All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Lynda: The Wales and West regions have completed switchover - there aren't any major changes to come for the public service channels. The commercial multiplexes at Wenvoe are changing frequencies on the 27th, and many get an increase in power, but this won't affect any regional news services.
You could try deleting all the channels and adding them manually. However, it really sounds like you have a horizontally-polarized aerial pointing at Wenvoe and the levels received from Backwell just aren't high enough for the TV to receive reliably.
You could try removing the aerial connection, performing a complete reset of the TV ('Reinstall All Services'), wait for it to retune (it shouldn't find anything), then plug the aerial in and enter the frequencies manually. For the Public Service channels use the frequencies I gave above. For the commercial channels:
Now: C51/714MHz C30/546MHz C49/698MHz
27 April: C42/624MHz C45/666MHz C49/698MHz
You may get two copies of E4, because in Wales, the slot on D3+4 is taken by S4C and E4 is broadcast on the SDN multiplex instead.
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Graham: There's no such thing as analogue or digital cable. It's all just 75-ohm coaxial cable.
However, for analogue terrestrial TV in the UHF band, it was normal to use a fairly cheap cable frequently called 'low loss coax'. It probably was 'low loss' compared to the stuff used for 405-line VHF TV, but it's not really that great. The major problem is that the screen - metal strands just beneath the outer insulation - is very sparse. This allows it to pick up a lot of electrical noise.
On analogue TV, a brief bit of electrical noise just causes a bright or dark patch usually just on one line - blink and you missed it. For digital, it usually causes the picture to break up for a frame or two and the sound to cut out or glitch.
It's now recommended to use 'satellite-grade' cable, with a dense braid over copper foil tape screening. This is much less likely to allow interference, and much less signal is dropped over the same length.
If you don't notice any noise on the picture of any of the TVs now, you probably don't need to do anything. Get someone to watch the sets while you turn your thermostat on and off, run the vacuum cleaner, start and stop the cooker (if electric), and just see whether there's any visible noise or patterning.
You should already be able to get reliable digital pictures, if your aerial points to the Waltham or Belmont transmitter. Waltham is most likely. It could also point to the Sutton Coldfield transmitter, but you probably won't get a usable digital signal from there yet (and it's not your best option). If you get BBC East Midlands news, it's probably Waltham. If West Midlands, Sutton Coldfield. If Yorkshire & Lincolnshire (Look North), Belmont.
Switchover dates: Waltham, 17 August; Sutton Coldfield, 7 September; Belmont, 3 August.
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Arthur: Yes, you need to have a viewing fest. Sky disable the recording, timeshift and playback functions unless you keep paying for a basic subscription.
You can feed as many boxes as you like from one satellite dish, as long as they're using independent outputs on the LNB. You can't split cables, because the box sends signals back up the cable to control the LNB. You need two cables from a recorder (Sky+ or Freesat+) to the dish so that it can select different modes for the channel being watched, and the channel being recorded (or for the two channels being recorded).
If there are no spare outputs on the LNB, it's possible to just buy a replacement LNB rather than a whole new dish.
The Humax FOXSAT-HDR does have an 'LNB 1 OUT' socket on it, which you could plug the Sky box into. However, if the Humax is on, or recording two channels, you would only be able to watch some of the channels on the Sky box - those which have the same mode. It's really recommended to connect directly to the LNB.
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Lee: The relays are only there to fill in gaps in reception. You ought to get best results from the main station at Wenvoe. There's a hill (western end of Garth Hill) between you and it, but the transmitter is so strong that even the much-reduced signal should still be strong enough.
The Mynydd Machen relay is only designed to serve the valley to its north, and possibly part of Machen itself. The map here is hopelessly wrong because Brian hasn't integrated the actual radiation pattern of the transmitter, and his terrain data is too imprecise.
The Pontypridd relay to your north looks to be blocked by the hill just to your north at Coed y Fardre. At only 400W there likely isn't enough signal getting through.
There is also a relay at Taffs Well to your south-east, only 10W but no obstructions (there's a hill, Maesbach, but you can see over it). That's your best option if Wenvoe and Mendip aren't possible.
For best results from Wenvoe you should have a Group B aerial, horizontally-polarized (rods going side-to-side), pointing slightly east of south. For Mendip, a Group C/D horizontally-polarized pointing slightly north of south-east. For Taffs Well, Group C/D *vertically* polarized (rods going up-and-down) pointing slightly south of east.
A wideband will work reasonably well for group C/D transmitters, less well for group B.
The commercial multiplexes at Wenvoe are boosted on the 27th of April, and you'll need to retune because the frequencies are changing. However, if your problem is with BBC channels, ITV1, S4C, Channel 4 or Channel 5, or with HD services, nothing will improve because nothing is changing - these are in their final channels and modes and at final power levels at all of the transmitters you could use.
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M.Rothwell: Mendip broadcasts the West region services, which for BBC news is Points West. You could also be using Stockland Hill (BBC Spotlight south-west news) or Wenvoe (BBC Wales). ITV1 broadcasts 'The West Country Tonight' from both Mendip and Stockland Hill, so it's harder to tell.
Given that you have similar signal levels from a Group A transmitter (Stockland Hill), a Group C/D transmitter (Mendip), and a Group B transmitter (Wenvoe), I'd strongly recommend a grouped aerial. You're much less likely to get a 'region overlap' problem, where the box selects services from the wrong region that you then have problems with, because the signals received off to the side are poor.
As the signals from all transmitters are pretty strong, I'd go for an 18-element Yagi. In the loft you might want to try an aerial with X-type elements because these are shorter than the equivalent Yagi for the same performance - outside the Yagis are usually recommended because they have less surface area and are blown about less by the wind.
There's a reasonable chance your aerial is already suitable, but you have an overlap problem. See if your box or TV has a status information or signal strength menu which lists the frequencies used, and look at which way the aerial points. It's most likely that your aerial points north-east to Mendip, but could have stored channels from Stockland Hill.
Mendip: C61 C54 C62 C56 C67 C58
Stockland Hill: C26 C23 C25 C22 C28 C29
Wenvoe: C41 C44 C51 C30 C49 C47
To check all the frequencies, go to BBC Two, then ITV1, then ITV3, then Dave, then Yesterday. The final frequency in each list is for HD services, so if you have HD equipment, try any HD channel. (I said BBC Two above because there is now BBC One and BBC One HD, but any BBC service will do.)
If you find that it is storing signals from the wrong transmitter, you have a few options. You could try adding an attenuator when retuning, which hopefully will reduce the levels of the signals you don't want enough that the box won't see them. You might be able to leave it connected all the time if signals are strong enough. Or you might have to fit a filter (or use a diplexer as a filter) to reduce the level from the unwanted transmitters still further. Using an aerial of the right group should help. The cheapest, but most annoying, ways are to unplug the aerial when retuning and only plug in once it's got past the unwanted transmitters (but there's not much gap between Wenvoe at C49 and Mendip at C54), or to retune manually.
Newer Freeview HD boxes and TVs should store the strongest signal rather than the first encountered. Some of them also ask which region you want to store, if it finds more than one.
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Sam: It's likely that you now have too much signal. If you have a booster or amplifier, try removing it. If that doesn't help, try adding an attenuator.
You might temporarily lose some channels on other multiplexes, so if you have a booster and there's a gain control on it, you could try turning it down rather than removing it completely, or you might try a variable attenuator rather than a fixed amount. The commercial multiplexes won't all reach full power until around April 2012, and extra interference could cause you problems once another transmitter switches after that.
Digital UK predict that you should get a better service (or at least a better probability of getting a reliable service) from the Tacolneston transmitter, once that switches in November. It's a little further away and will be about half the power of Sandy Heath, but there should be less interference.
The BBC have had to increase the compression a bit as, while the new multiplex has more capacity than the old one, they also have to fit some channels in that used to be on Mux B (BBC Four/CBeebies, BBC Parliament and an interactive stream). You might notice some artifacts. It's still less than on the ITV multiplexes, though.
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Scott: if you get occasional breakup or loss of channels, 10 dB is a great improvement. If everything's solid now, you won't notice a thing. If you already have very high percentages, you could run into problems with too much signal.
The Humax HD boxes are supposed to be properly calibrated this time (the SD boxes aren't), so 95% is safe for now - but it indicates a pretty large signal. Adding 10dB is likely to be too much signal. If you get picture break-up or loss of channels after the switchover, remove any amplifiers or boosters, and if that doesn't fix it, try adding an attenuator.
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David Pearce: I used the postcode NR28 9JS with Digital UK's postcode checker, trade view. It shows that BBC A, D3+4, and the HD multiplex are expected to get worse in 2012.
The commercial multiplexes at the Dover transmitter will be using these frequencies (C55, C59 and C62). I think this is why the prediction deteriorates - they are north of Tacolneston so the aerial will point in roughly that direction. Yes, Dover is a long way away and signals are blocked by the curvature of the Earth, but in the right (or wrong) weather conditions, signals bounce off the atmosphere and travel further than you'd think. They might experience break-up at night.
It may be possible to reduce the problem by rotating the aerial several degrees clockwise, so it points a bit to the right of Tacolneston, and doesn't pick up as much from Dover.
The Midhurst transmitter will also transmit on C55 but this is even further away and much less powerful. DUK show little impact from this.
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David Brient: if there's a time of day that you've noticed that ITV, C4 and C5 were normally working, try retuning it then. Or try a manual update of channels on C45.
You are predicted to have variable reception of these channels at the moment. No problems are shown once switchover completes on the 13th (10 days time).
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Sunday 3 April 2011 5:57PM
Reading
Kenneth Muir: I'm afraid Kenmore is a 'Freeview Lite' transmitter, which only transmits the three public service multiplexes. The commercial multiplex operators were offered the opportunity to broadcast from additional sites after switchover - they turned it down. They claim it is too expensive.