Above and beyond: Keeping TV and radio services on air

That's interesting. Does that mean that there is multiplexing kit on site to reassemble a mux?

At least there would need to be that. I guess either they are CBR-enough to allow a mux to be assembled. (CBBC, BBC News Channel, BBC Parliament and CBeebies/BBC Four in SD could be statmuxed together, but BBC One SD and BBC Two SD would need to be CBR to allow the national variations to take place?) or they are decoded and recoded and muxed for SD?

There is. I've seen it at a Tx site, some DVB-S receivers with BISS decoders, and a crate to mux it all up.
The static SI tables and associated stuff is generated at the Tx site anyway, the code and mux for the primary feeds is
done remotely at the various CCM sites, and the muxes sent ready assembled to each Tx. So, you've only (he says !) got to replace the A and V components, and EPG/EIT data. I presume the Red Button stuff is replaced with null packets, or a holding page. I'd love to see what a mux running on this RBS system looks like and behaves as far as receivers are concerned.

I've analysed the signal for this transponder (11495V) in TransEdit on my PC - all services other than the four national versions of BBC One SD are stat-muxed. The video for all the BBC Ones runs in CBR at ~3.3Mbps.

Fairly easy to decrypt and assemble the muxes at a transmitter site, they wouldn't need re-encoding.



There is MHEG data present in the stream, not sure if this is full red button or just the "channel off-air"/radio station style of slates. BBC Alba is just an MHEG slate by the look of the stream, there's certainly never a video stream for it - so any transmitter in Scotland using this feed will be missing it.

There's no EIT data in the satellite feed (not in a standard DVB format in any case), so does this get "cached" for the EPG, etc. to be available for a certain amount of time after satellite fallback is triggered at a relay transmitter from a time where they can receive their off-air source? Or is there just no EPG during the times where the satellite feed is in use?

There must be using dvb-s2 now I need to check if it is. The bitrate is the same as 28.2e and some channels are running on funny resolutions like 704x576 I think there’s one at 544x576.

704x576 isn't a funny resolution - it's the nearest MPEG multiple to 702x576 which is the 4:3 or 16:9 picture area (the extra 9 samples each side to generate 720x576 are to avoid clipping overshoots and undershoots on an analogue round-trip, and because it means we can have the same line widths in 525 and 625)

Thanks noggin I am guessing the stuff on 28.2e must be fibered there’s no bbc News hd on 27.5w just the SD version.

There’s no epg data which would suggest if they had to revert to this backup there’s no epg maybe?

Presumably that's because BBC News HD isn't on a BBC DTT Mux, it's on Com 7

Yes. The Beeb only back up PSB 1, and PSB 3 at 27.5w (the latter means that the HD versions of ITV, 4 and 5 are also backed up)

Not sure your point about fibred?

The 27.5W is a backup for the BBC operated Freeview muxes (PSB1 and PSB3). As BBC News HD isn't on PSB3 - it wouldn't be on the 27.5W backup.

(It's on one of the two HD COM muxes - it was COM7 but I think there is a shuffling happening between 7 and 8 )

I don't know what D3/4 who operate (or operated) PSB2 do for their resilience, nor do I know what Arqiva do for COM4-8.

BBC News HD - COM7; BBC Four HD /CBeebies HD will be COM8 only from later this week following a one week transition period.


COM4 (SDN from ITV plc) used to be fed from satellite (I seem to recall it might have been Eutelsat W2 at 16E - the satellite failed one night taking all SDN Freeview channels off-air). It and all COM muxes are now fed by fibre to the transmitters - there's no middle of nowhere relays that haven't been fibred to worry about for the COM muxes.

Sorry - I keep forgetting about the SDN mux being a COM but not owned by Arqiva. It's a bit of an oddity.