Help with TV/radio stations?
In this section
Wednesday, 2 February 2011
M
michael9:32 AM
Quality, integrity : Moving the telescopic aerial on my DAB receiver just slightly affects signal strength and/or quality rather drastically. It is far more temperamental than FM at half the frequency. I would be interested in signal quality maps to compare theory with practice. The coverage maps I have seen are basically predicted field-strength maps, so if better maps are available, I would be most interested in any links. Accidented topography is likewise even less DAB-friendly than it is FM-friendly, all the more so on the move. I cannot see DRM+ implemented anytime soon, but the extensive research and trials do indicate it is considered a serious future contender.
| link to this comment |
michael: Yes, but again, it's a digital transmission system, so the whole of the digital multiplex can be perfectly decoded right to the edge of the area.
DAB also works, as you already know, for mobile reception at any legal speed.
| link to this comment |
S
steve6:50 PM
How fast to stop it working? IIRC the radio waves do 3100 miles a second!
| link to this comment |
steve: It's the Doppler Effect - it changes the effective frequency of the signal if you move towards or away from the transmitter at great speed.
The COFDM system used by DAB consists of 1000+ sub-carries - at extreme speed these become distorted and unrecoverable.
| link to this comment |
N
Nedbod7:45 PM
If coverage doesn't match prediction I don't think I'll be on my own !!
| link to this comment |
Nedbod: That is very unfair. The current prediction models are highly accurate.
| link to this comment |
Thursday, 3 February 2011
M
michael9:27 AM
It is empirical and reproducible that moving the telescopic aerial of an FM or DAB radio can result in degradation of the signal quality. The general coverage prediction implies that there is a locally receivable signal, but factors immediate to the receive aerial, topography, buildings and obstructions being passed, house
attentuation, reflections etc, determine whether at a given dx/dt moment the signal is of sufficient quality to be demodulated or decoded. This is more significant at the higher frequencies of DAB. Ergo : unless the field strength is substantial enough to override immediate physical factors, reception quality of DAB and, to a lesser degree of FM, will be variable. Brian, you referred to reception quality maps, could you post links, please. Such would presumably include local topography and structure factors and be more detailed than the large-scale coverage maps.
| link to this comment |
Friday, 4 February 2011
N
Nedbod11:20 AM
That's precisely my point Brian future DAB prediction is subject to the way DAB reception behaves, particularly on the move in a car, due to surrounding topography and obstructions + indoors in walled buildings. This, in my opinion, is why DAB radios are not fitted as standard in many new cars. If we are not careful we will be switching off an FM/LW/AM system "before" we have proved whether or not its replacement does work in all the so called "predicted areas" and there most certainly will be more gaps in remote parts of the country as the new transmitters will definitely not be enough to duplicate LW coverage, which gets into just about every nook and cranny of Britain, parts of Ireland and quite a bit of Western Europe, even Jordan on occasions as I heard myself on a number of occasions when the atmosphere was suitable !! I don't expect DAB will manage that, not by a long chalk !!
This is similar to switching off analogue UHF only to find, in good reception areas, BBC1, 2 ITV1 & Channel 4 STANDARD Freeview is beaming out a poorer quality picture (even @ 100% signal strength) as a result of insufficient bit rate capacity. No mention of this in all the pre-switchover hype. All this plus the loss of Ceefax and the lack of ability to watch one programme whilst recording another, without splashing out on more expensive kit. You talk about choice but when you weigh up must of the output where is the real choice amongst all the repeats, which far fewer Freeview channels could easily accommodate. I'd love to see the viewing figures for some of these digital channels, but they seem to frightened to publish them. There was a time when the main four channels figures were on Ceefax but that ended years ago, funnily enough just as digital TV began ? It is also sad to see ITV restricting the higher quality HD versions of most of their channels to SKY & VIRGIN only. You would have thought that as ITV have ploughed quite a bit of dosh into FREESAT, all their channels would be available on that platform at least, ditto FIVE HD.
| link to this comment |
Monday, 7 February 2011
J
Jordy2:19 PM
Some interesting developments on the Digital Radio front - Launching on a four month technical trial from Craigkelly.
DRM+ Trial in the UK
For the first time, the technical capability of the DRM+ digital radio system in FM band II is going to be tested in the UK. This four month long trial, organised by the DRM Consortium and its partners, will take place in the Edinburgh area of Scotland from February 2011.
The DRM+ transmission will operate into an existing antenna that is shared with two FM services via a combiner. Those services cover more than 500,000 people in urban, suburban and rural terrain. This will be a closed technical trial with no direct involvement from the public.
DRM provides many features to allow user-friendly, high quality radio to be broadcast, including use of station names rather than frequencies, consistent digital audio, additional text and visualisation, an EPG, alternate service signalling, and automatic service following to DRM, DAB,
FM and AM services. More details can be found at www.drm.org.
The purpose of the trial is to measure the coverage of DRM+ operating in various transmission modes (lower capacity, higher ruggedness; higher capacity, lower ruggedness). There will also be a comparison of the coverage of FM and DRM+ in terms of transmitter power. Other objectives include being able to assess the impact of DRM+ on FM and vice-versa; demonstrate the performance of DRM+ in a range of environments, for example, urban, suburban, rural, etc., and therefore provide an analysis of performance against the challenges of these environments. The pattern of the antenna will also be measured, in order to correlate performance in different directions with the expected performance. This trial should also provide
suitable measurement data to international regulatory bodies, such as CEPT and ITU.
The trial transmissions will carry audio material consisting of both programme and test sequences. At least two modes will be tested to allow planning parameters to be determined for different scenarios.
I'am looking forward to seeing the results of this technical trial and the ability to use existing aperture is a development.
| link to this comment |
Select more comments
Your comment please