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noggin14,216 posts since 26 Jun 2001

I was going by the opt switch being replaced by Sky DSAT receiver.


Yes - but that's not a signal provided by a third party. The BBC services received by Sky (and Freesat) receivers are not uplinked or 'provided' by Sky. They are simply receiving signals broadcast by the BBC in a format that Sky receivers can receive (i.e. the BBC and Sky/Freesat co-operate on EPG data provision so that BBC transponders, uplinked by the BBC - or companies sub-contracted by the BBC - carry Sky and Freesat EPG data, and automatically map the correct services to agreed channel numbers at the bouquet level etc.)

This is very different to the US model, where all services on DIrecTV and Dish are, I believe, uplinked by DirecTV or Dish, and broadcasters don't uplink their own services to these platforms. (The US satellite services are far more like 'cable headends in the Sky' than the UK services. Other European countries follow the US model more though.)
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London Lite gave kudos
noggin14,216 posts since 26 Jun 2001
Most if the time Sandy Heath was fed by the Radio link from Norwich .
AT some time before the opt Cambridge would signal to feed the Norwich output (rather than The contribution microwave from FRV Luton Nhampton) to it .

Often only a few seconds before the opt (if the FRV was in the west of the patch and doing a live before the opt)...


Once the incoming feed from Sandy Heath had BBC One Norwich on it, you'd then hit another button, which locally triggered the BBC Cambridge SPG to Genlock to incoming BBC One Norwich (So that BBC One Norwich and local sources were synchronous on the Cambridge vision mixer)

This was to avoid adding another frame of delay I believe - which would have been the case if Cambridge had been free-running and BBC One Norwich had been synchronised incoming to Cambridge.

Quote:

Put that through the mixer and then signal to feed Sandy by the return circuit ...
and signal to feed the transmitter from Cambridge ....


Yes - the third button (which was key-locked - eventually) remotely switched the Sandy Heath transmitter between its feed of BBC One Norwich and the feed from the Cambridge gallery.

This was always a synchronous cut (no frame rolls), but the two versions of BBC One (BBC One Norwich and BBC One Norwich via Cambridge) were relatively delayed by a couple of frames.

I was told this was due to a PAL composite Tektronix synchroniser at Sandy Heath synchronising BBC Cambridge gallery incoming with the BBC One Norwich local feed at the transmitter. (PAL synchronisers could introduce more delay than component ones because of 4-field/8-field issues?)

[quote]
all that switching was in the SIS domain and I think if there had been
a Tek synchroniser it did not work well !!! So the opt switch was asynchronous..
[quote]

In 6 months of carefully watching the soft-opt point I never saw an asynchronous cut, but this was before the system was re-engineered for DTT (where a relatively complex system was installed that allowed DVB-T opts in Norwich and Cambridge and put a vision circuit from Norwich to Cambridge (which previously wasn't an option) that was available when Norwich hadn't opted out (when Norwich opted out this circuit carried Norwich's output to Cambridge and triggered an opt-out in Cambridge too I believe)...

Quote:

( and a relay in any case)
Then you could gracefully fade over from Norwich to local sources.


Yes - genlocking BBC Cambridge to BBC One incoming ensured all local sources were locked and synchronous with incoming BBC One, so you could mix, fade down and up without frame rolling etc.

[quote]
Thus having a permanent feed that never opted at Sandy was seen
to be a great improvement

As the analogue was being fed by a digital distribution
.. the Network recall was done as it is for all digital services in coding and mux ...
its sort of how buddying works after all.

Quote:

And I'm fairly certain that a sky box did 14:9 despite it being WSS not AFD.


Consumer Sky boxes were either permanent 12F12 centre cut, or switched between 12F12 and 16L12, driven by the MPEG2 header switching (Sky boxes didn't insert WSS either, though some passed on WSS (some blanked it) if it was present in the received video. ISTR that the Sky SD chains had ARCs in their chains upstream of the MPEG2 encoder - that were fed the permanent 16:9 feed (containing 12P16 or 16F16 sources) of BBC One - and then dropped in a 12F12 ARC when 12P16 was signalled, and stayed in passthrough when 16F16 was signalled. The 12F12 ARC signalled to the MPEG2 encoder downstream that the source was now 12F12, whilst in bypass it signalled 16F16.

There wasn't a 14L12 implementation on consumer Sky boxes. (Just as there isn't a 12P16 option on Sky HD boxes for 4:3 SD output in 16:9 HD...)
Rkolsen2,602 posts since 20 Jan 2014
BBC World

I was going by the opt switch being replaced by Sky DSAT receiver.


Yes - but that's not a signal provided by a third party. The BBC services received by Sky (and Freesat) receivers are not uplinked or 'provided' by Sky. They are simply receiving signals broadcast by the BBC in a format that Sky receivers can receive (i.e. the BBC and Sky/Freesat co-operate on EPG data provision so that BBC transponders, uplinked by the BBC - or companies sub-contracted by the BBC - carry Sky and Freesat EPG data, and automatically map the correct services to agreed channel numbers at the bouquet level etc.)

This is very different to the US model, where all services on DIrecTV and Dish are, I believe, uplinked by DirecTV or Dish, and broadcasters don't uplink their own services to these platforms. (The US satellite services are far more like 'cable headends in the Sky' than the UK services. Other European countries follow the US model more though.)

Okay, I guess I am surprised that they are also already taking a compressed feed in one codec to transmit in another.
Yes, DirecTV and Dish have their own headend and uplink everything at a central location. Each TV market that they uplink from (some markets aren’t uplinked at all - but most of the 210 DMAs are) they have a receive location that takes the off air signals from stations which are sent to the uplink facilities.
Don’t let anyone treat you like you’re a VO/SOT when you’re a PKG.
noggin14,216 posts since 26 Jun 2001

I was going by the opt switch being replaced by Sky DSAT receiver.


Yes - but that's not a signal provided by a third party. The BBC services received by Sky (and Freesat) receivers are not uplinked or 'provided' by Sky. They are simply receiving signals broadcast by the BBC in a format that Sky receivers can receive (i.e. the BBC and Sky/Freesat co-operate on EPG data provision so that BBC transponders, uplinked by the BBC - or companies sub-contracted by the BBC - carry Sky and Freesat EPG data, and automatically map the correct services to agreed channel numbers at the bouquet level etc.)

This is very different to the US model, where all services on DIrecTV and Dish are, I believe, uplinked by DirecTV or Dish, and broadcasters don't uplink their own services to these platforms. (The US satellite services are far more like 'cable headends in the Sky' than the UK services. Other European countries follow the US model more though.)

Okay, I guess I am surprised that they are also already taking a compressed feed in one codec to transmit in another.
Yes, DirecTV and Dish have their own headend and uplink everything at a central location. Each TV market that they uplink from (some markets aren’t uplinked at all - but most of the 210 DMAs are) they have a receive location that takes the off air signals from stations which are sent to the uplink facilities.


There is no recompression going on in this example. The DSat receiver was a short term solution to feed the analogue (i.e. uncompressed) composite PAL transmitter prior to analogue switch off (rather than re-routing the microwave circuits when the BBC moved the Cambridge operation to a new building). It was pretty much the same quality as if someone has plugged a Sky box RF modulator output directly into their TV, albeit with NICAM stereo audio (not mono - as domestic RF modulators were)

AIUI a similar approach was used to feed the BBC One Jersey transmitter when BBC Channel Islands relocated (and the opt-out chain was via Plymouth)

The DVB-T transmissions were (and are) coded and muxed in central locations to allow for stat muxing, and don't have an intermediate codec. They are fed via fibre from the coding and mux locations, I guess sending an ASI stream? (The BBC One network feed that is the 'back stop' of each opt-switch that reaches the regional centres is 9Mbs MPEG2, however the return leg to coding and mux is uncompressed SDI-rate).

I guess it was easier and cheaper to source a DVB-S off-air feed with a Sky received at Sandy Heath than install gear to decode the incoming DVB-T transport stream to feed the BBC One analogue TX from the BBC One DVB-T feed sent to the transmitter?
Last edited by noggin on 13 May 2019 9:47am
Technologist23 posts since 10 Oct 2018
London London

Yes - but that's not a signal provided by a third party. The BBC services received by Sky (and Freesat) receivers are not uplinked or 'provided' by Sky. They are simply receiving signals broadcast by the BBC in a format that Sky receivers can receive (i.e. the BBC and Sky/Freesat co-operate on EPG data provision so that BBC transponders, uplinked by the BBC - or companies sub-contracted by the BBC - carry Sky and Freesat EPG data, and automatically map the correct services to agreed channel numbers at the bouquet level etc.)

This is very different to the US model, where all services on DIrecTV and Dish are, I believe, uplinked by DirecTV or Dish, and broadcasters don't uplink their own services to these platforms. (The US satellite services are far more like 'cable headends in the Sky' than the UK services. Other European countries follow the US model more though.)

Okay, I guess I am surprised that they are also already taking a compressed feed in one codec to transmit in another.
Yes, DirecTV and Dish have their own headend and uplink everything at a central location. Each TV market that they uplink from (some markets aren’t uplinked at all - but most of the 210 DMAs are) they have a receive location that takes the off air signals from stations which are sent to the uplink facilities.


There is no recompression going on in this example. The DSat receiver was a short term solution to feed the analogue (i.e. uncompressed) composite PAL transmitter prior to analogue switch off (rather than re-routing the microwave circuits when the BBC moved the Cambridge operation to a new building). It was pretty much the same quality as if someone has plugged a Sky box RF modulator output directly into their TV, albeit with NICAM stereo audio (not mono - as domestic RF modulators were)

AIUI a similar approach was used to feed the BBC One Jersey transmitter when BBC Channel Islands relocated (and the opt-out chain was via Plymouth)

The DVB-T transmissions were (and are) coded and muxed in central locations to allow for stat muxing, and don't have an intermediate codec. They are fed via fibre from the coding and mux locations, I guess sending an ASI stream? (The BBC One network feed that is the 'back stop' of each opt-switch that reaches the regional centres is 9Mbs MPEG2, however the return leg to coding and mux is uncompressed SDI-rate).

I guess it was easier and cheaper to source a DVB-S off-air feed with a Sky received at Sandy Heath than install gear to decode the incoming DVB-T transport stream to feed the BBC One analogue TX from the BBC One DVB-T feed sent to the transmitter?


The DTT mux does not have Teletext subtitles in it as was required for analogue ..... but the DSAT does for Sky boxes ... hence the use of a DSAT feed .

The Channel isles feed was all due to the loss if the microwave link frequencies due to the French !! So a number of E1 circuits were used to feed the NICAM Radio streams and a cue visionfeed with a very full VBI with both BBC one and BBC two Ceefax in it going one way and a 8 Mbit/sec CI studio output with opt signalling going the other.
Ceefax etc was bridged

The regions are fed ST 2022-6 SDI over IP both to and from the regional opt switch and then coded and muxed and then given to Arqiva at ASI who I think use ST2022-2 IP to the transmitter
Rkolsen2,602 posts since 20 Jan 2014
BBC World
I’m confused wouldn’t rebroadcasting a feed designed for viewers in one format to another reduce the quality? From what it sounds like that briefly they took the one signal from Sky DSAT or FreeSat to feed the transmitter. I take it the quality from the satellite wouldn't be the full quality that it would be if it was microwaved to the transmitter.

I guess we one way of what I’m saying is that it’s like playing out programs from a VHS tape when you have the original .mxf format.
Last edited by Rkolsen on 13 May 2019 2:20pm
Don’t let anyone treat you like you’re a VO/SOT when you’re a PKG.
Markymark6,519 posts since 13 Dec 2004
Meridian (North) South Today
I’m confused wouldn’t rebroadcasting a feed designed for viewers in one format to another reduce the quality? From what it sounds like that briefly they took the one signal from Sky DSAT or FreeSat to feed the transmitter. I take it the quality from the satellite wouldn't be the full quality that it would be if it was microwaved to the transmitter.


No it certainly wasn't. Though, as I said up thread, when ITV/Arqiva did the same thing in the South West of England, they also increased the bit rate (and the resolution) of the satellite stream to make it a better quality source.

However, in the case of BBC East and ITV Westcountry it was only a temporary measure for a couple of years, to
keep the analogue feeds going until DSO. For any longer period, a more conventional arrangement involving microwave links and fibre circuits would have been implemented, but the costs didn't stack up for the sake of a couple of years. Both these schemes were provided, because in both cases the local studios had been relocated.

The same sort of applied to the Channel Islands. Though both ITV and C4 had switched to a 'proper' fibre circuit in the 90s, so were not affected by the SHF shortage. The D-Sat solution for BBC 1/2 lasted from 2003, to DSO in 2011
Markymark6,519 posts since 13 Dec 2004
Meridian (North) South Today

The Channel isles feed was all due to the loss if the microwave link frequencies due to the French !! So a number of E1 circuits were used to feed the NICAM Radio streams and a cue visionfeed with a very full VBI with both BBC one and BBC two Ceefax in it going one way and a 8 Mbit/sec CI studio output with opt signalling going the other.
Ceefax etc was bridged


The NICAM feeds (that had been provided since the 80s on a special UHF beam on a special frequency from Stockland Hill (received using the same Rx rig on Alderney as was used for analogue TV) had to cease in the early 00s, because that frequency (UHF Ch 28 IIRC) was reallocated for DTT use at Stockland Hill. So, it made sense to incorporate them in the new arrangement for TV.
Rkolsen2,602 posts since 20 Jan 2014
BBC World
I’m confused wouldn’t rebroadcasting a feed designed for viewers in one format to another reduce the quality? From what it sounds like that briefly they took the one signal from Sky DSAT or FreeSat to feed the transmitter. I take it the quality from the satellite wouldn't be the full quality that it would be if it was microwaved to the transmitter.


No it certainly wasn't. Though, as I said up thread, when ITV/Arqiva did the same thing in the South West of England, they also increased the bit rate (and the resolution) of the satellite stream to make it a better quality source.

However, in the case of BBC East and ITV Westcountry it was only a temporary measure for a couple of years, to
keep the analogue feeds going until DSO. For any longer period, a more conventional arrangement involving microwave links and fibre circuits would have been implemented, but the costs didn't stack up for the sake of a couple of years. Both these schemes were provided, because in both cases the local studios had been relocated.

The same sort of applied to the Channel Islands. Though both ITV and C4 had switched to a 'proper' fibre circuit in the 90s, so were not affected by the SHF shortage. The D-Sat solution for BBC 1/2 lasted from 2003, to DSO in 2011

Apologies, I didn’t see your post. Just seemed like an odd way to feed a transmitter for a period of time and obviously took a while to get my head around.
Don’t let anyone treat you like you’re a VO/SOT when you’re a PKG.