Another BBC DAB - NI

lawhec wrote: »

Same site as the MW TX site I take it?

Spot on - Up the side of Erne Integrated School.

The Cush wrote: »

Previous posts indicated Tully Hill, Sligo and Clermont Carn.

So it's Belfast Tully Hill not Sligo and no mention of Clermont Carn in that list. No NI DAB sites south of the border.

No it's Tully Hill (The Downtown Radio site in Portglenone) that's what the NGR is refering to. Still digesting this list but Carnmoney Hill not on the list?

On the original list did no one twig that isn't Clermont Carn's NGR??

Peter Henderson wrote: »

Apparently Carnmoney hill is next after Bangor Sam.

Jordy also tells me the 10C and 11D sites are allocated for a future Digital One expansion into the province though no timescale is given.

Looks interesting for DAB here in a few year's time then, hopefully.

This list has me absolutely perplexed to be honest - I have gone through every Arqiva planning document i have and none of this adds up.

The BBC multiplex on block 12B is part of a UK-wide single frequency network, so could in principle cover the whole of Northern Ireland, subject to restrictions towards the Republic of Ireland to protect their upper adjacent channel allocations on blocks 12A and 12C. The Northern Ireland local multiplex is more constrained as it shares block 12D with local multiplexes in other parts of the UK. Some of these multiplexes are in service (for example Stoke) while others are planned but not yet implemented (for example Carlisle, Morecambe Bay and Colwyn Bay).

Arqiva found that there would be benefits to DAB coverage in Northern Ireland if the as yet unimplemented multiplexes at Carlisle, Morecambe Bay and Colwyn Bay could be assigned alternative frequencies from the new five blocks (10A to 11A). This would allow the Northern Ireland multiplex to broadcast more power to the east. However, there still remains a major restriction in the direction of the multiplex at Stoke which is already on-air, and this too would need to be assigned a new frequency.

As the multiplexes in Northern Ireland and the Republic are upper adjacent, there are particular limits on the levels of services from each territory are permitted to develop at the border. The multiplexes in Northern Ireland are already broadcasting at the maximum level permitted by the UK’s agreement with the Republic of Ireland. Any power increases for the multiplexes would therefore require clearance with the Irish Administration.

Arqiva's own words - By allocating frequencies from the ‘new’ five blocks to the proposed and unimplemented multiplexes a small improvement could be made to the coverage achieved by the Northern Ireland local multiplex. For maximum benefit, the frequency used by the multiplex at Stoke would also need to be changed. However, for the power levels of either of the two Northern Ireland multiplexes to be significantly increased such as to would be required to account for indoor coverage would require international re-negotiation.

Particularly harmful to us - It is technically possible for Digital One to use block 11D in Scotland. The present situation is that in England & Wales the service uses block 11D whereas in Scotland it uses block 12A. Having the same block in all areas would give network planning advantages in the border area. It would also allow the provision of a Scottish national network on the vacated 12A frequency block. However, such a change would stop any Scottish opt-out for the existing Digital One service.

This then causes a 'catch 22' situation were the 11D block could not be used in Northern Ireland due to interference problems Except in cases were expansion of the local multiplex is required at any significant power. The wording is key there 'Expansion of the local multiplex' and notice all the sites are to the west were interference with the mainland is limited.

Very skeptical indeed...

Peter Henderson wrote: »

Is there a big interference problem with the multiplexes in NI and the mainland and NI Sam ?

I live in an area that has good FM reception between here and Northwest England/Southwest Scotland and I very, very, rarely hear anything at all from across the water when it comes to DAB, exept under extreme lift conditions and that's with an external folded dipole on the chimney (up about 30ft) . To be honest, I can't see an expansion of Digital One into the province once the ROI's VHF TV frequencies have been cleared, causing much of a problem.

Jordy did say the time scales were uncertain so we'll just have to wait and see. So far, all his predictions do seem to be correct so I'd be opomistic Bangor, Carnmoney Hill, and Newtownards will be next.

Driving along the O'Neil road today, I thought I noticed something new at the top of the tower.

There will be a huge interference problem if what is being proposed on that list. Arqiva themselves spell out if on the assumption that no new tx's are built and restriction to the coastal sites on the east are removed. The local multiplex can enjoy a mere coverage increase of 3% of population. Also states band 3 frequencies in other countries (Ireland) will not be used indefinitely and the French Military still occupy band 3 frequencies that share blocks with Northern Ireland and Carlisle.

I would like to know two things were this list came from and who created it? Unless your source on UKFREETV is involved or is in contact with someone on Arqiva's Spectrum planning team then this list isn't real. Just to say i flagged it up via e-mail to a number of well respected trade experts and industry folks who have more of less fobbed it off.

Mike 1972 wrote: »

Excuse me for asking a potentially n00b question.

Why are there issues surrounding "upper adjacent" and "lower adjacent" multiplex frequencies. I always thought the Eureka 147 spec mandated "guard bands" in order to prevent such issues occuring ???

Because for example, the DAB channel allocated to the BBC for its nationals is centered on 225·64 MHz. The nominal width of the channel is 1·75MHz. However since the system uses COFDM, the symbol duration of 1 ms means that the 1536 DAB carriers are spaced 1 kHz apart. Hence the actual carriers for this multiplex spread over 1·536 MHz. This leaves around 100 kHz either side for the modulation sidebands, and to make it easier for RF/IF filters in a receiver to accept a wanted transmission whilst rejecting others in adjacent channels.

The UK DAB guard interval of 246us means that delayed versions of the transmission can arrive via paths which differ by up to the distance EM waves travel in this time. In practice, the DAB transmissions don’t bother to actually switch off the transmitted power during every guard interval. Instead the symbol’s amplitude and phase is used during the preceding guard interval.

Mike 1972 wrote: »

I was referring to guard bands as distinct from guard intervals

isint there (carriers and sidebands notwithstanding) a small amount of frequency space between adjacent multiplexes ?

Roughly 2mhz (0.176) i stated the channel spacing above.