BBC Scotland thread

The same applies to some isolated valleys in The Lake District, the best TV signal available is from Divis. There's nothing magic about digital signals that make them get to places analogue cannot reach. It'll be a matter of economics, rather than engineering why most of these areas cannot be served with the correct regional TV. If anything satellite is a better platform to achieve that.

When I got my first digital radio, I recall reading that one of the ways it was better was that signals reached further than FM, something to do with the way they bounced off buildings better than FM signals? (I may be misremembering). Was this untrue?

DAB relies upon SFNs (Single Frequency Networks) where the same mux is carried on the same frequency on all of the transmitters. The diverse reception of one or more transmitters ( within certain limits) results in a positive additive effect on the received signal. The same applies to a reflected signal, that on analogue TV resulted in a ghost image, and on FM radio results in distortion. DTT can also operate as an SFN, indeed the Dutch PSB mux does, however using an SFN also reduces the payload of a mux, there’s a trade off between maximum separation of transmitters in an SFN, and payload ( amount of bandwidth) UK DTT only allows for SFNs of around 20 miles or so, and some do exist here. It’s a complicated subject, but SFNs wouldn’t help the problem Robert mentioned

Thanks Steve, Tony and Mark for your comments. Not sure I understand why BBC NI pres would've been unmanned. The break apparently happened during an episode of 'The Rockford Files', which I assume would've been evening/late-evening. I know that BBC NI pres used to cover introductions to local programmes only for a portion of the 70s - as well as inserting promos for local programmes. That said, the pres suite would have been manned from early evening to closedown, as far as I know. Could be wrong. They'd usually take the network ident and announcer into networked programmes. Not sure at what point in the 70s they began covering all evening junctions locally. But if Belfast was unmanned I can understand why RBS would've kicked in.

For as long as I used to be able to take a nosey at the VBI - we'd be talking as far back as early 80s - BBC NI did have their own ID there. The local VBI ID would usually appear when they put the local desk in circuit just before the next junction. In those days there was a line of dots underneath the teletext lines. Towards the right side, there was a group of dots that seemed to reflect the countdown to the next programme. I always assumed this line of data was Presfax. This line of data disappeared when BBC NI were in circuit. If BBC NI was still on air late at night, after network closed down, the only visible indication of loss of network feed was the loss of Ceefax signal. An apology Ceefax page was introduced c. 1987 to cater for such scenarios. Of course, the Ceefax logo changed in 1989 but this apology page was never updated - the 1983 Ceefax logo remained on that page right up to analogue switch off. And bizarrely, BBC Two's in-vision Ceefax slide featured the 1983 logo for a number of years until 2012.

If BBC One NI closed down around the same time as network - but BBC One Scotland was still on air, the NI transmitters tripped over to BBC One Scotland when the network feed was shut down. This happened quite a lot in the 1990s - picture was a little fussy. I have some examples in my archive [the BBC Two Scotland clock at the bottom of this page: http://thetvroom.com/bbc-uk/bbc-2-1991-02-id-010.html is from such an RBS transmission]. In the mid-1990s, when Divis suffered a power failure, I was in the north west of NI at the time and we received BBC Scotland on both channels. No idea what viewers in Belfast were receiving if Divis had no power. But the Limavady and Derry relay at Sheriff's Mountain were pumping out BBC Scotland.

I've dug out the details

Limavady was RBL Divis, and RBS Black Mountain via an SHF link from there, B.Mtn received RBS Cambret Hill [1], The Derry relay was RBL Limavady anyway, as was Strabane. Brougher Mountain was RBL Divis, and RBS Strabane.

The RBL link from Divis was a particular challenge, because Divis and BM were on adjacent frequencies, so
receiving the weak signal from Divis would have required filtering of BM's own transmissions. You can see the two RBL 'Trough' antennas in the picture below, with shielding above them to reduce pick up from the Tx antennas at the top of the mast. On the right are a pair of Vert Pol RBS troughs looking at Strabane. (The second Strabane trough is very low down)

http://admin.mb21.co.uk/tx/userimages/2164orig.jpg

[1] Edit to correct RBS source for Limavady, I mis-read Black Hill for Black Mountain !

Thanks for taking the time to map out the detail Mark - and particularly for the info re the antennas on that mast. Very interesting.

So, following the logic of the chain you've described, if I was watching pictures from the Derry transmitter at Sheriff's Mountain, the pictures were supplied to Derry by Limavady. As Limavady had lost its line from Divis, it should've switched to RBS mode. RBS for Limavady was Black Mountain, which had also lost its feed from Divis and would've been in RBS mode itself and picking up signal from Cambret Hill. Hence why we were seeing BBC Scotland in the Derry area. The vast majority of viewers in the Belfast area - who are served by Divis (which was out due to power blackout) - would've lost service completely, presumably?

Going incredibly off-topic here, a Ceefax apology page with the 'new' logo did exist, which would presumably be used if the inserters in London lost their data feed. This example was broadcast during some overnight tests in 2010 (and is a cameraphone shot taken in CCA)

Yes. Black Mountain, which was the old 405 line VHF site for UTV, did (still does) have a low power UHF relay
to serve dwellings very close by. I presume the RBS route for Limavady was established there, because it offered resilience should there be a major problem at either Divis or BBC Belfast.

I'm not aware it had any equipment or antennas installed to enable it to take the place of Divis should Divis
suffer a catastrophe, so as you say no one in the Divis service area would have received anything, only Limavady, Derry, and Brougher Mountain (and all their relays).

I've seen that particular apology page - or something very similar to it - on a couple of occasions. And If I recall correctly, the cause was computer problems at Ceefax HQ at Television Centre. From what I could tell at the time, the page was generated in London - from the same equipment that the main service was pumped out from (the functioning clock is an indication of this) - and was visible in the regions. I'm nearly sure that on one of these occasions, large groups of pages were unavailable.

The gear used to transmit the apology message in the event of a complete loss of Ceefax feed (the one featuring the 1983 logo) was a separate mechanism and was never updated, to the best of my knowledge. I can't recall where that particular Ceefax apology message originated from. I'm nearly sure I was told in the past that a box was installed at main transmitter sites to put out this page if the main Ceefax feed disappeared. But my memory on this is very hazy. I didn't note down the correct technical detail. If anyone knows, it'd be great to know for certain.

Turning away from transmitter etc to pres; Scot Squad has a new sting. ( has anyone spotted any others)

New information has come about regarding the BBC Scotland channel.

Programmes could start as early as midday, if the BBC wants to broadcast events such as sport programming - earlier than the start up time of 7pm.

The channel will be SD only on traditional TV platforms. iPlayer will be the only way to access HD content from the new channel.

Discussions were already underway with BBC Three and Four controllers about content for the new channel.

BBC Two Scotland would close as an opt-out service for BBC Two.

The BBC wants to launch BBC Scotland on LCN 9 on Freeview, pushing BBC Four SD down to the 90s.

Link: http://www.a516digital.com/2017/11/bbc-scotland-channel-ofcom-invites.html

Can’t wait to watch it in glorious standard definition