What has happened to the Manchester Mux? Since new channels were added last week I've not been able to receive a thing. Admittedly I only watched Movies 4 men occasionally when they had on laurel and hardy or the occasional classic costume drama and channel M for its archive of programmes I couldn't see the first time because of not being able to receive it in the past. can't be received on external aerial or indoor arial as it could before - not even an email address to ask them directly.

Previously, it was broadcasting on the very robust QPSK mode - this means that even if the signal is very poor quality, the receiver can still get enough data to decode it, as there's a lot of redundancy (error correction codes, etc.)


However, that mode does have its drawbacks - the main one being that only two channels can fit onto it (with the mode they were using, at least). So, GMG (the owners of the mux) decided to change the mode to QAM16 - this is what some muxes (Mux 1, Mux B, Mux C and Mux D) are/were running pre-DSO, and as such is reasonably robust, but not nearly as robust as QPSK. We all expected them to either increase the power or the aerial height, or both, with the change (as the frequency they are using was previously in use nearby, but now isn't), but that didn't appear to happen, so the net effect is that many people who could receive it before now can't.


I would expect them to either change back to QPSK and get rid of the extra channels, or increase aerial height and/or transmission power some time soon, else they should expect to lose even more customers.

I live in Central Manchester in a tall building with an aerial on the roof, and I can no longer receive the MUX, and if I can't probably very few others can either.

I reported this on the Movies4Men website. They said they would get back in 48 hrs but have not done so.

Channel M does not have a website any more, and I cannot find any contact details for them anywhere.

They're owned by GMG (Guardian Media Group - the same people who own the Guardian newspaper), if that's any help with you contacting them.

OK Thanks, I now have a number for them. I'll try ringing tomorrow.

So basicly we're buggered by them trying to get too many channels into too small a space on too low power it seems

Basically - Yes

It's usually a compromise between quality and quantity, and they generally prefer quantity. Except this time they seem to have shot themselves in the foot.

They did that when they closed a perfectly healthy analogue local TV channel and lost their audience by not starting up in digital for months. How many feet have GMG got?

Thanks for all your messages on this - it's always nice to learn something new

City centre coverage has always been sketchy given the building clutter and low power of the mux. Less built up areas around (and particularly north of) the city centre fare a lot better.

Looking at the maps on pages 19 & 22 of http://stakeholders.ofcom.org.uk/bin...tice524/im.pdf it looks like the city centre lies on the edge of the area that can receive a QAM signal. So it is perhaps not that surprising that some of us have lost it.

Figures in the document suggest a 40% drop in coverage by going from QPSK to 64QAM. (It has actually only gone to 16QAM, so probably about 20% loss)

Anyway I rang them (0161 886 8800) this morning and the woman said she would inform an engineer of my complaint but no reply as yet.

I've started getting picture breakups on these channels since yesterday. I have therefore deleted them from my EPG.

I'm very surprised you managed to pick anything up at all given you're in Chorley.

Also, the mode change was last week, so I doubt it has anything to do with it, since you only starting experiencing problems yesterday.

I have been able to pick them up in Southport. Not 100% perfect and with some breakup but watchable.

I've not tried since this change, will give it a go tonight,

Yes, I used to receive Channel M and the Movies4Men channel without any breakup (3/4 signal). I guess that's because I have line of sight to WH. I realise that the changes were made last week (perhaps I was lucky with the conditions for the first few days) but now I get constant break-ups which must be related.

Had solid Channel M coverage in Cheadle previously. Since the change there is regular break up making all the local Muc channels unwatchable. GMG are obviously going to find the consequences of their actions the hard way - wonder if Movies 4 Men have a break clause if coverage is not delivered?

That's incredible, unlike the other services on Winter Hill, the Channel M signal is highly directional. In fact, it's almost 180 degrees away from Chorley (as it's pointed at Manchester). Combined with the low power, I'm absolutely amazed you ever got anything.

The only way to accurately gauge coverage would be to do a field survey of the area. A few posts on a forum is hardly the same. Success is likely to be gauged on BARB results, if the handful of BARB households in Manchester still get it, then there isn't an issue.

mb21 has published pictures of the Winter Hill mast taken in November 2011 and it can be seen that the Channel M antenna has not changed in any way.

http://tx.mb21.co.uk/gallery/gallery...71&pageid=1005

There certainly seems to be adequate space for it to be raised. I guess GMG can't afford Arqiva's fees.

mb21 has published pictures of the Winter Hill mast taken in November 2011 and it can be seen that the Channel M antenna has not changed in any way.

http://tx.mb21.co.uk/gallery/gallery...71&pageid=1005

There certainly seems to be adequate space for it to be raised. In case mb21 was wrong about the Channel M antenna, I looked in vain for any UHF antenna half way up the mast. There is no sign of any UHF antenna.

Looking through the archive, it seems that the Channel M antenna is just over halfway up the first section which is 100 feet to the first observation platform; so it's about 60ft up the mast, which is about 1000 ft high.

The Arqiva planning documents for coverage envisioned the Channel M antenna being 140m high which is about 500ft or half way up the mast. Even the reference offer states that the antenna would be mounted at the 140m level.

So it's no wonder the signal is weak. I guess GMG can't afford Arqiva's fees. Or GMG is incompetant. Again.

Increasing the height of the aerials alone will not make a weak signal strong. Nor will it do much to increase coverage, the height of the site above sea level means you only really need to clear the immediate area, which it does. An increase in power is what's required, but that would not only require money (which, given the current programming, it's painfully obvious it's something they have very little of) but also signoff from Ofcom, which they might not get.

While we're on the subject of incompetence, you're in danger of being a bit of a hypocrite.

Hmm you are always defending GMG. I wonder why? Perhaps you are partly responsible for their self inflicted disaster.

Height is essential to get into urban areas like Manchester, not just for landscape topography but to clear tall buildings. If you read the Arqiva planning document for the new proposed local TV, you will see that they require antennas half way up most masts to achieve the required penetration.

If we take the example of Winter Hill, that apparently will supply another Manchester service on UHF56 using 1kW ERP with an antenna half way up the mast (approx 500ft). Arqiva state that QPSK with FEC 2/3 is essential to provide a robust signal in the presence of high power DTT. So assuming Channel M went back to QPSK with its 50ft antenna, ten times lower, using the same 1kW ERP, do you really think the coverage of the two muxes would be the same? Of course it wouldn't, both height and power affect the coverage area.

The ERP and height are GMG's first problem but its main incompetence is using the 16QAM mode instead of QPSK which also reduces coverage as evidenced by posts in this forum.

Spouting personal insults will not change the facts that you apparently disagree with. I can't think of a broadcaster more inept than Channel M and its management at GMG.

Or perhaps I'm just sick and tired of your continual bashing of them. Your tone is always one of derision, that you could do 'so' much better yourself. Is it any wonder why many people just write you off as an armchair critic without any real insight into the way these businesses work? You also rarely enter these discussions from a neutral standpoint, you always seem to have an axe to grind, and that, quite frankly, gets a little tiring. I'm sure they don't do things like they used to 'in the old days', but that's all in the past, and no amount of flaming on forums will change that.


Height has almost nothing to do with it, the site itself is more than high enough to give acceptable results. If they moved further up the mast, you might see an improvement in some fringe areas (particularly the areas in the shadow of the hill itself). But the only thing to get past the building clutter in the city centre is more power. Moving to QPSK doesn't yield enough usable bandwidth if you want more than two services.


I was merely pointing out that if you're going to call someone out on the subject of competence, you could at least spell 'incompetence' correctly. Basic stuff really.

Well you're going to get really fed up because if Channel M keep doing foolish things, or fail to correct their existing mistakes, I will keep on pointing it out. I don't believe that large companies with all the resources available to them like GMG should be immune from criticism just because you have some kind of relationship with Channel M which you are not prepared to reveal.

When posters start criticising your spelling, it is fairly certain that they are not really interested in technical arguments. In fact I first suggested in this forum that Channel M should use QPSK and congratulated it when it did.

Again you say "height has almost nothing to do with it". This is simply wrong. Antenna height is not just important because of the actual height above sea level, but because the receiving aerials will be aligned on the main DTT antenna at the top of the mast and not necessarily the weaker one at the bottom. The top is of course the optimum location for the placement of the Channel M antenna. Co-location is fairly essential where you are trying to receive a 100kW DTT signal along with a 1kW local TV signal. Half way up the mast is, I suspect, an Arqiva suggested compromise to limit cost but get some signal strength into receiving aerials. Many posters will be aware of severe degradation at some receiving sites when DTT is switched from the main antenna to reserve antennas slightly lower down the mast. So I say again that placing the Channel M transmitting antenna at 50 ft up a 1000ft mast is seriously wrong unless you expect every household in the fringe area to realign and/or upgrade its aerial. In this instance Channel M is not acting as a sole broadcaster but as part of the whole DTT system.

Now you say that "Moving to QPSK doesn't yield enough usable bandwidth if you want more than two services." Well I am sorry, you can't just pluck a random figure out of the air and say that I am going to broadcast "any number" of services at 1kW ERP. The local TV service uses interleaved spectrum and so power levels have been based on a maximum of 10kW ERP or what is required to cover the target area using QPSK, in this case Manchester City centre, whatever is the minimum. Three TV channels is about it for local TV.

If for example the Channel M ERP was raised to 10kW, then interference might be experienced on the main users of UHF57 elsewhere. On this point I tend to agree with Arqiva, that QPSK FEC 2/3 is the correct mode to use for local TV. Using more complex modes will reduce coverage over the planned arrangement. Using QPSK will reduce any interference into main DTT by virtue of the different mode as well. If it is physically possible to raise the ERP to 10kW without adverse effect, then I am all in favour. But I suspect that planning based on a 500 ft antenna instead of a 50 ft one limited ERP to 1kW.

So really how can you justify Channel M's decision to use 16QAM with the same power and antenna characteristics as it formerly used with QPSK? It is bonkers.

Having now considered DCMS & Arqiva proposals for local TV, I tend to agree with the basic principal that QPSK should be used with a maximum of three TV channels on the interleaved spectrum. One is handed over to the local TV companies FOC and the other two are handed over to Arqiva to pay for the engineering infrastructure. At least that way there won't be any crazy TV company ruining its coverage by making technically incorrect decisions. I am quite a fan of local TV and I hope that it all works out. Letting the local TV companies operate their own transmitters is going to cause trouble and maybe the Channel M experiment has helped in this regard.

With the greatest respect Ray you are technically incorrect.

The real cause of the problem for channel M coverage is the very low power of 1 kW ERP to a adjacent channel of 100kW , plus the extremely restrictive broadcast antenna template which is much more severe than the restriction template.

By the way the restriction template was mysteriously it seems kept from channel M until after they were on air

Had this been available at the time, much improved coverage could have been achieved towards the east of Manchester from the get go.

This in effect forces channel M to use QPSK modulation because 16QAM will keel over if the adjacent channel is -23dB or lower

This only provides a margin of only 3dB .

Then if you look at the antenna template strictly imposed on channel M by the planners you will see at only +/- a few degrees it reaches the -23dB threshold.

The so called relaxation after DSO at Wrekin is in fact smoke and mirrors because the restriction towards Biddulph relay prevents further improved coverage towards the South of Manchester .

The mere fact that only three houses are affected by possibly interference from the channel M transmitter in the Biddulph area and also the fact they are using Winter Hill as there main terrestrial transmitter source as is a very large percentage of those previously using the Biddulph relay ,seems not to have been noticed by the planners.

You mentioned height as a cause of the problem , or channel M not taking advantage of moving the TX antenna higher up the mast at Winter Hill.

There is no advantage whatsoever of doing this as the site height is 440m approx and city Centre Manchester is approx 50m high above sea level.

The major physical restrictions in the area are the Pennines towards Yorkshire.

Leaving the antennas at there present height in my opinion is the correct thing to do as this should allow a relaxation of the restriction template.

Since when was Arqiva the one who decides if a local TV station should broadcast at QPSK ,16QAM or 256QAM using DVB-T2 which would carry 15 or more SD programs.

This is for Ofcom to decide?

Also why should Arqiva be allowed to operate local telly muxes which further increases their stranglehold on the market?.

Channel M have operated their analogue and digital transmitters with great skill under very difficult economic times.

Ray you clearly wish to promote monopolies with your comments?