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Full Freeview on the Divis (Northern Ireland) transmitter

first published this on - UK Free TV
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The symbol shows the location of the Divis (Northern Ireland) transmitter which serves 440,000 homes. The bright green areas shown where the signal from this transmitter is strong, dark green areas are poorer signals. Those parts shown in yellow may have interference on the same frequency from other masts.

Are there any planned engineering works or unexpected transmitter faults on the Divis (Northern Ireland) mast?

Divis transmitter - Divis transmitter: Possible effect on TV reception week commencing 25/09/2023 Pixelation or flickering on some or all channels Digital tick

Choose from three options: ■ List by multiplex ■ List by channel number ■ List by channel name

Which Freeview channels does the Divis transmitter broadcast?

If you have any kind of Freeview fault, follow this Freeview reset procedure first.

Digital television services are broadcast on a multiplexes (or Mux) where many stations occupy a single broadcast frequency, as shown below.

 H max
C27 (522.0MHz)551mDTG-100,000W
Channel icons
1 BBC One (SD) Northern Ireland, 2 BBC Two Northern Ireland, 9 BBC Four, 23 BBC Three, 201 CBBC, 202 CBeebies, 231 BBC News, 232 BBC Parliament, 250 BBC Red Button, plus 13 others

 H max
C21+ (474.2MHz)551mDTG-100,000W
Channel icons
3 UTV (SD) (UTV), 4 Channel 4 (SD) NI ads, 5 Channel 5, 6 ITV 2, 10 ITV3, 13 E4, 14 Film4, 15 Channel 4 +1 NI ads, 18 More4, 26 ITV4, 28 ITVBe, 30 E4 +1, 35 UTV +1 (UTV),

 H max
C24 (498.0MHz)551mDTG-100,000W
Channel icons
46 5SELECT, 101 BBC One HD Northern Ireland, 102 BBC Two HD Northern Ireland, 103 UTV HD (UTV), 104 Channel 4 HD NI ads, 105 Channel 5 HD, 106 BBC Four HD, 109 BBC Three HD, 204 CBBC HD, 205 CBeebies HD, plus 1 others

 H -3dB
C23 (490.0MHz)551mDTG-850,000W
Channel icons
20 Drama, 21 5USA, 29 ITV2 +1, 32 5STAR, 33 5Action, 38 Channel 5 +1, 41 Legend, 42 Great! Movies Action, 57 Dave ja vu, 58 ITVBe +1, 59 ITV3 +1, 64 Blaze, 67 CBS Reality, 69 HorrorXtra, 78 TCC, 81 Blaze +1, 89 ITV4 +1, 91 WildEarth, 203 CITV, 208 Pop Player, 209 Ketchup TV, 210 Ketchup Too, 211 YAAAS!, plus 16 others

 H -3dB
C26 (514.0MHz)528mDTG-850,000W
Channel icons
 Smithsonian Channel, 11 Sky Arts, 17 Really, 19 Dave, 31 E4 Extra, 36 pick, 40 Quest Red, 43 Food Network, 47 Film4 +1, 48 Challenge, 49 4seven, 60 Drama +1, 70 Quest +1, 71 That's 60s, 74 Yesterday +1, 75 That's 70s, 233 Sky News, plus 9 others

 H -3dB
C30 (546.0MHz)528mDTG-850,000W
Channel icons
 Quest Red +1,  Classic Hits, 12 Quest, 25 W, 27 Yesterday, 34 GREAT! movies, 39 DMAX, 44 HGTV, 52 GREAT! romance, 73 HobbyMaker, 76 That's 80s, 82 Talking Pictures TV, 83 Together TV, 84 PBS America, 90 Together TV +1, 235 Al Jazeera Eng, plus 19 others

 H -13dB
C36 (594.0MHz)528mDTG-125,000W
Channel icons
from 29th September 2014: 7 NvTv,

 H -40dB
C48 (690.0MHz)551mDTG-10W
Channel icons
from 4th September 2019: 53 TG4, 54 RTÉ One, 55 RTÉ Two,

DTG-8 64QAM 8K 3/4 27.1Mb/s DVB-T MPEG2
DTG-12 QSPK 8K 3/4 8.0Mb/s DVB-T MPEG2
H/V: aerial position (horizontal or vertical)

Which BBC and ITV regional news can I watch from the Divis transmitter?

regional news image
BBC Newsline 0.6m homes 2.5%
from Belfast BT2 8HQ, 1,044km northeast (51°)
to BBC Northern Ireland region - 46 masts.
regional news image
UTV Live 0.6m homes 2.5%
from Belfast BT7 1EB, 1,044km northeast (51°)
to UTV region - 46 masts.

Are there any self-help relays?

Chapel FieldsTransposerCentral Belfast61 homes

How will the Divis (Northern Ireland) transmission frequencies change over time?

1950s-80s1984-971997-981998-20122012-134 Mar 2020

tv_off Being removed from Freeview (for 5G use) after November 2020 / June 2022 - more
Table shows multiplexes names see this article;
green background for transmission frequencies
Notes: + and - denote 166kHz offset; aerial group are shown as A B C/D E K W T
waves denotes analogue; digital switchover was 10 Oct 12 and 24 Oct 12.

How do the old analogue and currrent digital signal levels compare?

Analogue 1-4 500kW
BBCA, D3+4, BBCB(-7dB) 100kW
SDN, ARQA, ARQB(-10dB) 50kW
com8(-16dB) 12.7kW
com7(-16.1dB) 12.4kW
LBT(-20dB) 5kW
Mux 1*, Mux 2*, Mux A*, Mux B*(-23.4dB) 2.3kW
Mux C*(-24dB) 2kW
Mux D*(-24.9dB) 1.6kW
NIMM(-47dB) 10W

Which companies have run the Channel 3 services in the Divis transmitter area

Oct 1959-May 2006Ulster Television
May 2006-Dec 2014UTV plc
Feb 1983-Dec 1992TV-am•
Jan 1993-Sep 2010GMTV•
Sep 2010-Dec 2014ITV Daybreak•
• Breakfast ◊ Weekends ♦ Friday night and weekends † Weekdays only. Divis was not an original Channel 3 VHF 405-line mast: the historical information shown is the details of the company responsible for the transmitter when it began transmitting Channel 3.

Tuesday, 6 November 2012
Mike Dimmick

2:48 PM

John Durrell: The difference in what your TV reports is *probably* down to using an external receiver rather than having the HD tuner built in to the set.

This is complicated by the fact that, on Freeview HD, the encoding hardware, and therefore the transmissions, can dynamically switch between 1080i50 and 1080p25 modes for every Group of Pictures (GoP). A GoP is a sequence of 15-25 pictures that are encoded using differences between the pictures, only one whole picture being sent in the set. The encoder switches mode based on how well the content compresses in each mode - if the source material was actually captured in progressive mode, or if there isn't much motion, it should compress better in progressive mode than interlaced. If there is fast motion, it will look better in interlaced mode.

It is never anything to do with your aerial - the decision of whether to choose i or p mode for a group of pictures is taken by the encoding and multiplexing hardware in London (and the BBC's backup location somewhere in the Midlands). For BBC One Northern Ireland HD, and UTV HD, a lightly-compressed high-bitrate signal is sent to the code-and-mux centre for compression and multiplexing. The resulting multiplex is sent back to Divis, where Service Information for the other multiplexes is added. It is then transmitted from Divis and carried via line feeds to Limavady and Brougher Mountain, which also transmit it. The other, relay, transmitters receive off-air from one of those three and retransmit. (Similarly, BBC One NI and BBC Two NI in standard definition are sent to the BBC's code-and-mux centres, while UTV and UTV+1 in SD are sent to ITV/C4 facilities elsewhere in London.)

The reason code-and-mux is done in England is simply that the majority of channels on most of the multiplexes only have one version for the whole UK, mostly played out or originated in London, and it makes more sense to bring in the few differences rather than send out the greater amount of content that is the same. Also, the same content is uplinked to satellites for satellite reception, where all the content for a single transponder has to be combined into one multiplex and uplinked from a single location.

The raw, uncompressed data rate for 1080p25 is the same as for 1080i50. 1080p25 means that 1080 lines are refreshed in full 25 times per second, taking 1/25th of a second, while 1080i50 means that half of the 1080 lines are refreshed in 1/50th of a second, followed by the other half in the next 1/50th of a second. In both modes, any specific line is only refreshed 25 times per second. 1080p50 doubles that to 50 times per second. Much equipment drops the '50' from the end of the indication and just reports 1080i or 1080p.

When a GoP is encoded progressively, the receiver can still send it on to the TV in interlaced mode: it just sends the lines in a different order to how it received them. There is no loss in picture quality and no difference in the apparent motion of the picture.

It may be possible to set up your receiver to send 1080p50 to the TV, if both support it. To receive the 'HD Ready' or 'HD TV' logos, and even the 'Full HD Ready' or 'Full HD TV' logos, the TV only has to support 1080i50 input - it does not have to support 1080p50. They only have to support 1080p50 in order to receive the 'HD Ready 1080p' or 'HD TV 1080p' logos. (The word 'Full' indicates that the TV itself has 1080 display lines, without that word it might have only 720 lines.) 

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Mike Dimmick's 2,486 posts GB flag
Thursday, 8 November 2012
4:30 AM

Hi i live in Blackrock, Co.Louth. I am using a wideband aerial which i mounted in the loft, but can not get any luck in keeping up signal from Divis. My mate lives only 3 miles away in dundalk and hes getting signal without any amplifiers at all.
I have tried adding 2 differnet masthead amplifiers but still no joy.

Anybody having any ideas as to what i am doing wrong?

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Keith's 3 posts IE flag
John Durrell
9:04 AM

Many thanks to Mike Dimmick for his very detailed post. From what Mike has said it seems to me that the interaction of the TV and external i-Can receiver is the issue. The Sharp Aquos TV was bought in 2007 and plays blurays perfectly well in 1080p but I suppose it is getting a pure signal. From what Mike has said the broadcast signal is slightly different and I imagine that the technology in the TV cannot cope with this. The answer seems to be a new TV when this one 'dies'. Thanks agin Mike for all your help. I can now stop worrying about aerials.

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John Durrell's 4 posts GB flag
John's: mapJ's Freeview map terrainJ's terrain plot wavesJ's frequency data J's Freeview Detailed Coverage
Dave Lindsay

10:04 AM

Keith: Divis uses only Group A channels and wideband yagi aerials are less efficient on those channels.

Use a Group A aerial:

Rowridge Transmitter

Digital TV Transmitters

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Dave Lindsay's 5,724 posts GB flag
Peter Henderson

1:12 PM

Keith: I'd also think about getting the aerial mounted outside on the chimney. It should make quite a bit of a difference.

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Peter Henderson's 240 posts GB flag
6:08 PM

Keith: My mother lives in Blackrock and is picking up all freeview muxes from Divis on a chimney mounted group A aerial.

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David's 1 post GB flag
Friday, 9 November 2012
5:15 AM

Thanks guys. I'll have to get myself a group a aerial.
Another question, to get the saorview signal from Claremont Carn I will need a c/d group aerial, is this correct or will I be able to continue using my wideband aerial (which is picking up soarview perfectly now) and how do I wire the 2 aerials into 1 coax cable??

Thanks again for your help.

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Keith's 3 posts IE flag
Dave Lindsay

11:29 AM

Keith: The sensitivity (gain) of an aerial isn't the same across all UHF channels/frequencies. For yagi aerials, the shape of the curve is broadly the same. See here for examples that illustrate my point:

Gain (curves), Again

The gain of wideband yagi aerials on Group A channels is much lower than C/D ones. That is why there is no such thing as a high gain wideband aerial that has "high" gain on Group A channels.

More gain in one direction is simply at the expense of more "loss" in others. So the "beam" of a higher gain aerial is narrower.

If your wideband aerial is sufficient for Clermont Carn, then there is no reason not to continue using it. The reason for suggesting use of a Group A aerial for Divis is because of the lower gain of the wideband aerial on its channels and the poor reception you are experiencing.

You need a diplexer to combine the two feeds:

Online TV Splitters, Amps & Diplexers sales

For Divis and Clermont Carn, get a diplexer that "splits" at C38. This will allow you to receive a multiplex from Divis on C36 should it ever come to fruitition.

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Dave Lindsay's 5,724 posts GB flag
Saturday, 10 November 2012
1:24 AM

Does anyone have any idea why I can get the RTE radio stations via Digital TV but not through my DAB radio?

I live in the Newry area, prior to DSO I could get a very weak signal from the RTE radio stations on my DAB set but it would never tune in. I would get a service not available message.

After the DSO I retuned my DAB radio in the hope of getting a better signal but I have now lost all the RTE channels.

I would appreciate any help thanks.

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MEM's 12 posts GB flag
Dave Lindsay

11:50 AM

MEM: Because the DAB signal and the TV signal are different signals. The TV switchover didn't mean any difference to DAB radio.


Digital Radio Ireland » Can I get DAB

Maybe you need a directional aerial.

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Dave Lindsay's 5,724 posts GB flag
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