Much stronger DAB signal...

[Nick Armstrong]

I imagine it's since the switch to full digital in my area, but over the last month or so, I have noticed a huge improvement in the strength of the DAB signal at home. Due to the configuration of where I live, large parts of the place got no DAB signal before, with the best signal being fortuitously by the bed, ideal for the bedside radio. But even that was variable before, it seemed to depend on the weather (is that possible? How is DAB transmitted? can it possibly vary with atmospheric pressure?!.... I'd love someone to explain!)... sometimes dropping to only 2 or 3 bars, coming and going, and producing those horrible burbling sounds

But of late - the full 6 bars all the time... AND for the first time, the other DAB machine in the kitchen is picking up a signal - quite a strong one (before, it could only be used to play SD card recordings of TTN etc).

Anyone else noticed the same? And can anyone confirm that the change is to do with "going digital" - I presume it must be.

In which case: hurrah!

[Serial_Apologist]

You could be right in detecting improvement, Caliban. At least, there's no interference on 3 today. In any case the reception here always seems better during the day than evenings, which is when I do most of my listening!

[Gordon]

I imagine it's since the switch to full digital in my area, but over the last month or so, I have noticed a huge improvement in the strength of the DAB signal at home. Due to the configuration of where I live, large parts of the place got no DAB signal before, with the best signal being fortuitously by the bed, ideal for the bedside radio. But even that was variable before, it seemed to depend on the weather (is that possible? How is DAB transmitted? can it possibly vary with atmospheric pressure?!.... I'd love someone to explain!)... sometimes dropping to only 2 or 3 bars, coming and going, and producing those horrible burbling sounds

But of late - the full 6 bars all the time... AND for the first time, the other DAB machine in the kitchen is picking up a signal - quite a strong one (before, it could only be used to play SD card recordings of TTN etc).

Anyone else noticed the same? And can anyone confirm that the change is to do with "going digital" - I presume it must be.

In which case: hurrah!

It depends where you live Cal as to whether you get a substantial improvement in signal strength but many areas of the UK have. Some areas have been boosted significantly - the latest of note is London with a new transmitter - after the BBC has been adding transmitters at the rate of about 3 a week during 2011 and continuing now at a slower rate. The commercial sector [ie CFM] has not been so active of course due to lack of funding and incentive.

Anyway the nature of coverage and field strength is a complex subject but here's the top line:

• Radio transmissions of all kinds [not only DAB, also FM] are subject to the weather and atmospheric conditions generally. That is why your bars on the signal strength indicator bobble around and this is especially so when the input strength is low as it clearly was in your case [prior to improvement]. That is due in part to the way that the indicator works - at high strength the indicator is less likely to bobble so much. It varies from receiver to receiver design. Normally some of this bobbling will be caused by interference from other stations but because of the way in which DAB works this is not such a major problem as it can be with FM and with TV.

• One expects the radio waves to travel directly without obstruction to receivers but generally they don't especially if there is no external antenna high up so receivers indoors and low down suffer from the loss of signal which can be very substantial. FM is planned on the basis of an external high up antenna.

• RF transmissions also suffer when there is hilly terrain and also if they are heavily wooded, in summer especally when the leaves are out in full, or in urban areas with high rise buildings. At the wavelengths used by DAB [aound 1.4 metres] any object about that size will cause the wave to be disturbed and deflected/refracted and this can cause pockets of low strength in its wake or conversely it can also concentrate the signal and increase the strength. This is all dynamic and varies as for point 1 above. Generally for an indoor receiver with its own whip antenna there is never a direct reception path and it has to rely on many reflections, each with its own bobbling factor, arriving at its location and adding constructively which they don't always do and sometimes cancel. Moving this receiver by only a small distance [comparable to the wavelength] can improve matters but not necessarily permanently as the signal path varies dynamically because of those many reflections. Going upstairs instead can usually offer a good improvement especially if there is a window facing the transmitter direction. To deal with these issues the planners have to add massive margins to the transmitters to increase powers to overcome these problems for portable receivers and this is what will happen for the planning of the proposed DAB switchover.

• Finally, the receiver will have an effect on quality because receivers are not all created equal. For example, consumers get no indication of the sensitivity of the receiver they buy. If they live in an area where there is plenty of signal then this isn't so much of an issue. However if you live on the margins [and with low numbers and powers of transmitters this is more likely] of the nominal coverage area [ie the area that a given service is rerquired to serve] then low signal is inevitable and so needs a more sensitive receiver.

• A shocking report was issued about a year ago by OfCom as part of their proposed DAB switchover coverage plan. It published sensitivity measurements [among others] on a range of DAB receivers available on the market. The best receivers were consistent with OfCom planning rules but many were not and some, even with well known brands, were dire and incapable of meeting the OfCom rules. None of this is known to consumers who then get a bad experience of DAB if they happen to buy a receiver with poor sensitivity. How are they to know? The identities of the offending receivers were not published. Manufacturers rarely publish in their handbooks any such technical detail.

• Here's the link to that report:
  
  

  http://stakeholders.ofcom.org.uk/binaries/consultations/dab-coverage-planning/annexes/annex-j.pdf

  
  
  Look especially at figures 7 and 8. They show that the range of sensitivity is about 200 times [24 decibels] . That is, the worst receiver was 200 times less sensitive than the best. You may unwittingly have bought one of those bad receivers and blame DAB coverage for its apparently poor signal. One absolutely crucial aspect of receivers is the antenna; some of this dire performance is undoubtedly because of poor antenna design which is sometimes limited by aesthetic consderations.

• For switchover government is intending to require a test and a Tick Mark for compliant receivers [domestic and in cars] similar to the one used for TV sets and TV DSO so that consumers have some idea what is good and what is not. Needless to say some manufacturers are dead against this idea of testing sensitivity. One reason for this is that for the test to be meaningful it has to be complex and expensive and test the whole receiver, including its antenna as it would be used in practice by a consumer. Testing receivers in cars is next to impossible and so only the electronic part can be tested easily, not the antenna which is crucial.

This isn't an exhaustive list but gives some headlines. If you have any specific queries on the DAB switchover project or reception please ask.

[Globaltruth]

RF transmissions also suffer when there is hilly terrain and also if they are heavily wooded, in summer especally when the leaves are out in full, or in urban areas with high rise buildings

If you have any specific queries on the DAB switchover project or reception please ask.

What a kind offer.
The part of Derbyshire we live in has absolutely zero DAB coverage, and I have absolutely no idea how that may change, as according to DAB coverage websites there are no new transmitters planned.

Even when we do eventually get DAB coverage we live surrounded by hills which are heavily wooded on two sides.

Our way round this is internet radio and we also have a couple of FM transmitters - but I would be interested on your thoughts of what the future may hold in terms of DAB reception.

I have had DAB in the past at other places I've lived, and so have a couple of quite expensive DAB receivers stashed away uselessly...

[Gordon]

Thanks. To give a reasonable assessment of your future DAB prospects I’d need to know more accurately where you are eg nearest town say and the orientation of the area – eg if in a valley/dale which way does it align NSEW. I assume that you have been looking at postcode data etc for the current state of the network and that this will give you no comfort. Anyway it’s only a guide and cannot be totally relied upon. If you have poor or no DAB it’s possible that will have poor or patchy FM stereo too as the maps for Derbyshire indicate.

Meanwhile if your broadband is up to it [often limited in rural areas too] then that is a way forward as you have found. There is unlikely to be cable where you are so the only other route is via satellite which means Sky or Freesat and more expense.

This link gives the latest OfCom predictions of cover [if build out is to switchover plans yet to be fully costed]. This plan will not come along until the decision is made to turn off FM which might happen from around 2015 at the earliest. It’s a bit technical but the gist is available in the summary.

http://stakeholders.ofcom.org.uk/broadcasting/radio/coverage/dab-coverage/

There are maps in annexes [look at Annexe B for DAB. A for FM with which it will become equivalent after switchover] which are indicative of future cover. The areas for extra signal are listed with links to the maps but there are no obvious Derbyshire centres. The idea is to replicate the current FM coverage for the BBC services and some commercial ones.

Looking at Derbyshire in general there seems to be little broad cover. The main source is from the East at Nottingham which reaches to the Eastern slopes of the moorlands as far as Burton [easy ‘cos the Trent valley is flat!] and Derby and up some of those dales that align towards north Nottingham where the transmitter is. Matlock is poor but Chesterfield looks good. Elsewhere it’s very patchy and aligned with the dales and on the tops around Cromford probably non existent. Partly terrain partly population density. Also same goes for the West side of the moorlands because the Stoke transmitter doesn’t reach there – and is probably not intended to. Perhaps Manchester will reach a few of the northern parts of the county around Leek.

Cover for the BBC is on a national “universal” basis ie 95%+ of population as for FM but limited by cost. The commercial channels are planned on the basis of suitable “editorial” areas ie areas with common cultural or economic interests and then a technical plan is designed to deliver a suitable signal across that area subject of course to cost limits.

Derbyshire, as with some other counties, suffers from high ground and deep dales with low population densities which immediately limits both elements of the planning but with the BBC having to make their best efforts to reach to as many people as possible. The solutions are to install additional local repeater transmitters operating in concert with larger ones and DAB is good at this but it still costs and there are diminishing returns.

[Nick Armstrong]

London with a new transmitter

That'll be it !!

But thank you for such a detailed explanation and analysis Gordon

Much appreciated

[Gordon]

Much appreciated

I'm London on Saturday afternoon so I'll collect that pint then if that's OK!

[mercia]

good to know that calabash is now able to enjoy the breakfast show in the kitchen

buckaroo

[Nick Armstrong]

good to know that calabash is now able to enjoy the breakfast show in the kitchen

buckaroo

Buckaroo too, mercia!!!

[Nick Armstrong]

Renewed thanks to Gordon, for prompting me to do some investigation - I've found that four new DAB transmitters were commissioned in April 2012 to improve reception in Central London including one at the BT Telecoms Tower - the Olympic Games being cited as the prompting factor.

Apparently it was done with some ceremony: http://mediaweek.co.uk/news/1128486/...l-radio-boost/

Good to know that it's not just window dressing - the kitchen DAB radio celebrated by mercia above is functioning on full signal now - a month ago, nothing

Moreover, I was noticing this morning that the sound seemed particularly rich and clear - and I see that the bitrate would appear to be superior to every other DAB station, 192kbps, if this list is to be believed:

http://www.stevelarkins.freeuk.com/london-dab-radio.htm#Stations

I wonder if anyone knows if that has been boosted too recently? Or if the improvement in sound is solely as a result of the stronger signal.

Either way: I approve!

[Gordon]

........Moreover, I was noticing this morning that the sound seemed particularly rich and clear - and I see that the bitrate would appear to be superior to every other DAB station, 192kbps, if this list is to be believed:

http://www.stevelarkins.freeuk.com/london-dab-radio.htm#Stations

I wonder if anyone knows if that has been boosted too recently? Or if the improvement in sound is solely as a result of the stronger signal.

Either way: I approve!

No Cal, all they have done is added transmitters which will give your receiver a better chance of getting an error free signal most, if not all, of the time, but that doesn't really affect the basic audio quality, its always been 192 at best and 160 when its "joint stereo". It's aways been "better" [ie more bit rate] than the other BBC channels too. A few years ago the sound was being criticised but "new coding equipment" seemed to improve matters but perhaps not the satisfaction of the true audiophile for whom nothing but perfection [whatever that is] will do. Glad you are happy though

[Bryn]

It's aways been "better" [ie more bit rate] than the other BBC channels too.

Not entirely true. When I first got DAB (a Sony 777ES and a Psion Wavefinder), Radios 1, 2, 3 and 4 were all at 192kbps mp2. Then we got a Christmas present from the BBC, a few extra channels and a significant drop in data rate (audio quality) for Radios 1, 2 and 4 and for a short while even Radio 3 dropped to 128kbps to make room for extra sport coverage.

[Nick Armstrong]

No Cal, all they have done is added transmitters which will give your receiver a better chance of getting an error free signal most, if not all, of the time, but that doesn't really affect the basic audio quality, its always been 192 at best and 160 when its "joint stereo". It's aways been "better" [ie more bit rate] than the other BBC channels too. A few years ago the sound was being criticised but "new coding equipment" seemed to improve matters but perhaps not the satisfaction of the true audiophile for whom nothing but perfection [whatever that is] will do. Glad you are happy though

Thanks again Gordon (Oh damn... you were in town today weren't you?! I missed buying you that pint! Have a couple on me now )

Yes, for the purposes of the bedroom and the kitchen, the signal via my two Pure Evoke-3 sets is a lot more than acceptable (though I see that model has been discontinued, not sure why) because low-ish level listening is the rule.

Still rely on FM through a rooftop aerial for the main HiFi though

[Gordon]

Not entirely true.... for a short while even Radio 3 dropped to 128kbps to make room for extra sport coverage.

Bryn is absolutely right, I'd forgotten that period of 128. The message board kicked up a bit of fuss at the time but that seems to have gone very quiet now unless I've missed something.

The plan to switch off FM at some point in the future [https://www.culture.gov.uk/images/.....n_Plan_V3.doc] will require radios to have DAB+ installed which one might think would be a chance to improve sound quality. Trouble is that will not be mandatory, it is only a condition on getting a Digital Tick [like that used or TV DSO]. It will be long time before someone [BBC?] starts using DAB+, for one thing it needs extra capacity in the multiplexes to simulcast services for as long as there are significant numbers of old non DAB+ receivers in the market.

I'm not holding my breath on the improved quality with DAB+ anyway because all they will do is put more services in, not use the extra capacity to improve sound. Also some in the the industry fought hard against DAB+ being required so how many will actually do it [to get the Tick] is yet to be seen. The argument is that it makes no sense to put a technology in a box that has no transmissions to respond to and for which there are are no plans.

[Bryn]

I'm not holding my breath on the improved quality with DAB+ anyway because all they will do is put more services in, not use the extra capacity to improve sound. Also some in the the industry fought hard against DAB+ being required so how many will actually do it [to get the Tick] is yet to be seen. The argument is that it makes no sense to put a technology in a box that has no transmissions to respond to and for which there are are no plans.

I'm not holding my breath either. Even if the Beeb does implement a DAB+ offering there must surely be no chance whatever that they would broadcast at 320kbps AAC-LC (as they do for the iPlayer's HD Sound facility).

A few months ago I finally got sufficiently fed up with the car radio/cassette that I inherited in my father's old Fiat Punto. I chose a JVC KD-DB52 which is DAB+ ready and also plays aac files as long as they are 'wrapped' up as m4a via its USB socket. So far I have had pretty reliable results receiving DAB on it, except when passing Ashford Hospital on the A30. Going towards Bedfont it simply garbles for a few seconds. Going in the opposite direction (towards Staines) it not only garbles but repeats a few seconds. So much for the 'magic' of COFDM. eh?