The Ten Myths of DAB

[An_Inspector_Calls]

Calm down dear, can't you recognize hyperbole when you see it?

[Gordon]

Rubbish. Even wet brickwork can seriously attenuate an already marginal DAB signal enough for the boiling mud to start or for it to totally fail to resolve. I, for instance, need a rooftop dipole to get decent, reliable DAB reception here in RG12.

Why rubbish!! It's all dependent on where you live. You clearly live in an area that is relatively poorly served with DAB transmitters. Here we struggle with FM to get anything on a portable that isn't hissy so we don't use it - Oxford 45 miles away over the downs and Rowridge 55 miles away and no local relay. The HiFi has a good quality FM receiver attached but needs a 6 element Yagi on the roof to get enough signal to get low noise results and even then there is some audible hiss. No such problems with DAB, short piece of wire hanging out the back and noise free results!! OK, perhaps DAB is not for audiophiles but here where I live DAB wins hands down. Like AIC I am no DAB apologist it just works for me.

I have a Sony DAB in the study that doesn't need an aerial plugged in to get DAB but it is more reliable if there is an aerial on the weaker local stations that I rarely listen to - we're 7 miles from Hannington [BBC] which isn't one of the most powerful transmitters at 5kW. Some local transmissions come from elsewhere at much lower power and we fall between regions anyway.

It is true that wet brickwork will attenuate radio waves especially at the short end - TV UHF will be worse than VHF and digital modulaton systems being what they are the difference between good and bad is only a few dB. There is also a height loss from roof top level [where field prediction is focussed] to ground [where clutter prevents good pediction]. Penetration loss and height loss for VHF could easily add up to more than 10dB, more in the wet. OfCom documents use a figure of 13.6dB which is an aggregated mean. There will be a standard deviaton around this so it could be worse.

By the way DAB+ fails faster than ordinary DAB, no bubbling mud just cut out.

[Nick_G]

Interesting Gordon. At our first place here I had the Triax 5-element Yagi beaming at Rowridge and there was no hiss on the nationals using a Sony ST-SA3ES tuner. Is your tuner a Quad? I think you may have told me. At this location I have the aerial beaming east so I can hear London stations as well as more interesting signals when there's a lift on ;)

You could probably pick up a good tuner with switchable IF bandwidths for the same or less than a current DAB set via eBay.

I do know that DAB (Band 3) signals are affected by obstacles more than FM signals (Band 2) due to their shorter wavelength.

Regards,
Nick

[Gordon]

Interesting Gordon. At our first place here I had the Triax 5-element Yagi beaming at Rowridge and there was no hiss on the nationals using a Sony ST-SA3ES tuner. Is your tuner a Quad? I think you may have told me. At this location I have the aerial beaming east so I can hear London stations as well as more interesting signals when there's a lift on ;)

Yes it is a Quad and I know I could probably do better but the low hiss doesn't bother me.

You could probably pick up a good tuner with switchable IF bandwidths for the same or less than a current DAB set via eBay.

I know. But beware of reducing bandwidth with FM it may help to reduce RF noise but it also increases distortion. I don't have a problem; the point was that to get good audio S/N you need lots of RF, way above threshold. All you need with DAB is to get a few dB clear of the threshold and stay there.

[An_Inspector_Calls]

Exactly, and if you restrict the IF bandiwdth, the birdies will go, but so will your audio bandwidth and it'll sound awful. And so it goes: a better aerial, turn it in the right direction, get a better receiver: Quad, Sony, on and on. Just get DAB/Freeview, stick a screwdriver in the aerial socket and away you go! ( Bryn: the bit in bold is hyperbole.).

[Eine Alpensinfonie]

I notice the BBC is continuing its almost fruitless attempts to persuade people to buy DAB radios - on Radio 5, which is rather pointless, as AM listeners to that station will hardly need persuading, but digital listeners will not need to go out and buy a DAB receiver, as they already have one, or already have Freeview or Freesat, rendering it unnecessary.

[Bryn]

Exactly, and if you restrict the IF bandiwdth, the birdies will go, but so will your audio bandwidth and it'll sound awful. And so it goes: a better aerial, turn it in the right direction, get a better receiver: Quad, Sony, on and on. Just get DAB/Freeview, stick a screwdriver in the aerial socket and away you go! ( Bryn: the bit in bold is hyperbole.).

Of course it's hyperbole, and as such unnecessarily misleading for those who might be taken in by it and think that DAB is always less picky about having an aerial than FM is, hence the "Rubbish". I got a fine 70dB+ signal via a 5 element chimney mounted Yagi for FM (from Wrotham) until those damned wood pigeons and collared doves snapped the reflector. Now it's down to around 50dB but still serviceable, with little hiss. However, DAB (in 3 different rooms, each fed from a chimney mounted simple dipole via a 7dB amp) is just so convenient for 'live' listening. Anything 'important' is accessed via the iPlayer's 320kbps aac-lc offering, which I find more reliable via the 'Listen Again' facility.

[JFLL]

Of course it's hyperbole, and as such unnecessarily misleading for those who might be taken in by it and think that DAB is always less picky about having an aerial than FM is, hence the "Rubbish". I got a fine 70dB+ signal via a 5 element chimney mounted Yagi for FM (from Wrotham) until those damned wood pigeons and collared doves snapped the reflector. Now it's down to around 50dB but still serviceable, with little hiss. However, DAB (in 3 different rooms, each fed from a chimney mounted simple dipole via a 7dB amp) is just so convenient for 'live' listening. Anything 'important' is accessed via the iPlayer's 320kbps aac-lc offering, which I find more reliable via the 'Listen Again' facility.

Bryn, I’ve been trying to follow this rather technical discussion of aerials. You mention a ‘5 element chimney mounted Yagi’. The questions for an average listener like myself might be (1) how much would this cost in terms of materials and labour on a tall Victorian three-storey house, probably now (Elf & Safety) needing scaffolding to get at the chimney, (2) would it necessarily work, and (3) how much ‘better’ would it make FM reception for the average non-audiophile R3 listener, compared with an ordinary DAB radio with an inbuilt aerial?

[Bryn]

Bryn, I’ve been trying to follow this rather technical discussion of aerials. You mention a ‘5 element chimney mounted Yagi’. The questions for an average listener like myself might be (1) how much would this cost in terms of materials and labour on a tall Victorian three-storey house, probably now (Elf & Safety) needing scaffolding to get at the chimney, (2) would it necessarily work, and (3) how much ‘better’ would it make FM reception for the average non-audiophile R3 listener, compared with an ordinary DAB radio with an inbuilt aerial?

(1) I paid around £20 for my Yagi and about another £10 for the cable, but that was a good few years ago. I have no idea what an aerial installer would charge. I put mine up myself. Not sure I would be as happy to do so now. Access to my roof is more difficult since an extension was built over the garage, and I am a bit less nimble walking along a roof apex these days. I do recall that when I had a Sky mini-dish installed (free of charge) about 15 years ago, the installer quoted a surcharge of £50 if I he needed to go up onto the roof. I had him mount it on the back wall instead.

(2) Almost certainly as long as it was pointed in the right direction with no major geological obstructions between you and the transmitter. Mine is aimed at Wrotham, which I think is around 45 mile away.

(3) If you can get a reliable, boiling mud free DAB signal, then given the likelihood of FM being withdrawn to free up bandwidth for other uses before very long, I would not now pay out to have an FM Yagi installed. However, I would suggest that a simple external dipole aerial might well offer considerably more reliable DAB reception than using a 'built in' telescopic aerial. On many DAB radios, the telescopic aerial can be unscrewed to reveal a standard F type aerial socket for use with a cable feed from an external aerial.

[JFLL]

(1) I paid around £20 for my Yagi and about another £10 for the cable, but that was a good few years ago. I have no idea what an aerial installer would charge. I put mine up myself. Not sure I would be as happy to do so now. Access to my roof is more difficult since an extension was built over the garage, and I am a bit less nimble walking along a roof apex these days. I do recall that when I had a Sky mini-dish installed (free of charge) about 15 years ago, the installer quoted a surcharge of £50 if I he needed to go up onto the roof. I had him mount it on the back wall instead.

(2) Almost certainly as long as it was pointed in the right direction with no major geological obstructions between you and the transmitter. Mine is aimed at Wrotham, which I think is around 45 mile away.

(3) If you can get a reliable, boiling mud free DAB signal, then given the likelihood of FM being withdrawn to free up bandwidth for other uses before very long, I would not now pay out to have an FM Yagi installed. However, I would suggest that a simple external dipole aerial might well offer considerably more reliable DAB reception than using a 'built in' telescopic aerial. On many DAB radios, the telescopic aerial can be unscrewed to reveal a standard F type aerial socket for use with a cable feed from an external aerial.

Thanks Bryn, that’s very clear and helpful. It does seems then that, given that FM is due to be phased out and our DAB signal seems to be pretty good, it might not be worth installing an FM aerial if it would involve getting on the roof (the house is just too high for DIY roof-climbing!), unless of course we have to have scaffolding put up for some other reason such as re-pointing the chimneys or repairing the roof.

[Resurrection Man]

Just for the record, FM is NOT due to be phased out any time soon.

[Bryn]

Thanks Bryn, that’s very clear and helpful. It does seems then that, given that FM is due to be phased out and our DAB signal seems to be pretty good, it might not be worth installing an FM aerial if it would involve getting on the roof (the house is just too high for DIY roof-climbing!), unless of course we have to have scaffolding put up for some other reason such as re-pointing the chimneys or repairing the roof.

Re. the proposed timing of the pending switch-off of national FM channels, Which have some rounded comments to offer:

http://www.which.co.uk/technology/audio/guides/digital-radio-switchover-explained/when-will-radio-switchover-to-digital/

Note, the target date is only a couple of years away, but targets are very often missed.

[Resurrection Man]

Thanks for that link, Bryn.

[Eine Alpensinfonie]

I cannot see the switchover being consumer-led.
Unless the criterion is whether the Eton chums all have DAB radios.
The reality is that most radios being sold are FM/AM only.

[JFLL]

Re. the proposed timing of the pending switch-off of national FM channels, Which have some rounded comments to offer:

http://www.which.co.uk/technology/audio/guides/digital-radio-switchover-explained/when-will-radio-switchover-to-digital/

Note, the target date is only a couple of years away, but targets are very often missed.

That Which link is useful. I note it says:

“a decision on switchover can only be made once:

· 50% of all radio listening is to digital.
· National DAB coverage is comparable to FM, and local DAB reaches 90% of the population and all major roads.”

Does anyone know of a source giving a timetable for extending national DAB coverage (e.g. R3) in specific areas? My particular reason for asking is that we’re toying with the idea of moving to a rural area which we know doesn’t have DAB coverage at present.