All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
Ken Campbell: I write on here as a technical bod rather than an aerial installer.
An aerial amplifier (booster) without any power going into it usually gives nothing out. Where the signal going in is very strong then a little signal might come out.
Therefore, in order to test without the amplifier it must be removed from the feed. It could be, and indeed it would be best, that you have a masthead amplifier (i.e. one that is close to the aerial - with only a short piece of cable between it and the aerial) in which case the box, perhaps behind the TV, into which mains electricity flows is merely a power supply which feeds the amp adjacent to the aerial. So turning it off, or even removing it for test purposes, still leaves the amplifier connected.
A look at your road on Streetview (photos taken June 2012) shows it to be a new development with few TV aerials and some satellite dishes. Indeed, the only TV aerial I spotted is on number 48 and judging by the photo it appears to be little above the apex of the roof.
I then placed myself on Marcroft Road near to the end with Tir John North Road and observed that Marcroft Road slopes downwards, so the roof line of that house and quite a few others are likely to below those I'm stood next to.
With that in mind and with the fact that you are at the bottom of a drop which is causing difficulty with reception from Kilvey Hill, I wonder if, as well as getting the aerial up as high as possible, having it sloping upwards a little might be worthwhile, this assuming that the bracket allows.
With digital reception there are two factors: strength and quality. Quality is digits all present and correct so as to allow the picture to be built up. A small (low strength) signal of good quality can be made bigger with an amplifier. A poor quality signal of any magnitude cannot be made better with an amplifier. See here for an explanation:
Television Aerial Boosters / Amplifiers, Splitters, Diplexers & Triplexers
A high gain aerial has a narrower acceptance angle because its gain (increased sensitivity in one direction) comes from having less gain elsewhere. That is, if it were used to send out a signal (transmit) it would emit a narrower more concentrated beam than one of lower gain:
Aerials, TV Aerial and Digital Aerial
Where there is no line-of-sight such as because one is at the bottom of a slope which blocks view of the transmitter, there is obviously no beam to focus on (signals travel in straight lines). Consider car headlights coming towards you but which are not visible because there is higher ground between you and them. Over the brow you can see light and if the light were brighter it would light where you are because it bends at the point it meets the brow. Such a situation would be like sunlight which lights all parts of a room, even though not all parts are in direct line-of-sight to the sun.
Now remember the points about digital signal quality and the fact that higher gain aerials have narrower acceptance angles. These aerials are therefore looking across a narrower angle and therefore rely on the quality across that (narrower) angle being good. If there is a momentary drop in quality across that angle, the quality of the signal going down the lead will dip. If, however, a wider angle of viewing is available, that drop in quality may be across a smaller proportion of the total angle, hence the average quality of the signal (that which goes down the lead) doesnt drop as much. The signal level may be lower, but an amplifier can improve that. This is why in situations such as yours that an aerial that isnt high gain accompanied with an amplifier is better. Indeed, one of the experts on here suggests a log periodic (rather than a yagi) with an amplifier can be effective:
Aerials, TV Aerial and Digital Aerial
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James Town: You posted previously about this and myself and MikeB made some suggestions:
Resolve your interference problems | Freeview Interference | ukfree.tv - 11 years of independent, free digital TV advice
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Richard: The bearing is 232 degrees.
However, in order to use a compass you need to take into account the fact that Magnetic North and True North are different. The former varies over time and by location.
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Helen Rankin: Where does your aerial point? South west to Black Hill or east to Craigkelly?
Judging by Streetview photographs Black Hill is generally used in your area. If you are using Craigkelly then you may have difficulty receiving all channels, judging by predictions.
Further advice on reply.
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How come the local TV channel from Rowridge will only be broadcast horizontally? Whilst many will have their aerials horizontal, vertical polarisation is surely favoured for new installations and so all channels should be available vertically.
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Helen Rankin: The first step when retuning is for what's been stored previously to be deleted. So it's not so much a case of them being lost, but rather that they aren't found again when receiver scans for channels.
Digital reception relies on the signal level (strength) being above a particular level (threshold). Signal levels vary slightly due to atmospherics and the like. Thus, the likely answer is that the level has dipped a little.
If the receiver has manual tuning then I would use that to try and restore the other channels. For Craigkelly channels are:
COM4 - ITV3 - C42
COM5 - Pick TV - C45
COM6 - 4Music - C39
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john layton: I don't think you have any worries about having too much signal at your location.
The pixelation could be down to not having line-of-sight with the transmitter, something which you can't do anything about. The terrain means that the northest edge of Norfolk has difficulty or cannot receive from Tacolneston, which is why there are a series of relays along the north coast.
As far as aerial groups goes then if you have a Group C/D aerial, strictly speaking the three COM channels on 42, 45 and 39 are "out of group" and therefore your aerial isn't as sensitive to them as the PSB channels. That said, it might be good enough for the COMs, in which case the gain on the PSBs is a bit greater than the minimum required.
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Kevin Wright: I suggest that the ongoing engineering works might be the cause, and indeed anytime Belmont is on low power you could, potentially, not be able to receive it.
The Digital UK predictor doesn't think you will get reception from Belmont, except "poor" for the HD multiplex.
However, it predicts good coverage by the Sheffield Crosspool transmitter. I guess you might be using Belmont because Crosspool is out of the question.
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rod tucker: No, because you aren't in a location where the Commercial multiplexes are available.
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Wednesday 6 November 2013 1:01PM
JR: Because the signals are being picked up from a full service transmitter, the most likely being Crystal Palace.
Crystal Palace is on a bearing 49 degrees anti-clockwise of Woolwich and it broadcasts horizontally rather than vertically.
Looking at Streetview there is a mixture of the two on Abbey Road.
Many communal aerial systems are filtered so as to only allow through channels used by the transmitter in question. This is evidently not the case here.
You should be able to confirm where the channels are being received from by viewing the signal strength screen for the following:
PSB1 Woolwich=C60 | Crystal Palace=C23
PSB2 W=C57 | CP=C26
PSB3 W=C53 | CP=C30
COM4 CP=C25
COM5 CP=C22
COM6 CP=C28