I totally agree that CCI will be a problem if a margin for lift isn't applied in the planning and the same polarisation is used .
There shouldn’t be any CCI at all in the UK as the several makes of propagation software provides the function to calculate and make allowance for lift.
The only areas were there should be and I believe is CCI is around Southampton and along the coast because of interference from French stations .
The solution to this is to use lower power transmitters in a more robust modulation method and a few more of them and use greater bandwidth. IE more channels.
These transmitters need to be inland so the antennas can take advantage of the 20dB or so front to back ratio because they are pointing in the opposit direction from France
What we have in fact is a main transmitter at Rowridge on the Isle of white with the local TV rooftop antennas pointing out to sea towards France.

So using a more robust modulation method and having most coastal RX antennas pointing inland instead of out to sea adds a extra 26-30dB margin .

Just to remind you there is almost 30dB difference if 64QAM or 256QAM DVB-T2 is used comparing digital to analogue CCI thresholds without using single frequency networks.
A extra 10dB or so protection ratio can be added by using a reduced capacity modulation method such as 16QAM.
So this adds that much immunity that it allows many frequencies to be used to compensate for the reduction in bit rate.
As I said the planners need a little help bless em.

It's too late now: the transmitters are where they are now with 50 million aerials pointing at them.

As I told planespotter our UK TX arrangement was formed for VHF Bands I & III with dual UHF operations later. It may not be ideal now but it's the only one we've got. There is no prospect of major change.

Ah, that's an older consultation. Still interesting, but quite a lot of stuff from people wanting to run the "backbone" which no longer exists.

The point I was trying to make was that analogue is much more prone to CCI than digital as most on this forum are only to aware.
If we can operate 5 national analogue stations digital in comparison is very easy to plan for especially with the software we have know what wasn’t available to those brilliant planning engineers at the beeb and IBA when UHF was first rolled out.

Even at Rowridge after DSO there shouldn’t be any CCI problems at all around the Southampton area if the correct engineering is applied.

A deeper issue seems to be prevailing here.

In the past engineers like myself originated as HAM radio enthusiasts and lived and breathed the technology when we were just out of nappies.
Many of us got jobs in this industry .
What is apparent know is the current intake of engineers have not come from this background ,but have a piece of paper from university that says they are all knowledgeable and skilful.

In addition many haven’t worked up from the bottom and actually done the job. I run across this all the time in many other countries and all the same problems are apparent.

This lack of skill is not just apparent in telly broadcast but it prevails big time in the cellular coverage in the UK and other countries.

Anyhow this is drifting of topic ,but what is needed is a big intake of engineering know how to make local telly work in the available spectrum and whatever the programming content if coverage sucks through poor engineering local telly will flop again.

We never got full coverage of the fifth channel, though. We could easily get decent digital coverage if we went from five MUXs to 4- by getting rid of the porn and shopping- leaving more space for local channels.

this sounds like another world - not the one we live in. Esp the bit about most relays not being needed - I bet infact most are needed, with a minority being installed in the analogue days to cure ghosting issues.

At this location, our line of sight is only just and just blocked by a single hill to the main mast (i researched it on a web site showing a straight line with terrain on it), yet despite this and the fact we had a massive aerial with a booster reception post switchover was no good. I know from other locations that their line of sight to a main mast is far more blocked than ours, so in most cases those locations really do need a relay mast to provide a service.

I am not saying that all relays are not needed but some that are marginal are not needed now..

Direct line of sight is not needed for RF propagation .

OFDM or COFDM as it is known for telly purposes is a brilliant bit of technology that allows for example mobile phones to work inside moving cars .

Its specific design addresses one of the major obstacles in broadcasting using digital technology by using COFDM modulation.

Were there is no multipath issues COFDM isn’t used such as in satellite broadcasts as a proportional part of the bandwidth is dedicated to antighost or multipath issues so this sacrifices payload..

Satellite broadcasts has to be more efficient on S/N rather than anti multipath so COFDM isn’t used as anti ghosting is not needed so this releases more bandwidth.

Path loss at 700MHz for 70 miles is 130 dB

For 22,000 miles at 12Ghz it is 205dB

So you can see from these path loss figures S/N is the issue with sat broadcasts and power levels can be exchanged for improved antighost with terrestrial TV broadcasts.

Read the following from the beeb .

a really good source of tecky info

http://downloads.bbc.co.uk/rd/pubs/p..._278-stott.pdf

If there is no terrain impediment all that is needed for a digital transmitter with a suitable broadcast antenna with 10db of gain to broadcast 70 miles at 700MHz is a 100 watt transmitter with 10dB of overall antenna gain.
But add a sufficient fade margin a word used more in microwave propagation but applies here except the fade is terrain and other obstructions more than rain .

The power is then lifted up by 30dB to 100kW. This provides a 30dB margin at 70 miles ,plus a extra 5dB or so can be added with a high gain antenna as the planning assumes a 10dB gain rooftop antenna.

In addition depending on the download losses and tuner performance a pre amp will add another 6dB in threshold (not gain),
So the overall margin for broadcast after DSO for the PSB broadcasts is about 40dB plus , a 10,000 to 1 ratio.

Refraction loss due to terrain in most valleys is often not greater than 40dB. Unless you get a mixture of forests and hills as obstruction, consequently COFDM modulation can cope with this if there is sufficient fade margin due to adequate transmitter power.
Analogue when encountering a 40dB of refraction loss would have severe ghosting.

And your point is?

... Digital is better than analogue?

We know that

the line i have put in bold is quite misleading - the suggestion being that if you dont have line of sight to a main mast, you can still get a signal - every time, which is not the case. In some examples you maybe lucky, but in many cases you wont be - the reception maybe variable too - depending on weather, time of year, or extra things such as tree's. I just wont people spending loads of money of massive aerials to get main mast reception (rather than FVLite on a nearby relay mast) only to later discover that it goes through periods of poor reception. People should at least be aware of the *risk* involved and they can make up their own minds.

No it is not,

Well it could be, but it is not because too many channels are squeezed in and compressed far too much, even the so called HD channels are not much better.

I think Ray meant "as a broadcast medium".

What people stuff into the transport stream might be crap, but you can't deny that it is easier to receive a perfect digital signal than it is an analogue one.

If you used it to broadcast one TV channel per 8MHz channel (ie. a direct replacement for analogue), then it would be obvious which is better in all respects.

Even four HD channels in one multiplex - taking the same space as one analogue channel - are so much superior, in picture quality, functionality (EPG, AD, etc), and ease of reception, that arguing otherwise is pointless.

Anyway, this is off topic.

In some instances if the changes in weather and other variables push the signal past the cliff edge and of course this isn’t acceptable and a relay is needed.

But even with a simple 10dB gain rooftop yagi reception in areas that previously suffered ghosting and poor signals and needed a relay, now some will get perfect reception given the right criteria such as the big increase in ERP during so called DSO as long as the variables do not bring reception past the cliff edge..

Digital broadcasts of course will not result in no relays being needed but lots of viewers are getting good reception from the main transmitters that previously didn’t in particularly were the power of the transmission has been increased.

A power of 100kW ERP digital is similar to 20 MW ERP of analogue ,at the very least depending what yardstick is applied with regards to receiver S/N .

There was little point in wacking the power up too much with an analogue TX as past a certain point were the terrain impedes signal ,nothing is gained as multipath is too severe..

This point is much further along with COFDM so a big power increase to overcome terrain impediments achieves more.

indeed. A digital signal can provide perfect sound and vision without being 100% strength. With regard to not all relays being needed - yes this is also true due that effect, but it then requires people to have either their aerials realigned or new aerials too - and I dont know how many would be prepared to do this, with the option of free this and free that offers from Sky.

Ofcom consultation on licence award process etc:
http://stakeholders.ofcom.org.uk/con...ions/local-tv/

Only real new bit of information is that DVB-T QPSK is proposed (although Ofcom are considering DVB-T2 QPSK too) and they are going to do some testing to check the compatiblity of this mode with existing receivers.

Does anybody know why QPSK is being insisted on .

Surely it should be up to the Mux Owner to decide the trade off between how many TV programs can be carried in the mux and the coverage.?

QPSK is not the answer in many locations with regards to coverage.

Or is this Ofcoms policy to protect Arqiva?

I assume it is to ensure best possible coverage for the local TV operator.

Low power DVB-T needs to use QPSK in the presence of high power DTT to keep an adequate margin. Otherwise we get a Channel M situation where you proved that 16QAM 1kW muxes in the presence of 100kW 64QAM muxes will disappear into the background noise with today's receivers.

Coverage is limited by the use of interleaved spectrum which in turn requires low ERPs.

By getting Arqiva to agree to QPSK, that restricts their own quasi-national channels to a maximum of 2.

I think that DVB-T2 would allow more channels per low power mux. However the local TV Co would only get 1 channel in any case.

If DVB-T2 was used, the local channel company could have their local TV channel, a HD simulcast and a +1 version (the +1 version would supposedly bring in more advertising revenue).

Not that simple.

The channel M situation was and is a 100kW ERP channel 58 next door to channel M’s 1kw ERP channel 57 (couldn’t have picked a worse combination).

The keel over point with 16QAM of course is about -23dB ,so this leaves a 3dB margin.

Add to this the extremely narrow radiation pattern that Arqiva planning proposed and was implemented results in the ERP reducing by 3dB at +/- 15 degrees the keeling over point for 16QAM.

So any coverage past +/- 15 degrees doesn’t work or is unlikely to work if 16QAM is used.

Yet the restriction template was mysteriously not included in the original licence document . Hmmm I wonder why, it must have been inadvertently forgotten ?

The restriction template that appeared later clearly allows a very much better coverage even before DSO at the Wrekin and it is relatively simple for an experienced engineer to configure the broadcast antenna radiation pattern to better fit within the restriction template so that improvements to the coverage in around Manchester could have been made with full compliance to the restriction template published by Ofcom .

This apart from making a big improvement in coverage this would allow 16QAM to be used . The keel over points at -3dB would allow +/- 35 degrees of coverage at 16QAM .

You are correct about local telly getting one channel ,but this doesnt apply to ch M.
PS
Ray I value your input and happy Christmas to you.

But that was never proposed. Any additional channels would be for MuxCo to sell.

It's nice to note that QSPK is the preferred mode, as Ofcom must surely know that for Local TV to succeed, it needs the maximum coverage it can get. The two extra channels are a happy by-product which can help the multiplex be profitable and self-sustaining.

If it was upto the Mux owner to determine mode, you would get e.g. Arqiva or whoever is the mux owner changing the mode at the detriment to the local TV service coverage to make a few extra £s and end up with a Channel M situation, where coverage is not ideal. It almost looks like the other proposed local mux for Manchester will have a better coverage than Channel M's.

I was referring to the new proposals, except to say why local TV Cos should not be allowed to make their own technical arrangements using Channel M as an example.

Surely even you would agree that planning a broadcast service using DTT with a 3dB margin is stupid. Variations in propagation due to weather, tropo effects and local interference would make such a service margin totally insufficient never mind the sector angle you quoted. I just hope no one does an actual reception survey of Channel M. If they do I fear the Dolphin TV suite of channels will go away.

When will Channel M recognise the realities of their situation? QPSK is the only possibility with the present arrangement. And a better antenna would help.

What are ofcom doing in giving space for some local channels, when DSO has not finished yet and there is down turn in advert money at this time for our national channels, so were is the funds for these new channels going to come from as the BBC is cutting so many shows next year that it will be like UKTV channels on four hour repeat system and ITV lost with bad managerment that damage the Royal mail. And Channel Five that has no money to have it's HD channel on freeview with the high cost of space on freeview.

So do we really have such mad people at ofcom to think at these times and with selling off space from the DSO to phone companies that freeview can have such a mess with some areas of the UK having extra channels and others non ...... IS that a really fair national public TV system that the UK needs ? where some richer places for local adverts and viewers to have channels and others do not on "Freeview"

So Ofcom whats a multi channel system that if you are rich and live in large towns you can have all channels that can be on a mux and if you outside a town and can not have paid for sports etc.you will have less channels and outer town you will have less speed on your internet service so you are not going to be able to use Iplayers or IPTV systems too. FAIR ?????

Freeview & FreeSat should have all the space for TV companies to join at a cheap rate with out bidding races at high cost and all channels to be fully national over the UK .

We need any money in the TV world to be put to the channels we have now for good shows and less repeats.

I agree planning for a 3dB margin is stupid ,but what I was suggesting with regards to improving the antenna radiation pattern would make a huge improvement to the existing set up especially if QPSK were to be used.

Lets be frank the very narrow antenna radiation pattern imposed on ch M sucks.

A major improvement that could resolve the issue with regards to using 16QAM is to provide an extra 6dB of margin by increasing the ERP to 4kW .

An increase in ERP would help resolve some of the city clutter problems in central Manchester

This I believe can be done while retaining the protection ratios required with other close by broadcasts on the same frequency.

A further 2db ish margin can be added by adopting 1/2 code rate at 16QAM if there were no compatibility or nit issues ,this of course reduces capacity.


What is going on here is potential local TV broadcasters want control of there own mux like ch M and use any spare capacity to lease to others to subsidise the station .

Nothing wrong with that?.

But this creates a potential competitor for Arqiva and it is only natural they do not want that and you cannot blame them .

I believe the concept of MuxCo was created to prevent local telly stations from competing against Arqiva , but that is just my opinion.
If Arqiva become MuxCo this will be anti competitive and in my view warrant a very strong representation to the Competition Commission.
Arqiva,s argument they originally put forward to enable them to become a monopoly was the economies that would be achieved would be passed on to the broadcasters.

The government of the day were naive to believe this.

It is clear that this has not happened and what we have is the potential abuse of monopoly power now allowing a proposed MuxCo that is not even necessary that probably will pass into Arqivas hands and will further cement their monopoly .

Never in history has a monopoly benefitted the customer !.

Check your fact and figures - the above is not valid.

Lars