Building Communal Muxes

prpr

Well-Known Member
The spectrum for a DVB mux is practically flat from nominal-4MHz to nominal+4MHz, because the channel is split into (IIRC) 1024 sub-channels each modulated with 1/1024th of the data stream which are then combined at the receiver into a single serial stream. One single service wouldn't need as much data as 20 or so services on a single mux, so I was simply speculating that there wouldn't need to be so many sub-channels and what sub-channels there are might be concentrated near the centre frequency.
It doesn't work like that. Go and read the Wikipedia pages on DVB-T, DVB-T2 and OFDM if you want your mind blown.
 

Luke

Well-Knwοn Мember
It will be 8MHz wide like any other mux in the UK
You're ahead of your time.
COM8 isn't switched off until tomorrow, and that is 7Mhz. When COM8 was changed from 8Mhz the FEC was also changed from 2/3 to 1/2, which is why the capacity on COM8 reduced from 38.6 Mb/s to 26.9 Mb/s.
 

Owen Smith

Active Member
You're ahead of your time.
COM8 isn't switched off until tomorrow, and that is 7Mhz. When COM8 was changed from 8Mhz the FEC was also changed from 2/3 to 1/2, which is why the capacity on COM8 reduced from 38.6 Mb/s to 26.9 Mb/s.
Please quote your evidence for COM8 being 7MHz wide. COM7 and COM8 reduced in bandwidth due to the guard interval being increased to allow them to be SFNs. They're both 8MHz wide as expected by UK tuners. The HDR Fox T2 has to be told if a mux is 7MHz wide rather than 8 when tuning to it.
 

Luke

Well-Knwοn Мember
Please quote your evidence for COM8 being 7MHz wide. COM7 and COM8 reduced in bandwidth due to the guard interval being increased to allow them to be SFNs. They're both 8MHz wide as expected by UK tuners. The HDR Fox T2 has to be told if a mux is 7MHz wide rather than 8 when tuning to it.
https://whytetechnologies.com/newsInfo/newsFullDetails/We're-here-to-help-125

There is a discussion on why when tuning the 8Mhz setting still has to be used at:
 

Owen Smith

Active Member
https://whytetechnologies.com/newsInfo/newsFullDetails/We're-here-to-help-125

There is a discussion on why when tuning the 8Mhz setting still has to be used at:
Which makes it clear it wasn't a proper 7MHz Mux, but flagged as 8MHz so UK receivers would tune to it while only occupying 7MHz of spectrum. Hence needing the FEC changed so the 1MHz of noise could be tolerated. In other words, a total bodge. And give it changed to that on 10 Feb 2020 and is now off air, it only lasted 4 months so it seems like a complete waste of time to me. It would have been better to shut it down in February.
 

prpr

Well-Known Member
Please quote your evidence for COM8 being 7MHz wide.
Luke is right. I don't have a reference to hand, but it's currently true. It wasn't always like this.
COM7 and COM8 reduced in bandwidth due to the guard interval being increased to allow them to be SFNs.
True but irrelevant to the point.
They're both 8MHz wide as expected by UK tuners.
No, one is 8 MHz and the other is 7.
The HDR Fox T2 has to be told if a mux is 7MHz wide rather than 8 when tuning to it.
No it doesn't. Mine was never told and it still worked. In fact I haven't retuned it since it was 8 MHz because the Network name still says West rather than Com78 National.
 

Owen Smith

Active Member
At least now COM7 can be changed to 55+ (if it isn't already on that) to sit better within the 700MHz mobile TX/RX guard space. Though why equipment these days needs such a huge guard band beats me.
 

Owen Smith

Active Member
No, one is 8 MHz and the other is 7.

No it doesn't. Mine was never told and it still worked. In fact I haven't retuned it since it was 8 MHz because the Network name still says West rather than Com78 National.
COM8 was never a proper 7MHz mux. From 10 Feb 2020 it was flagged as 8MHz but TX'd only on 7MHz of that and needed a robust FEC change so the receivers didn't get upset by all the noise on the top 1MHz. That is a hideous bodge, not a 7MHz mux. I'm glad it didn't last and has been shut down.

And if a516Digital had still been operating, I would have known about it at the time. I mourn the loss of such an excellent source of news, that has not been replaced.
 
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Owen Smith

Active Member
That won't happen. Any + or - offsets that were there on things subject to the 700 MHz clearance shuffling have been removed.
Last time I looked Sandy Heath still used 21+ to give some guard at the bottom end. Or has that gone too?

The trouble these days is good technical information is hard to find, all the decent sources I used to follow have dried up.
 

prpr

Well-Known Member
Last time I looked Sandy Heath still used 21+ to give some guard at the bottom end. Or has that gone too?
It still does, but that channel wasn't subject to a move.
What I am saying is that if a mux. moved channel, then it would not have an offset at the new location. If it didn't move channel, then it may or may not have had its offset removed.
I know this because I allowed for it in tunefix, but have never used it for these clearance moves.
 
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