All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
Colin Mason: As ATV says, RF is a black art. See the conclusion at the bottom of this page:
Loft and indoor aerial installations for TV, FM and DAB
Prediction of reception is more a guide to likelihood of success and should be taken with a pinch of salt. Such systems exist not because they can ever be anywhere near accurate, but because of the demand for such solutions.
The Digital UK Postcode Checker predicts the percentage of the postcode that is "served" and that which is "marginal". This in itself means a very large area when you consider the area where your aerial is. The predictor does not take into account local objects (trees, buildings etc) and is theoretically based on a particular aerial.
I'm not saying that in some cases the predictor isn't useful, but it should be remembered that it has its limits.
It is possible that your reception may be variable, perhaps being better at certain times of year. For example, vegetation that may be in the way may affect the signal.
The only thing that is a certainty is that anyone with an aerial on the Romaldkirk transmitter will only get the Public Service channels.
I would wait until 26th September to see what you can get.
After switchover, the Commercial channels (those that don't broadcast from Romaldkirk) use a less robust mode so as to allow them to cram more services in. This is in effect like them being more fragile.
With digital, quality is more important than strength. A strong poor-quality signal will mean break-up or non-existant pictures.
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MARGARET MARTIN: The answer to the question would depend on which transmitter the new aerial is directed at.
I should say that there is no such thing as a "digital aerial". Aerials are designed to pick-up particular frequencies. In some cases a different aerial is required for digital reception because the frequencies used are different to the former analogue.
As Peter Henderson says, Digital UK does predict "good" reception on all channels from Divis now. However, such predictors should always be taken with a pinch of salt as there are other factors not taken into account.
I had a look down your road on Streetview (photos taken August 2008) and most houses have two vertical aerials (or did then). They would appear to be pointing at Black Mountain and Clermont Carn (for RT, TV3 and TG4). I spotted only one horizontal aerial on Divis.
This leads me to think that reception from Divis is difficult because there is no line of sight to the transmitter on the top of the hill. Furthermore, I should think that if you can get any digital from Divis now (bearing in mind that it's on much lower power than after switchover), then you're lucky!
It would appear that the only two transmitters north of the border that you can receive (if at all) are Divis and Black Mountain:
- If your new aerial is on Black Mountain then it will be vertical and pointing a bit anti-clockwise of west. This does not carry any digital (Freeview) now and after switchover will only carry Public Service channels (these being all BBC TV (standard definition and high definition), BBC radio stations, UTV, UTV+1, ITV2, Channel 4, Channel 4+1, Channel 4HD, E4, More4 and Channel 5 (I assume UTV HD if there is such a channel).
There should be no need to replace aerials on Black Mountain as the channels (frequencies) used after switchover are the same as those used for the current analogue. Only where viewers change transmitter (probably to Divis) to get the full service will a different aerial probably be required.
- If your new aerial is on Divis then it will be horizontal and pointing roughly north-west. Divis broadcast all Freeview channels after switchover, unlike Black Mountain which will be "Lite".
The fact that you can receive one of the multiplexes suggests that your new aerial is probably pointing at Divis. If not, then you must be receiving it with the aerial not pointing at the transmitter and with the aerial vertical when the signal is horizontal.
If your aerial is on Divis, then all you can do is try manually tuning missing channels (if your receiver allows). The rigger has installed the aerial based on the signals that can be received now. You will have to hope that the boost in power in October will be sufficient. I'm not sure whether you have recourse with him if it's not because he can't know for certain whether the aerial will work come October. For this reason it would perhaps have been pertinent to have the aerial changed after switchover.
By the way, the changeover will happen in two stages. On 10th October BBC standard definition services will go on full post-switchover power. These will take the place of BBC Two analogue. BBC One, UTV and Channel 4 will continue to be available on analogue.
Two weeks later on 24th October the other analogue channels will go and the other digital ones will go on full power.
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Cara: Your most likely transmitter would appear to be Shotleyfield as that is where all the aerials I can see on Streetview are pointing. Shotleyfield is to your west and your aerial will be vertical (elements up/down).
The Shotleyfield transmitter is a relay or "filler-in" for an area that can't receive from the main transmitter, Pontop Pike. That is not to say that you are definately in such an area (they do overlap).
Shotleyfield currently broadcasts only the four analogue channels and after switchover will carry digital (Freeview) Public Service channels only and these are BBC standard definition and high-definition TV, BBC radio, ITV1, ITV1+1, ITV1HD, ITV2, Channel 4, Channel 4+1, Channel 4HD, E4, More4 and Channel 5.
The Commercial channels, which carry such as ITV3, Pick TV, Yesterday, Film4, Dave and 4seven, will not be broadcast from Shotleyfield (ever) because their operators do not wish to pay for the transmitter, and this is also the case at over 1,000 similar relay sites.
In "some" cases it is possible to receive from a full-Freeview transmitter, usually with a different aerial. Where this isn't possible, viewers will be stuck with Freeview Lite.
Ultimately only an installer can tell you whether it is possible to receive from Pontop Pike. The Digital UK predictor reckons that there is a "good" chance of doing so after switchover. However, such predictors should always be taken with a pinch of salt, particularly in locations such as yours where you can't see the transmitter due to the terrain.
I suggest that if you decide to call in an aerial installer (with a view to receiving from Pontop Pike) that you don't do so until after switchover on 26th September when all channels will be at their full post-switchover power. This is because the installer needs the signals to be available, on the air, in order to decide whether it is possible to receive them. If you have one install an aerial for Pontop Pike now, you may have no recourse with the installer should the subsequent post-switchover signals not be receivable.
Pontop Pike is to your east and aerials will be horizontal (elements flat). It might be worth looking around to see if anyone is receiving from Pontop Pike.
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Michael Pickles: First and foremost, it is good practice to have the receiver tuned to the transmitter to which the aerial faces. Bilsdale and Emley are in different directions, so at least one must be wrong.
The transmitter that a TV tunes itself to during the automatic tuning process is not forced to be the "right" one for the aerial. Thus, in some cases it is necessary to tune manually or carry out some other workaround in order to get the right transmitter. Not doing so can mean poor reception.
When one encounters "no signal", however tempting, it is usually advisable not to retune because this simply results in the tuned channels being wiped from the memory.
Only in cases where changes have been made at the transmitter end should retuning be carried out. If it turns out that the TV has suddenly "forgotten" the tuned channels, then this tends to indicate a fault with the device.
On the basis that the problem exists with two receivers, it would appear that they are not at fault. By retuning you have compounded the issue by erasing the tuning information from the receivers' memories.
If the Bilsdale analogue signals disappeared, then this perhaps suggests something with your aerial setup. How is the signal distributed? If it is a powered amplifier then it may be at fault. You should try bypassing it by connecting the feed from the aerial directly to a feed to one of your TVs. You will, of course, then have to carry out a retune once you have done this (because you wiped the memory).
If your aerial points to Bilsdale, then bear in mind that its digital signals are still pre-switchover and therefore low power. They may be weak or non-existant at your location. Contrast that with the Emley digital signals which will be as strong as the former analogue (because it has switched to digital and Bilsdale hasn't).
If your aerial points to Bilsdale then can you not receive from Emley or another transmitter that carries Yorkshire programming? The fact that you can do so even though the aerial faces the wrong way (assuming it points to Bilsdale) suggests that this may be a possibility.
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Adam Rodriguez: I wonder if the guy may be right if your aerial is pointing at the Llanelli transmitter which carries Public Service channels only.
Refer to this page for services by multiplex (those with a bullet in the "W" for Wales column apply):
DTG :: DTT Services by Multiplex
There are six multiplexes, each of which is a single signal which carries multiple services. In summary there is:
PSB1/BBCA | BBC One, BBC Two etc
PSB2/D3&4 | ITV1, ITV2, S4C, Channel 4, Channel 5 etc
PSB3/BBCB | BBC One HD, BBC HD, ITV1HD, S4C Clirlun
COM4/SDN | ITV3, QVC, bid etc
COM5/ArqA | Pick TV, Dave, Really etc
COM6/ArqB | Yesterday, Film4, 4Music etc
The Public Service Broadcaster (PSB) channels are carried by all transmitters. The Commercial ones (COM) are only carried by the main transmitters and large relays. This means that there is a portion of the population that is unable to receive the COMs (some of which may have them intermittantly).
You say that you have logical channel numbers 1 to 5 which means that you must be receiving PSB1 and PSB2. If your set isn't a HD one, then you won't be able to receive PSB3 even though it is available. I conclude that it is the COMs only which you are having difficulty with. Is this correct?
You've posted on the page for the Llanelli transmitter and it is PSB-only. So if your aerial points at it, then you are receiving what it broadcasts and therefore the gentleman is quite correct. From your location the Llanelli transmitter is north and your aerial will be vertical (elements up/down).
If your aerial points to Llanelli and the TV has tuned in the COMs, then these must be coming from another transmitter which is likely to be in another direction to which the aerial faces and so this is liable to result in poor reception (of those channels). Based on the Digital UK predictor, I wonder if it is the case that your aerial is on Llanelli, that the COMs your receiver has tuned in are those of Kilvey Hill which is a full-Freeview transmitter and is also vertically polarised.
Or if your aerial points to Wenvoe (a bit clockwise of east, aerial horizontal), then this is also a full-Freeview transmitter, but its COMs broadcast on the same channels/frequencies as the three PSBs from Llanelli, so you may find that reception of the COMs is wiped out thanks to that.
Or you "may" be able to receive a full service from Carmel which is clockwise of north, with your aerial horizontal.
Find out which transmitter(s) your receiver is tuned to for each multiplex by viewing the signal strength screen whilst on one of the services.
Those that "may" be available to you are:
- Llanelli: PSB1=C49, PSB2=C45, PSB3=C42
- Kilvey Hill: PSB1=C23, PSB2=C26, PSB3=C29, COM4=C25, COM5=C22, COM6=C28
- Wenvoe: PSB1=C41, PSB2=C44, PSB3=C47, COM4=C42*, COM5=C45*, COM6=C49*
- Carmel: PSB1=C60, PSB2=C53, PSB3=C57, COM4=C54, COM5=C58, COM6=C61
* Wenvoe's COMs co-channel with Llanelli's PSBs.
For example, tune to ITV3 and bring up the signal strength screen. ITV3 is carried on COM4, so if it says that it is tuned to UHF channel 25 then it is coming from Kilvey Hill.
There is no guarantee that you can receive from any of the other transmitters. Even reception of the COMs off-beam of the aerial isn't forced to mean that an aerial pointing in the correct direction will result in reliable reception of those channels.
My money is on your aerial being on Llanelli and the three COMs being tuned to Kilvey Hill.
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sue: There may be a number of transmitters that can be received at your location. Check that it is tuned to Ridge Hill (if indeed that is where your aerial points). If it is, then maybe you should consider using another transmitter such as Bromsgrove or Sutton Coldfield because they appear as if they "may" be better bets at your location.
To check that you are tuned to Ridge Hill, select BBC One and bring up the signal strength screen. If it is tuned to Ridge Hill, then it will say that it is on UHF channel 28. Other possibilities that it could be tuned to are:
- Bromsgrove C26
- Sutton Coldfield C43
- Kidderminster C49
- Malvern C53
Do the same for ITV1. Ridge Hill is on C25, or it could be tuned to:
- Bromsgrove C23
- Sutton Coldfield C46
- Kidderminster C58
- Malvern C57
If you find any tuned not to Ridge Hill (assuming that your aerial faces Ridge Hill), then this needs correcting. The automatic tuning scan runs from UHF channel 21 to 69, so if gives only a percentage, then you can convert.
All Ridge Hill's channels are in the 27s, so unplug the aerial at about 30% and you will miss out all the 40s and above. So if, for example, you find that it is tuned to Sutton Coldfield instead (on 43 and 46), then this trick with unplugging the aerial will avoid that. If it's tuned to Bromsgrove, then that's more tricky as both the wanted and unwanted channels are interleaved in the 20s so you may have to resort to manual tuning, if available.
If in fact your aerial points at Sutton Coldfield, then perhaps it has tuned elsewhere. This may happen because other transmitters are found first. In which case, start the scan with the aerial unplugged and plug in at 30% and unplug again at 55%.
The above (checking that it's tuned to the correct transmitter) is always the first thing to look at. If it turns out that it is, then it could be co-channel interference caused by the weather. This occurs where signal(s) on the same frequency(ies) from distance transmitters are carried to your location. (That is the "same frequency(ies)" as your desired transmitter uses.).
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Jonathan C: As you have a reception issue, knowledge of your location, preferably in the form of postcode or nearby postcode (such as a shop), is really needed (postcode district is not specific enough). It would also be useful to know which transmitter your aerial is pointing at. If you don't know, then knowing your location, along with the direction of the aerial, and whether it is vertical (elements up/down) or horizontal (elements flat, as would have been the case for your Crystal Palace aerial).
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Michael Pickles: When you do get it working, if your receiver does default to Bilsdale during its automatic scan, you should be able to avoid this by having the aerial unplugged for the first 30% of the scan.
This is probably not an issue now as Bilsdale is still on low (pre-switchover) power. It switches next Wednesday and Wednesday 26th.
From that point, the digital signals should be of equivalent strength to that of the current analogue. As analogue receivers sometimes default to Bilsdale, so "may" digital ones, although it probably depends on how each "decides" which signals to go with having completed the scan.
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Michael Pickles: I wonder if you have a masthead amp as well. This will require a separate power supply which could perhaps have failed (or the amp itself has failed).
This may be built in to the distribution amplifier (the one with multiple outputs).
An amplifier with no power to it will give nothing out. That's what makes me wonder if you have a mast-head amp that is now acting as a block for the signal (either through failure of itself or its power supply).
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Monday 3 September 2012 12:20PM
Eric Armstrong: There should be no need to adjust your aerial for reception from Eston.
"If" you are to ever receive the Commercial channels (ITV3, Pick TV, Yesterday, Film4, Dave etc) on terrestrial, then you will have to receive from Bilsdale. I say "if", because it may not be a given given Roseberry Topping is in the way.