All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Richard: It was probably telling you that one had 66 channels and the other 88 channels. There is no channel 88 for UHF TV broadcasting and channel 66 is being released.
What's probably happened is that some of the multiplexes have a slightly different transmitter ID tag than the others - usually the presence of one or more dots following the name. This seems to be something that the broadcasters use when they change the configuration of a multiplex, which they think is catered for by the specification (the Digital TV Group's D-Book) but not all receivers comply with it properly.
You should complain to Philips about this, particularly if there is no way to combine the two sets together.
154 services does sound like a lot, so it's possible there is more than one transmitter being picked up as well.
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j_cocker: You may have too much signal. Remove or turn down the booster. If you provide a full postcode we can see what the prediction is for you, and the likely signal levels.
If that doesn't help, I would suggest using the procedure 'Restore virgin mode' from page 31 of the manual https://ukfree.tv/retune/Philips_DTR1500-05.pdf
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Kevin: Make sure you use the Full Retune (Default Setting, First Time Installation, Full Reset, 'virgin mode') option, to clear out the channel list completely. Some boxes don't understand that channels can move to an entirely new frequency and will not save changes to channels that already appear in the list.
A common problem is that the new signal levels are high enough to cause distortion in amplifiers (including the one in the box's tuner). If you have an amplifier or booster, try removing it or turning it down; if you don't, or that doesn't help, try adding an attenuator.
I'm afraid I can't find a manual for this Grundig box, so can't confirm whether it does or does not support the 8K mode. It dates from 2003, so it's possible that it doesn't.
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Mrs C M Syne: You have to retune all your digital equipment. Make sure you use the Full Retune/Full Reset/Default Setting/First Time Installation option (it's called different things on different boxes), because otherwise it may simply ignore the channels that it already knew about.
If you've already done this, it may be a case of too much signal. If you have a booster, try without, or turn it down. Different equipment will have different thresholds before distorting, so the TV could be fine while the PVR has problems.
There is still another step of switchover at the Craigkelly mast and its relays, next Wednesday - you will need to retune again.
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Katherine: When the BBC ALBA TV station is on-air, most of the BBC radio stations have to go off-air. This was the only way they could cram BBC ALBA into the space.
The only radio stations that remain on-air on Freeview are the digital-only stations with the largest listening figures: 1 Xtra, 6 Music and 5 Live Sports. BBC Radio 2 remains available on FM and DAB.
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Obviously the above only applies to transmitters in Scotland, including the Selkirk transmitter and its relays in the East Borders region. It may also apply to the Scottish service from Caldbeck.
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Nick: SCART can carry video in (at least) two ways - either as composite signals, or as separate Red, Green and Blue signals. Separate RGB should give a better picture. Composite (also shown as CVBS) is basically the same as a demodulated, baseband, PAL TV signal, so the colour information is still carried on a modulated subcarrier. The extra modulation and demodulation adds noise, and phase shifts can be introduced which introduce colour errors.
The RGB signals were originally intended for subtitle decoder boxes, so some old CRT TVs do overlay the RGB signals from SCART on top of whatever analogue channel is being watched. Also, they may have only some SCART sockets that support RGB input, the others only supporting composite.
You might also find support for S-Video, where brightness (luma) is on one pin, called Y, and colour on another, called C.
Check your box's manual for what the options are and how to set them. My Humax PVR-9200T defaults to doing RGB on the SCART socket labelled 'TV' and CVBS on the socket labelled 'VCR'. It can be changed to do CVBS on TV and S-Video on VCR.
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Dale: I agree that for small sets or long-distance viewing, you can't tell the difference between SD and HD. However, for larger sets, if you can't tell the difference, you probably have it connected by SCART.
SCART cannot carry HD signals. You must either use component video - three phono plugs, one for brightness, one for the red difference and one for the blue difference - or a digital connection, to get actual HD display.
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Peter: I'm saying that everyone you know had systems with too much overall gain. It didn't cause a problem before as the distorted analogue signals don't cause as much damage to neighbouring transmissions as high-power digital signals do.
As for why it comes and goes, signal propogation changes over time. Sometimes it's weaker, sometimes stronger. Radio wave propogation is affected by weather and by dust in the atmosphere along the signal path, just as light is (light is just an extremely high frequency radio wave). Radio waves also reflect and refract off layers in the upper atmosphere as boundaries between colder and warmer regions form: the combination of the direct path and the reflected paths may either increase or decrease signal levels, depending on the length of the indirect paths and the wavelength of the transmission.
'Tropospheric enhancement', one reflection off the atmosphere, generally happens every night as the atmosphere cools. 'Tropospheric ducting', where signals bounce between two such layers and then exit, causes signals to travel much further, but requires rare weather conditions.
Digital UK's predictions take account of these effects, using a statistical model. It reports a 100% probability - which it is, for the PSB muxes - if the combined expected variation of both the signal from Sandy Heath, and everything else using the same frequencies, is expected to give more than 36dB of signal-to-noise ratio. The transmissions need 17.3dB of SNR to be decoded reliably, the planners added 5.7dB of fudge factor, and 12.8dB more than this is required to guarantee to cover the variation in propogation ('fading').
That's still about 7 dB less than was required for completely clear analogue reception, which required 43 dB of signal-to-noise ratio. However, when you get less signal-to-noise ratio than is required, you just got a slightly noisy picture on analogue. Digital carries redundant information used to correct the errors introduced by noise and interference, but once the signal-to-noise ratio gets too low, all of the redundancy is exhausted and the errors start to get through to the higher levels, causing sound and picture drop-outs, and eventually the inability to interpret the tables that describe the services on the multiplex.
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Wednesday 8 June 2011 7:50PM
Briantist, NottsUK: The BBC's blog about it at BBC - BBC Internet Blog: Gearing up to deliver Wimbledon 3D says that it will be on BBC HD on all platforms - Freesat, Sky*, Freeview and Virgin Media.
* of course Sky and Freesat actually use the same transmissions.