All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
John Hearnshaw: Unfortunately 4seven won't be available from the Calver Peak transmitter because it is carried on one of the Commercial multiplexes which don't broadcast from there.
It will be available on Freesat:
What's new? - freesat
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Mike Summers: With the except of Heathfield, the other three possible transmitters at your aunt's location are within 22 degrees of one another and all broadcast vertically. Hence her receiver could easily be pickup up the wrong one.
At 274 degrees is the Newhaven relay which only broadcasts Public Service channels and did not carry Freeview before switchover.
At 284 degrees is Whitehawk Hill which is adjacent to Brighton Racecourse and carries all Freeview channels and had low power Freeview signals before switchover.
At 262 degrees is Rowridge on the Isle of Wight which serves a large chunk of the south coast. It was horizontally polarised only before switchover and now transmits horizontally and vertically.
If your aunt's aerial is vertical and pointing at Whitehawk or Newhaven, it could be picking up Rowridge a bit now, seen as it broadcasts vertically.
I had a look down the road and I see that they are bungalows and therefore are lower down, so it might explain the need for amplifier. A few aerials are horizontal and thus on Rowridge. Others are vertical and could therefore be on Newhaven or Whitehawk.
If you're tuning the TV, then connect it straight to the aerial to tune it(via the power supply for the amp). That way you know that the DVD can't be causing any problem.
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cjh: It may be the case that Buckland (known as "Dover Town") is a better signal for you, which is why the aerial is directed to it.
In the days of four-channel analogue, all transmitters carried the same four channels. Main high power transmitters like those at Hougham (known as "Dover") cover large areas. Unfortunately their signals don't get everywhere, primarily owing to the terrain.
Because the ground slopes downwards towards the sea, reception from Dover is difficult to impossible, which is why the small "filler-in" relay transmitter at Buckland was installed. This is sited in a location where it can receive from Dover and where it can be "seen" by the area that has difficulty receiving from that main station and this is so that the area can receive from it.
It carried all four analogue channels and was therefore not inferior to the service offered by Dover.
Post switchover there is a two-tier terrestrial transmitter network. There are two types of broadcaster: Public Service ("PSB") and Commercial ("COM").
The four analogue channels had and still have a "Public Service" obligation (as does Channel 5) and they are now carried from all transmitters that carried four-channel analogue in the past, as this includes Dover Town.
However, the COMs don't have a "Public Service" obligation. They operate solely for their own benefit; i.e. to turn a profit. They transmit from 81 of the largest transmitters (largest by viewer population) and this includes Dover. This gives them coverage of 90% of the population.
They were asked if they wished to increase their coverage and they declined. For them to transmit from the 1,000 or so small relays like Dover Town would roughly double their cost of transmission whilst only adding 8.5% of the population to their potential viewer-bases.
When their objective is to get as many viewers as possible at lowest possible cost to show them advertising (which they sell), it's not hard to see why they don't wish to invest in the relays.
As Mark Fletcher says, a more specific location is necessary. Looking at the contour lines in the CT17 area, likelihood/difficulty of reception from the main Dover transmitter is likely to vary greatly owing to the slope.
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Cherry White: Tay Bridge does not broadcast ITV4 or any of the Commercial channels, thus he is not receiving them from it. He is probably picking up from a different direction to which his aerial faces and is therefore "lucky" to get any signal.
Different receivers have differing sensitivities, so some may get and some may not when the signal level is borderline.
It "may" be the case that if he had an aerial directed to the transmitter which he is receiving it from that the signal level would be much improved and therefore would be available on all of his receivers. It would also reduce the likelihood of intermittent reception which could ensue because he is using his aerial to receive a signal which it was not installed for.
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Cherry White: As Mark says, an idea of your location may allow us to gauge as to how likely you might be to receive from a transmitter that carries all Freeview channels. Tay Bridge does not and will never carry all channels.
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Nick: I used Megalithia to plot the terrain between you and Dover:
Terrain between ( m a.g.l.) and (antenna m a.g.l.) - Optimising UK DTT Freeview and Radio aerial location
The curvature of the Earth would appear to be exagerated which is what I've experienced with Megalithia before over such long distances. What I did then was click the link below the plot to view the map between the two points.
I then found the co-ordinates for the point on the Kent coast where the signal path line intersects; this is at Birchington.
A plot from Dover to this point shows that there is clear line of sight:
Terrain between ( m a.g.l.) and (antenna m a.g.l.) - Optimising UK DTT Freeview and Radio aerial location
Unless there is any obstruction between your house and the coast, then this would appear to suggest that you do have line of sight to the top of the Dover mast.
The curvature of the Earth is said to be 8 inches per mile. This works out as 13.4 metres over the 66 miles.
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Stan: This is correct; Alexandra Palace only carries Public Service Broadcaster (PSB) multiplexes. It does not carry the Commercial (COM) ones which carry Russia Today, Al Jazeera, ITV3, Pick TV, Dave, Film 4 and others.
For a full list of Freeview services, see here (those with a bullet in the "E"/England column apply):
DMOL Post-DSO Multiplex Channel Allocations
There are three PSB multiplexes and three COM multiplexes. Each multiplex is carried as a single signal. PSB3 is the HD one.
Your current aerial may not be the best for Alexandra Palace, as it may be a Group A design (red tip). If it is a wideband, then it will be suitable. A wideband isn't needed for Ally Pally; a C/D aerial will work.
For information about aerial groups, see:
Aerials, TV Aerial and Digital Aerial
If you are considering realigning your aerial because you're having reception issues from Crystal Palace, then you may now be considering replacement of the aerial (still on Crystal Palace so as to get all channels). See this page for guidance and information about aerials for Crystal Palace:
Crystal Palace Transmitter
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Nick: The horizon is where the ground or sea "meets" the sky. There can be things on the horizon which are effectively "protruding" from the horizon.
Imagine if, after having gone over the horizon, the ship were to sprout a tall mast and fly a flag on it. The height of the flag may be visible over the horizon, even though the ship itself is not visible owing to the curvature of the earth.
The same appears to be true of the top of the Dover mast. Whilst it may not be possible to see it due the air not being clear, there is no land (hill) or other object inbetween it and you when on the top of your house.
It could be that the Kent coastline, and even the high ground on which the transmitter sits, is over the horizon (from your vantage point), but the top of the mast is not.
Visible light is also carried as electromagnetic waves. If you're driving your car at night you have the headlights on and they shine into the distance and on to objects which reflects the light back to you.
The more the mist and fog set in, the more difficult it is to see the objects. Headlights in dense fog result in illuminating the water droplets. The light becomes much more of a "ball" in front of you than a beam shining afar.
Conversely, other drivers see nothing of the radiated light until they are close. This is because the light is no longer travelling as far as it does when visibility is clear.
And so, I imagine that TV reception is much the same. The almost sudden loss of signal is probably down to a sudden mist moving in. The signal is travelling over the sea for over 40 miles.
Imagine what it would be like to look out from the top of the transmitter and see the signal being radiated. On a clear day, the signal will travel and objects a long way away will be visible in the "light" of the signal. When the mist comes in, the electromatnetic energy will end up getting "caught" in the droplets. What will be seen is the "light" reflecting back from the droplets. Those who can normally receive the signal will find that they get nothing or much less "light" than they normally do.
This suggests that you may not have stable reception of the COMs from Dover after all. You may have to listen to the Shipping Forecast to find out whether your viewing may be affected.
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Wednesday 4 July 2012 10:48AM
Jackie K: It could be the communal aerial system that needs adjustment.
They are sometimes filtered so as to only "let through" (from the aerial) frequencies used by the desired transmitter.
There are six frequencies (each known as a multiplex) for Freeview which each carry a number of services and those you mention are on the same multiplex (and therefore same frequency). This multiplex uses a frequency which wasn't used by Bluebell Hill before switchover. The other five use frequencies that were used before switchover (either for analogue or digital).
So maybe the aerial system needs adjusting for this new frequency.