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Old 28-04-2011, 23:08
a516
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High profile! Ha! I'd like to see how this regional trial goes. I can't see people dying to see this channel...

But thanks for letting us know first.
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Old 28-04-2011, 23:39
Greebo
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Greebo make sure you post in the Changelog.
I'll do that once we have something concrete rather than just a hidden test stream. In fact I just rescanned and it has mysteriously vanished:

PID found: 0 (0x0000) [SECTION: Program Association Table (PAT)]
PID found: 16 (0x0010) [SECTION: Network Information Table (NIT) - actual network]
PID found: 17 (0x0011) [SECTION: Service Description Table (SDT) - other transport stream]
PID found: 18 (0x0012) [SECTION: Event Information Table (EIT) - other transport stream, schedule]
PID found: 20 (0x0014) [SECTION: Time Date Table (TDT)]
PID found: 32 (0x0020) [PS/PES: ITU-T Rec. H.262 | ISO/IEC 13818-2 or ISO/IEC 11172-2 video stream]
PID found: 33 (0x0021) [PS/PES: ISO/IEC 13818-3 or ISO/IEC 11172-3 audio stream]
PID found: 38 (0x0026) [unknown]
PID found: 257 (0x0101) [SECTION: Program Map Table (PMT)]
PID found: 8191 (0x1fff) [stuffing]
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Old 28-04-2011, 23:59
Ray Cathode
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Your PID 38 will be either subtitles or audio description for Channel M
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Old 29-04-2011, 00:15
chrisy
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High profile! Ha! I'd like to see how this regional trial goes. I can't see people dying to see this channel...
High profile might have been stretching the truth a bit, but it is relatively well known (at least on here I've seen it mentioned a lot, usually in threads like the Ch45 one), and it isn't tat like shopping or religious nutters.

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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Old 29-04-2011, 00:33
marria01
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Your PID 38 will be either subtitles or audio description for Channel M
It's the PCR for 28673 (Channel M).
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Old 29-04-2011, 00:46
marria01
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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
Interesting, shows up as QPSK 1/2 1/32 here.
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Old 29-04-2011, 01:54
Ray Cathode
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It's the PCR for 28673 (Channel M).
Normally the PCR uses the video PID.
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Old 29-04-2011, 08:28
Greebo
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Interesting, shows up as QPSK 1/2 1/32 here.
Confirmed here as well, once locked to the mux, dvbsnoop -i feinfo gives:
Stream code rate (hi prio): FEC 1/2
Stream code rate (lo prio): FEC 1/2
I 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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Old 29-04-2011, 08:38
Greebo
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It's the PCR for 28673 (Channel M).
Normally the PCR uses the video PID.
I think you are both right. Decoding the PMT on 257, it clearly shows that the PCR is 38:
------------------------------------------------------------
SECT-Packet: 00000049 PID: 257 (0x0101), Length: 52 (0x0034)
Time received: Fri 2011-04-29 08:30:15.668
------------------------------------------------------------
PID: 257 (0x0101)

Guess table from table id...
PMT-decoding....
Table_ID: 2 (0x02) [= Program Map Table (PMT)]
section_syntax_indicator: 1 (0x01)
(fixed '0'): 0 (0x00)
reserved_1: 3 (0x03)
Section_length: 49 (0x0031)
Program_number: 28673 (0x7001)
reserved_2: 3 (0x03)
Version_number: 3 (0x03)
current_next_indicator: 1 (0x01) [= valid now]
Section_number: 0 (0x00)
Last_Section_number: 0 (0x00)
reserved_3: 7 (0x07)
PCR PID: 38 (0x0026)
reserved_4: 15 (0x0f)
Program_info_length: 17 (0x0011)
So this mux does that differently to the other 6.
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Old 29-04-2011, 11:27
marria01
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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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Old 29-04-2011, 12:17
omnidirectional
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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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Old 29-04-2011, 12:26
Ray Cathode
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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?
The clash was with a 16QAM COM mux which does not move until September so no change to Channel M until then and maybe a reason why they are using QPSK mode.
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Old 29-04-2011, 12:30
Ray Cathode
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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.
The only users of separate PiDs for Video & PCR on DTT are some of the Mheg protected adult channels.
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Old 29-04-2011, 12:50
marria01
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The only users of separate PiDs for Video & PCR on DTT are some of the Mheg protected adult channels.
So no problems then.
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Old 29-04-2011, 12:51
Ray Cathode
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Interesting, shows up as QPSK 1/2 1/32 here.
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.
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Old 29-04-2011, 14:04
Greebo
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I have no idea where the linuxtv_dvb_apps scan command gets the extra 3_4 from.
Progress... if you look inside the NIT broadcast on any of the SD muxes from Winter Hill, the local mux is being advertised as QAM16 with FEC 1/2 and 3/4 - so that could well be where the linuxtv_dvb_app scan is getting the wrong info from.

Transport_stream_ID: 28672 (0x7000)
Original_network_ID: 9018 (0x233a) [= UK Digital Terrestrial Television | Independent Television Commission]
reserved_1: 15 (0x0f)
Transport_descriptor_length: 30 (0x001e)

DVB-DescriptorTag: 65 (0x41) [= service_list_descriptor]
descriptor_length: 3 (0x03)
service_ID: 28673 (0x7001)[ --> refers to PMT program_number]
service_type: 1 (0x01) [= digital television service]


DVB-DescriptorTag: 90 (0x5a) [= terrestrial_delivery_system_descriptor]
descriptor_length: 11 (0x0b)
Center frequency: 0x048ab840 (= 762000.000 kHz)
Bandwidth: 0 (0x00) [= 8 MHz]
priority: 1 (0x01) [= HP (high priority) or Non-hierarch.]
Time_Slicing_indicator: 1 (0x01) [= Time Slicing is not used.)]
MPE-FEC_indicator: 1 (0x01) [= MPE-FEC is not used.)]
reserved_1: 3 (0x03)
Constellation: 1 (0x01) [= 16-QAM]
Hierarchy information: 0 (0x00) [= non-hierarchical (native interleaver)]
Code_rate_HP_stream: 2 (0x02) [= 3/4]
Code_rate_LP_stream: 0 (0x00) [= 1/2]

Guard_interval: 0 (0x00) [= 1/32]
Transmission_mode: 1 (0x01) [= 8k mode]
Other_frequency_flag: 0 (0x00)
reserved_2: 4294967295 (0xffffffff)

then as actually locked by the tv card:
Current parameters:
Frequency: 762000.000 kHz
Inversion: OFF
Bandwidth: 8 MHz
Stream code rate (hi prio): FEC 1/2
Stream code rate (lo prio): FEC 1/2
Modulation: QPSK

Transmission mode: 8k mode
Guard interval: 1/32
Hierarchy: none
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Old 29-04-2011, 14:24
marria01
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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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Old 29-04-2011, 14:45
Ray Cathode
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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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Old 29-04-2011, 14:47
Greebo
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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.
I really hope they do stick with QPSK for now. From early April my pc card hasn't been able to lock onto the mux - until 6pm yesterday when it burst back into life. I'm assuming nothing changed in the transmission to degrade anything so was blaming the trees coming into leaf and my lazy loft aerial setup due to Winter Hill being so powerful here.
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Old 29-04-2011, 16:11
marria01
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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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Old 29-04-2011, 16:53
chrisy
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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.
MANCHESTERLOVE could have been converted to an MHEG service. (I'm assuming it was bringing in some cash)

Canis are saying they still have space for more channels, so QPSK mode probably isn't going to last long.
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Old 29-04-2011, 21:50
plane spotter
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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.
It makes sense to optimise coverage as ch 58 is a PSP mux 20db higher.
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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Old 30-04-2011, 09:37
Furnell
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Edit: nevermind....
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Old 02-05-2011, 14:15
chrisy
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Any changes? M4M should have launched properly yesterday...
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Old 02-05-2011, 14:24
Greebo
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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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