HA
I may be about to show my ignorance, but this backup at 27.5W is confusing me. Wouldn't a terrestrial transmitter would require a pre-multiplexed feed, such as they get from the Coding and Mux centre. According to Lyngsat these feeds are DVB-S2 encoded, rather than DVB-T as would be transmitted from a DTT transmitter. That implies that the satellite mux would have to be decoded and recoded (or at least reassembled) at the TX site, particularly as it looks like there are different versions of BBC One in the nations.
I don't think anything too clever happens at the Tx site to use these feeds. Yes, they are in a DVB-S2 wrapper, but I think once decoded to TS level the PIDS/SIDS etc replicate enough of the 'real' CCM feeds, that the cherry picked services (as you say, appropriate versions of BBC 1 and 2) plus the SI data, are then stuffed into a DVB-T encoder, and the domestic receivers are fooled enough to maintain a basic service that replicates the mux ?
It has to work that way, other wise every viewer would have to perform a rescan. I can't find any info
on the scheme, not surprising of course, because you could use the same idea to form 'pirate' broadcasts.
Yep - think the are flagged as data rather than video precisely to allow them to be more "DVB-T/T2" than DVB-S2 video?
Also it dosent show up being tuned in automatically on set top boxes as it's not a regular channel, so never shows up on listing.
harshy
Founding member
There are two satellites carrying domestic channels - one FTA with a tight beam (Astra 28.2) and one encrypted with a much wider beam (and used as a backup to fibre feeds to the UK terrestrial transmitter network)
I may be about to show my ignorance, but this backup at 27.5W is confusing me. Wouldn't a terrestrial transmitter would require a pre-multiplexed feed, such as they get from the Coding and Mux centre. According to Lyngsat these feeds are DVB-S2 encoded, rather than DVB-T as would be transmitted from a DTT transmitter. That implies that the satellite mux would have to be decoded and recoded (or at least reassembled) at the TX site, particularly as it looks like there are different versions of BBC One in the nations.
I don't think anything too clever happens at the Tx site to use these feeds. Yes, they are in a DVB-S2 wrapper, but I think once decoded to TS level the PIDS/SIDS etc replicate enough of the 'real' CCM feeds, that the cherry picked services (as you say, appropriate versions of BBC 1 and 2) plus the SI data, are then stuffed into a DVB-T encoder, and the domestic receivers are fooled enough to maintain a basic service that replicates the mux ?
It has to work that way, other wise every viewer would have to perform a rescan. I can't find any info
on the scheme, not surprising of course, because you could use the same idea to form 'pirate' broadcasts.
Yep - think the are flagged as data rather than video precisely to allow them to be more "DVB-T/T2" than DVB-S2 video?
Also it dosent show up being tuned in automatically on set top boxes as it's not a regular channel, so never shows up on listing.
