Northern Ireland "mini multiplex" (NIMM)
Brian Butterworth published on UK Free TV A special service for 80%-90% of households in Northern Ireland will see three Freeview additional channels being available. These will be:
- TG4 - Irish language television channel - Teilifis Gaeilge
- RTE Television: RTE One
- RTE Television: RTE Two (in HD on Saorview)
Some homes will be able to receive the services directly from the Saorview transmitters in the RoI (see SAORVIEW - Ireland's free digital television service ), and others will, from the digital switchover date of Wednesday 24th October 2012, have a service provided from three Freeview transmitters in Northern Ireland.
- Brougher Mountain at 2kW on C30 (
speculativlyC30) - Black Mountain at 1kW on C39+
(speculativly C48) - Carnmoney Hill 16w on C48 (
speculativlyC48)
However, you will not be able to view these services using a standard-definition Freeview receiver - a Freeview HD box or set will be required. It is not known at this time if the NIMM will carry RTE2 in HD, as per the Saorview service. TG4 and RTE1 are broadcast in standard definition at the moment.
The requirement for a Freeview HD receiver is because the services are being broadcasting in "D-Book Option 11", which uses the DVB-T2 standard ("a new mode, option 11, is being planned for a multiplex in Northern Ireland. Receivers should be able to switch between these automatically", D-Book 7, DTG164 is defined in appendix G as: FFT size 32k, 16QAM modulation, 1/128 guard interval, PP7, FEC 64800). Digital Television - Technical guidance on the availability of TG4 in Northern Ireland after digital switchover says that Option 11 is: DVB-T2 16QAM FEC 1/2.
Update: DVB-T2 16QAM FEC 1/2 provides a bitrate for the multiplex of 12.77Mb/s.
Update: DVB-T2, QPSK modulation, FEC 2/3, 32K carriers, 9.954 Mbit/s.
Help with Freeview, aerials?
In this section
Monday, 20 February 2012
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Mike Dimmick2:51 PM
PaulN: The new Divis mast's main antennas are not suitable as the coverage required is directional: 2kW in one direction, 1kW in another. Divis' antennas are omnidirectional, equal power in all directins. There isn't sufficient space on the new mast for the additional antenna required. I assume that the full requirements for the NIMM weren't worked out before the plans for the new Divis mast were submitted, or it would be too tall for Belfast Airport's flight path if the NIMM antenna were on there as well.
There *is* space, or will be, on the Black Mountain mast. Black Mountain was deliberately sited very close to Divis by the Independent Television Authority in the 1950s, so that viewers' aerials would point in the same direction for both BBC and ITA (i.e. UTV) signals, and a combo aerial for VHF Band I and III would be possible. VHF signals were shut down in the mid 1980s, but from 1997 Channel 5 used this to their advantage, sending out 50 kW from the top of the mast, rather than having to settle for a poor location much further down the Divis mast.
The confusion arises because Black Mountain is also a low-power UHF relay for BBC One, BBC Two, UTV and Channel 4 analogue. The transmitting aerials for this are way down the mast, they are only intended to cover a small area which is otherwise shadowed from Divis itself.
For the standard PSB mode, 64QAM 2/3, about one-fifth of the power of analogue was believed to be required to give the same coverage. Some sources say one-tenth, and the experience seems to be that one-fifth gives a larger coverage area than analogue. For this reason, the commercial multiplex operators have decided to start using a higher-capacity mode, 64QAM 3/4, which requires 1.5x-2x the power of the PSB mode to give equivalent coverage. The mode selected for the NIMM requires less than one-tenth the power of the PSBs, or 1% that of analogue, to deliver equivalent coverage.
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Peter Henderson2:56 PM
"I don't understand why NIMM doesn't have a place on Divis. What am I missing ?"
Originally Paul, it was to be housed on the old mast at Divis (Divis now has two masts) the new one being constructed for DSO and DAB radio. The old mast was to be retained for the NIMM and nalogue FM rdaio.
However, I've read elsewhere that the National trust has objected to the two masts being retained at the site. The old mast will now be deommissioned at some stage, so I assume this is why Black Mountain will be used instead (Divis was initially one of the proposed sites).
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PaulN3:37 PM
Larne
Ahh - some good info there... a couple more questions for clarification then.
1 - On the assumption that the RF mode of the NIMM needs 'one tenth of the power' - did I see it right that NIMM power from Black Mountain is touted at a paltry 1 or 2 kW - versus the shocking 100kW that I see forecast for DSO at Divis (I suspect that 100kW is a total for all the muxes - not each one or the sky would surely melt) ?
2 - Did I also not see that Black Mountain transmits with Vertical polarisation today versus the Horizontal from Divis - hence a 2nd aerial required - or is the NIMM planned to go out on Horizontal as well ?
Apologies if I am reading too much confusion into some of the headline numbers I have seen referenced on the site - this RF stuff is a mad black art but I have enough grasp of the fundamentals to still be confused. Lord knows how the average non-techie bloke or granny is going to get their head round some of the DSO issues.
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PaulN's: mapP's Freeview map terrainP's terrain plot wavesP's frequency data P's Freeview Detailed Coverage
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Peter Henderson4:54 PM
What Mike is suggesting Paul, is that 2 kw for the NIMM will be the equivelent of around 20kw of a standard Freeview signal, which means the 1/2 kw ERP is somewhat misleading.
The polarisation has yet to be mentioned, but I would imagine it should be horizontal as it's got nothing to do with the low powered relay.
Viewers in West Belfast that use the low powered relay will obviously need two aerials if this were the case.
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Wednesday, 22 February 2012
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PaulN1:17 PM
Thanks for the clarifications... It will be interesting to see if NIMM can be received in East Antrim with a single aerial pointed vaguely at Divis come DSO day.
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Peter Henderson3:55 PM
That's what I was wondering.
Which part of East Antrim are you located Paul ?
I'm in Jordanstown and currently have OK reception of FReeview from Divis, even though the Carnmoney Hill Transmitter is only a couple of miles away (I can see it from my bedroom window). Analogue reception of Clermont Cairn is also perfect, but nothing from Saorview (apart from placeholders that appear every so often). I fully expect Sarview reception to be perfect after 24th October 2012, hopefully.
I'm not so sure about the NIMM from Black Mountain though, but if what Mike and others say is true re. the technical paramaters etc. it should be OK. Failing that, I'll put something up for Carnmoney Hill if both Black Mountain and Clermont Cairn are rubbish.
The 24th October 2012 should be very interesting indeed and well worth waiting for.
If other DSOs are anything to go by, there's going to be quite a lot of problems with signal strengths being far too strong.
The Hannington transmitter analogue switch off is certainly interesting, judging by the comments.
I'm also getting reasonable reception from the Cambrett Hill transmitter in Southwest Scotland, including Freeview HD, which looks very good indeed.
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John Rourke4:07 PM
So can anyone answer a straight forward question Will Divis broadcast the RTE multiplex come October?
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Mike Dimmick4:44 PM
John Rourke: No, but Black Mountain will. Channel 5 analogue currently comes from Black Mountain, not Divis - the sites are about a mile apart.
If not, your equipment may still pick up transmissions from the Republic, depending on where you are.
At least, it will launch in October if RT have selected a preferred bidder in time - because RT are a state organization in Ireland, they must run a full competitive tendering process according to the EU's rules, they can't just hire Arqiva (the mast owner/operator) to do it. If someone else gets the contract, they then have to agree terms with Arqiva for access to the masts to get the aerials put up - though I think Arqiva have already started doing work speculatively.
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Friday, 24 February 2012
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PaulN12:04 AM
Larne
@Peter - I am Larne area. Much of Islandmagee seems to have patchy coverage for Freeview from Divis today due to the geography, and much of Whitehead sits in a dip that will see most folk needing a dish for DSO.
I have never bothered to check if my house aerial is the correct type - the previous owner was a complete dullard / cheapskate so will have certainly applied no braincells to the solution. But I digress. Sometimes bad weather causes some channels to be heavily errored - usually on the BBC1/2 mux for some odd reason... must be the most sensitive / borderline to my hokey S/N ratio on the outer limits of Divis footprint.
Are you suggesting that SaorView signals will be receivable across NI cos I didn't think that was the plan - although its fair to expect some overspill near the border which folk might need a 2nd aerial to pick up.
I will perhaps investigate the Scottish option as well, though clearly I was looking in the wrong parts of this site to try and find the nearest Freeview mast across the water that will stay active for DSO.
I probably need to find a friendly neighbourhood aerial man to help with some tests as I don't fancy hanging off the roof waggling an aerial with a signal strength meter in the other hand.
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PaulN's: mapP's Freeview map terrainP's terrain plot wavesP's frequency data P's Freeview Detailed Coverage
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PaulN12:18 AM
Larne
So then... the plot thickens - in theory at least.
According to the SaorView site - parts of East Antrim should indeed be able to receive the signal from Clarmont Cairn.
As for the works required by RTE at Black Mountain for activation of the NIMM - is that to be done by professional DVB-T2 receivers/turnaround for the signal from Clarmont Cairn and then retransmitting the RTE channels into the NIMM or is there something more complicated ?
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PaulN's: mapP's Freeview map terrainP's terrain plot wavesP's frequency data P's Freeview Detailed Coverage
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