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Manchester - Local Freeview Multiplex - Information Thread |
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#51 |
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Forum Member
Join Date: Dec 2008
Location: East Midlands
Posts: 5,204
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Quote:
movies4men
But thanks for letting us know first. |
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#52 |
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Forum Member
Join Date: Feb 2003
Posts: 1,256
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Quote:
Greebo make sure you post in the Changelog.
PID found: 0 (0x0000) [SECTION: Program Association Table (PAT)] |
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#53 |
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Forum Member
Join Date: Jun 2005
Location: Guildford / Crystal Palace
Posts: 13,114
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Your PID 38 will be either subtitles or audio description for Channel M
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#54 |
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Forum Member
Join Date: May 2002
Location: Beds (Sandy Heath TX)
Posts: 8,852
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Quote:
High profile! Ha! I'd like to see how this regional trial goes. I can't see people dying to see this channel...
So, yeah, maybe not "high profile" as such, but certainly a reasonable addition. If it was nationwide I doubt there would be many complaints! |
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#55 |
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Forum Member
Join Date: Sep 2001
Location: Manchester
Posts: 348
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Quote:
Your PID 38 will be either subtitles or audio description for Channel M
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#56 |
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Forum Member
Join Date: Sep 2001
Location: Manchester
Posts: 348
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Quote:
By 6pm, the following was detected:
[7002]:762000000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_3_4:FEC_1_2:QAM_16:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:2323:2324:28674 |
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#57 |
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Forum Member
Join Date: Jun 2005
Location: Guildford / Crystal Palace
Posts: 13,114
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Quote:
It's the PCR for 28673 (Channel M).
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#58 |
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Forum Member
Join Date: Feb 2003
Posts: 1,256
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Quote:
Interesting, shows up as QPSK 1/2 1/32 here.
Stream code rate (hi prio): FEC 1/2I have no idea where the linux_dvb_apps scan command gets the extra 3_4 from. It gets other muxes correct eg: BBC ONE:801833000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_2_3:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:101:102:4168 |
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#59 |
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Forum Member
Join Date: Feb 2003
Posts: 1,256
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Quote:
It's the PCR for 28673 (Channel M).
Quote:
Normally the PCR uses the video PID.
------------------------------------------------------------So this mux does that differently to the other 6. |
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#60 |
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Forum Member
Join Date: Sep 2001
Location: Manchester
Posts: 348
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They are doing it all themselves, so I suppose it's likely there are a few subtle differences between them and the big boys. I'm not aware of there being any problem using different PIDs for video and PCR though. They appear to be using separate PCR PIDs on DSAT.
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#61 |
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Forum Member
Join Date: Jul 2007
Posts: 10,875
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If I remember correctly, the coverage of the Channel M mux could have be improved after The Wrekin switchover, which has now taken place. Has there been any change to the Channel M coverage yet?
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#62 |
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Forum Member
Join Date: Jun 2005
Location: Guildford / Crystal Palace
Posts: 13,114
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Quote:
If I remember correctly, the coverage of the Channel M mux could have be improved after The Wrekin switchover, which has now taken place. Has there been any change to the Channel M coverage yet?
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#63 |
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Forum Member
Join Date: Jun 2005
Location: Guildford / Crystal Palace
Posts: 13,114
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Quote:
They are doing it all themselves, so I suppose it's likely there are a few subtle differences between them and the big boys. I'm not aware of there being any problem using different PIDs for video and PCR though. They appear to be using separate PCR PIDs on DSAT.
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#64 |
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Forum Member
Join Date: Sep 2001
Location: Manchester
Posts: 348
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Quote:
The only users of separate PiDs for Video & PCR on DTT are some of the Mheg protected adult channels.
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#65 |
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Forum Member
Join Date: Jun 2005
Location: Guildford / Crystal Palace
Posts: 13,114
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Quote:
Interesting, shows up as QPSK 1/2 1/32 here.
![]() A QPSK FEC 1/2 mux only has a capacity of 6Mbps (or 2 SD channels) which explains why MANCHESTERLOVE has had to be removed to accommodate Movies4Men. However they can change the FEC rate up to 7/8 to achieve a bitrate of 10.5Mbps on QPSK offering maybe 3 video streams and a few GMG radios. As soon as they need more capacity they will have to revert back to 16QAM with a slightly reduced footprint. |
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#66 |
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Forum Member
Join Date: Feb 2003
Posts: 1,256
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Quote:
I have no idea where the linuxtv_dvb_apps scan command gets the extra 3_4 from.
Transport_stream_ID: 28672 (0x7000) then as actually locked by the tv card: Current parameters: |
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#67 |
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Forum Member
Join Date: Sep 2001
Location: Manchester
Posts: 348
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They were running 16QAM until yesterday, I understand they're doing coverage tests on QPSK over the weekend with a view to moving over to it (and getting the necessary changes made to the NIT) until they can make the necessary improvements to the aerials, then they'll probably go back to 16QAM.
6Mbp/s is a little on the small side, but it's probably the most robust settings they can use without the payload getting much too small. I'd have thought running at 7/8 would be sailing fairly close to the wind. Up until yesterday Channel M was running at 9Mbp/s, the picture quality was pretty good. I'm not sure there's really a free reign regarding transmission parameters, I'm pretty sure the DTG only test a subset of modes on their zoo. Hence, I'm told, their initial reservations on using QPSK. |
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#68 |
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Forum Member
Join Date: Jun 2005
Location: Guildford / Crystal Palace
Posts: 13,114
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It certainly looks as though GMG/Channel M are waking up to the realities of local TV at last. They appear to be making all the correct engineering decisions. I wonder who advised them? It's just a shame that they had to destroy the once loyal audience they had on analogue.
Will we ever see Cube Interactive's Welsh local service from Wenvoe? |
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#69 |
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Forum Member
Join Date: Feb 2003
Posts: 1,256
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Quote:
They were running 16QAM until yesterday, I understand they're doing coverage tests on QPSK over the weekend with a view to moving over to it (and getting the necessary changes made to the NIT) until they can make the necessary improvements to the aerials, then they'll probably go back to 16QAM.
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#70 |
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Forum Member
Join Date: Sep 2001
Location: Manchester
Posts: 348
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We have trees at the end of our garden, and pre-DSO it was almost impossible to watch DTT during the summer months. Only once the power increased did it become less of an issue (unless it's windy, in which case I still get breakup). Bearing in mind these services were 10 kW, then I'm surprised I get the Channel M mux at all.
At the risk of derailing this technical discussion, the old channel M created some great content but was financially unsustainable, something needed to be done. But the way the chimps at MEN Media handled the two downsizing exercises was laughable. |
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#71 |
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Forum Member
Join Date: May 2002
Location: Beds (Sandy Heath TX)
Posts: 8,852
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Quote:
A QPSK FEC 1/2 mux only has a capacity of 6Mbps (or 2 SD channels) which explains why MANCHESTERLOVE has had to be removed to accommodate Movies4Men.
Canis are saying they still have space for more channels, so QPSK mode probably isn't going to last long. |
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#72 |
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Inactive Member
Join Date: Apr 2010
Posts: 884
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Quote:
The local Manchester mux used to be 16QAM IIRC but they seemed to have taken my advice to use QPSK for better coverage.
![]() A QPSK FEC 1/2 mux only has a capacity of 6Mbps (or 2 SD channels) which explains why MANCHESTERLOVE has had to be removed to accommodate Movies4Men. However they can change the FEC rate up to 7/8 to achieve a bitrate of 10.5Mbps on QPSK offering maybe 3 video streams and a few GMG radios. As soon as they need more capacity they will have to revert back to 16QAM with a slightly reduced footprint. The extra coverage achieved by sacrificing bandwidth will be considerable. In 16QAM mode the ch m mux keels over at-23db which from memory the -3db points on the antenna radiation pattern is +/- 20 deg . The planners seem to have tried this tactic of placing a local TV mux next to a PSB mux typically 20db higher. At the same time severe restriction on the radiation pattern imposed by the planners results in only QPSK providing reasonable coverage. This of course limits a local telly station ability to offer good coverage and offer spare capacity on the mux. This grubby bit of planning in my opinion has been deliberate, Because this magic figure of 1kw ERP and modulation of QPSK was proposed at a Ofcom meeting several years ago. I took the Arthingy planners to task on this issue at that meeting. It has been clear the planners intention from the get go was to place local TV muxes at -20db adjacent to high power muxes to compromise coverage. Fortunately Ofcom seem to have responded to this and put pressure on the planners. Ofcom have been great in putting a halt to this abuse and as such my respect for the individuals concerned at Ofcom is very high. |
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#73 |
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Forum Member
Join Date: May 2007
Location: Preston
Posts: 1,106
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Edit: nevermind....
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#74 |
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Forum Member
Join Date: May 2002
Location: Beds (Sandy Heath TX)
Posts: 8,852
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Any changes? M4M should have launched properly yesterday...
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#75 |
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Forum Member
Join Date: Feb 2003
Posts: 1,256
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I've not seen any changes - only Channel M is being broadcast, and the mux is still QPSK with FEC of 1/2.
edit: and we have no evidence that I know of that M4M was anything other than a placeholder or test feed. Time will tell if it was the actual channel that the earlier press release alluded to. You could even argue the opposite- the fact that it was taken down quickly once it was spotted could imply that in some way it wasn't supposed to be seen there in the first place. |
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