For a more in-depth explanation see ukfree.tv - independent free digital TV advice
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Andy: Retuning on or after 27th should be expected to restore these channels.
If your set has manual tuning, then manually tune to UHF channel 48 which is what these services are currently being broadcast on.
If you have a booster, then it is probably best removed. This may or may not help with your reception of COM5.
Once the booster is removed, if you got nothing tuning to C48, then try again.
Different sets work differently and have different sensitivities, so it might be worth trying each one (if they allow manual tuning).
As far as signal strength goes, it isn't so important; it is quality that matters. So the objective is NOT to get the strength bar as close to 100% as possible; indeed this could indicate too much signal strength.
For this reason I suggest removing the booster. So long as the quality is excellent, then the picture will be the best will ever be.
Different sets use different scales, so don't go comparing expecting like for like readings with the same aerial.
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Colin: Let us know how it goes.
I can see the contours on the map and from the satellite images they have trees on them which could be a problem. They may be a problem all the time or just at some times, such as when they're wet, blowing about or when they have leaves on. Or, having sorted the problem with C28, you may be lucky and never encounter poor reception.
Try to get C28 tuned in, even if this means taking the aerial and moving it, perhaps on the first floor or even outside in the garden. Each time, do a manual tune on C28. Logically, it would seem a good assumption that the further away from the bottom of the decline you are the more chance you are of picking it up. Try moving in that direction (going into the garden if necessary). Whilst moving it, try and view the strength and quality of the other multiplexes to get an idea of where the best and worst spots are.
The COMs (25, 22 and 28) use a less robust mode of signal, so a poorer signal makes them more susceptible to break-up than the PSBs (24 and 27). I have no idea to what degree that might affect things, but maybe being mindful of this might help identify "not-so-good-spots".
Different receivers have differing levels of functionality and usefulness for the DIY aerial installer. Some give little away, maybe having a single scale for both strength and quality. So look at the receivers you have and find the one or ones that give the most information and use it/them for your testing.
Once you have C28 tuned in and it has added the services on it (Yesterday etc), then don't retune as the tuning is correct.
Try to logically discount things. So if the cable runs down from the loft to the lounge and you keep going down to the lounge to look at the set, then disconnect the cable from the aerial and attach a short piece to which you connect a TV to see what you get.
If you then get something on C28, keep it connected like that whilst you site your aerial to best effect. Then turn your attention to the seemingly faulty downlead. Maybe try the old aerial as well and see which works best.
I should point out that if you have a distribution amp for feeding multiple rooms, then disconnect this whilst you're trying to get your aerial to work. It could be a problem caused by the amp.
If you have a mast-head amp, then trying with and without and with varying levels of amplification (if there is such a setting) might be worth a try.
Always be mindful that you could have too much signal and be looking to test the theory.
An aerial's gain in one direction comes about at the expense of sensitivity in other directions. So to have more gain, there is more loss of sensitivity in other directions. So a higher gain aerial tends to have a narrower angle of acceptance.
If you live within line of sight of the transmitter, but a long way away such that when the signal gets to you it is weak, then obviously gain on the narrow beam from the transmitter is what you want.
But the lower you live down a drop, the more you are trying to pick up a less focused signal. If the brow and the slope have trees on, then they will be moving about changing the signal. Thus an aerial with narrow acceptance angle may be what you don't want in such circumstances.
As I say, I'm not a professional but I've seen this explained and it makes sense.
I cannot say whether this is or is not of importance in your case. Clearly the fact that you are close to the transmitter helps more than if you had been further away.
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jo: You should attempt manual tuning.
BBC standard definition and radio = C50
ITV1, C4, C5 etc = C43
HD services (if applicable) = C40
For those you have, see that they are tuned to the above channels by viewing the signal strength screen.
A more specific idea of your location may help be more specific. For example, if you are close to the transmitter, your signal might be a bit high and in need of reduction.
Also, you "may" be able to receive from another transmitter that carries all the Freeview channels, albeit that you will probably need another aerial.
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John Langley: Due to the fact that the pre-switchover digital signals were weaker, some aerials have been replaced with higher gain ones. Plus the fact that with some transmitters, including Bluebell Hill, some pre-switchover digital channels were out of the native analogue group.
Bluebell Hill was Group E for four-channel analogue which covers the top two thirds of the band. All but two of the pre-switchover digital channels are in Group E, but two are below it (in the bottom third, aka Group A).
Sensitivities drop off gradually, but the fact that the weaker signals are out of group would have been likely to cause issues for some futher away. Wideband aerials may have been fitted so as to pick up the two Group A channels.
Oh, and there is no such thing as a "digital aerial" ! I presume you have a wideband aerial.
After 27th, all Bluebell's channels will be within Group E, with only one being outside of Group B (middle third) and at that it is only one channel outside, so Group Bs will probably work.
For an explanation of aerial groups, see Aerials, TV Aerial and Digital Aerial
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I digress.
What you don't know is if the overloading is occuring on the input of the distribution amplifier or the input to each TV or a bit of both.
If the signal on the input of the amp is too high for it to cope with, then it stands to reason that the outputs will be distorted. No amount of attenuation of the outputs will right the problem and no amount of reduction of amplification will right the problem.
So you need to go to square one and see what sort of level you have from the aerial by connecting directly to it.
You "may" find that there is that much signal that you replace the powered amp with a non-powered splitter.
If you still have your old aerial (the one that you replaced the current high gain one with), then that may be suitable. All channels are in group and the signal strength will be on a par with the former analogue that it used to pick up.
For more information on this subject, see www.aerialsandtv.com
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John Langley: You can pick attenuators up of sites like eBay. ATV also sell them.
I personally find that, since Maplin went onto the high street, its prices tend to be high and that the stuff it sells can be obtained for less from online sources.
It's good practice to use F-connectors for connections that are perminant (so to speak) such as in the loft. Use coax connectors for behind the TV set.
Some attenuators have coax connections, some have F-connectors.
To connect a TV directly to the aerial, connect the cable from it to one of the output feeds to one of the rooms. Bear in mind that there will be a certain amount of loss in that cable; that is the signal coming out of the cable into the TV will be lower than that coming out of the aerial cable (in the loft) and going into the feed to the room where the TV is.
You could take a TV into the loft and try it directly.
And/or reduce the level of amplification if it has a control on it. See if this rectifies the problem.
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Simon Holland: The situation with Heathfield is that COM4/SDN remains on low power until 27th.
For a full list of Freeview channels, see this page:
DMOL Post-DSO Multiplex Channel Allocations
It's those with a bullet in the "E" for England column that apply.
Which group(s) are you missing?
If you are missing COM4 and your receiver has manual tuning, then try tuning to UHF channel 48.
If you have a booster, then remove it. Try again tuning to C48.
If, having removed the booster, the other channels have good quality, then leave the booster out. Only if you find issues with weak signal and poor quality should you consider installing the booster, although it's not forced to fix it.
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Thursday 14 June 2012 11:52AM
Tony: HD is not broadcast from Bluebell Hill or Dover before switchover. Both these will complete switchover on 27th when their HD multiplexes will come on air.
Looking at the predictor, Rouncefall is roughly off the back of your aerial and its HD channel is C47, so you could try manually tuning to it until 27th. I don't have first-hand experience of HD receivers, but I understand that when manually tuning some, such as Humax, you have to specify DVB-T2 mode, which is that used by Freeview HD broadcasts. If you don't then it probably defaults to DVB-T which is what Freeview standard definition services use.
I suggest that you use the booster if it can be seen to be of benefit. With digital reception you need enough signal to be above the threshold for your TV to resolve a picture. Signal levels vary over time, e.g. due to the weather, so the signal level needs to be high enough above so that any drop won't put it below. Where this is the case, then the expected result is that reception (availability of channels) will be hit and miss.
The signals after switchover are stronger, so after 27th try removing your mast-head amp. You may also try Dover.
What you aerial is best suited to depends on its type. Bluebell Hill will be all Group B, except for ArqB which will be just outside, so a Group B aerial will probably work. Dover is C/D. Crystal Palace is Group A. If your aerial is a wideband then it will work for all, although wideband yagis aren't as sensitive on Group A channels. If you want to know more about this, see ATV's site www.aerialsandtv.com
In particular these may be of interest:
Aerials, TV Aerial and Digital Aerial
Gain (curves), Again
Television Aerial Boosters / Amplifiers, Splitters, Diplexers & Triplexers
Bluebell Hill Transmitter
Crystal Palace Transmitter
Check that your receiver is tuned to the desired transmitter as sometimes they don't. There are six multiplexes after switchover and one service from each is: BBC One, ITV1, BBC One HD, ITV3, Pick TV and Yesterday. Check the signal strength screen to see that each are tuned to the correct UHF channels for your chosen transmitter.