Blank TV screens as cable firm ditches analogue

In article ,
says...

The SAW filters in analogue TV modulators and translators were a minty
bit dearer than those used in STBs (typically £80). However, even these
were not sufficiently 'brick wall', and required a helping hand from
additional tuned traps on the adjacent sound and vision carrier
frequencies. Further out, the rejection of the filter itself tended to
be limited to maybe 50dB, but usually other bandpass tuned circuits
cleaned things up well off-channel. The overall result was that
throughput of the translator had unwanted out-of channel peaks at around
vision minus 3.5MHz and sound plus 3.5MHz. Because of the spectral
content of an adjacent analogue signal (which has most of its sideband
power density close-in to the carrier frequencies), this was sufficient
to ensure no real impairment to the wanted signal. However, when an
adjacent 8MHz band of constant-density digital signal appeared on the
scene, the performance was not quite good enough, and, either side of
the wanted analogue signal, two bumps of digital 'noise' got fed into
the cable network.

Hence the need for additional L-C traps for adjacent sound.


Interesting ... could this effect be vendor dependent?

My part of VM was what previously was Bell CableMedia, then Cable and
Wireless but the DTV roll out started out in the NW, previously NYNEX
territory.

There had never been any problems in The NW as far as I know, and the
first troubles occurred when the roll out extended south (and, I'm
certain, started in the midst of a large roll out exercise in
London/SE).

I'm not sure what HE equipment NYNEX used but ours was Scientific
Atlanta. I'm certain, though, that until the Crystal Palace DTT
transmissions started, we had no problems.


An upper adjacent digital does tend to overlap the NICAM of an analogue.
However, the digital signal is not the full 8MHz wide. It is about 7MHz
'across the top', and has to be well down towards the noise at 8MHz
wide. Also (although I haven't checked) I suspect that an upper adjacent
digital is offset HF (167kHz, isn't it?). If this was not done, I can't
see how (for example) Crystal Palace carries Ch33 analogue and Ch34
digital.


Ch34 HF offset? Yes.
http://www.ofcom.org.uk/static/recep..._guide_4_1.pdf

Yes. I'm sure you've already seen my reply to Bill's post, so I won't
repeat it here

snip


Obviously, additional rejection was required, and the most effective
(and foolproof) way of achieving this was to replace the existing
analogue processors/translators with a demod-remod system. NICAM was
provided either by a demod + re-encode/remod or (in at least one
network) taking it from the demodulator as a subcarrier at 6.552MHz, and
up-converting it the remodulator. Needless to say, none of this
re-engineering was cheap. Also, in order to accommodate the additional
equipment, there was often the problem of finding the additional space
in the already-crowded headend racks.

No argument there!

Well, I don't know. You could well be right. But the crux of the matter
is that the TV channel translators suddenly started causing problems on
the cable network because they lacked adequate selectivity in the middle
of the adjacent channels. This allowed bits of off-air digital 'noise'
to pass through, and get launched onto the cable network. It might have
gone unnoticed if the frequencies had been occupied by analogue signals,
but it definitely affected digital signals. The only practical cure was
the better overall filtering inherent in a demod-remod.

Again, I don't recall problems in the centre of the channels but the
'burst' of DTT signal at the bottom end of the channel could be very
clearly seen if the local DTV signal was removed - but then, problem
found, so i don't suppose there was any need to look further along the
channel!

--

Terry

Terry Casey wrote:
In article ,
lid says...
Andy Burns wrote:
On 15/12/09 19:07, Mark Carver wrote:

tim.... wrote:

Why didn't they overlay a message in the broadcast channel that the
service was closing. Surely they have the capacity to do this?
Unlikely, unless they demod the signal to baseband, which would then
require using expensive NICAM coders to restore those carriers.
Given they were going to ditch the channels all together, losing NICAM a
few weeks earlier to allow a warning caption wouldn't be such a loss.
No, but it's all effort and expense, something UK cable cos are not exactly
renowned for ! Let's face it, even our (so called) world class broadcasters
seem to have had a rather casual attitude to on-screen warnings in DSO areas
so far ?

As far as Virgin Media are concerned, this is an exception to the rule.
As I explained in another post, usually ALL subscribers receive the
service using a Set Top Box and VM know where all the old analogue boxes
are. All they need to do is to swap out all the analogue boxes for
digital ones. Once the last customer has been migrated, it is safe to
turn off the analogue service.

They may not have done. Remember when the analogue mobile phone networks
were turned off - the operators then said they knew some people were
still using them but couldn't precisely know who.


--

I'm not apathetic... I just don't give a sh** anymore

?John Wright

On Tue, 15 Dec 2009 09:28:04 +0000, chunkyoldcortina wrote:
But residents aren't happy cos the publicity has been that Digital
Switchover happens in that area in 2011 (the Sandy Heath switchover) so
"how dare Virgin switch it off earlier than the official date"
(paraphrased).

What does the "Digital Switchover" have to do with cable TV anyway? My
understanding was that it was solely about the terrestrial broadcasts
(i.e. what people receive through an aerial).

In article ,
Duncan Corps wrote:
On Tue, 15 Dec 2009 09:28:04 +0000, chunkyoldcortina wrote:
But residents aren't happy cos the publicity has been that Digital
Switchover happens in that area in 2011 (the Sandy Heath switchover) so
"how dare Virgin switch it off earlier than the official date"
(paraphrased).

What does the "Digital Switchover" have to do with cable TV anyway? My
understanding was that it was solely about the terrestrial broadcasts
(i.e. what people receive through an aerial).

how do you think cable services get their signals?

--
From KT24

Using a RISC OS computer running v5.11

On Tue, 29 Dec 2009 18:33:02 +0000, Duncan Corps
wrote:

On Tue, 15 Dec 2009 09:28:04 +0000, chunkyoldcortina wrote:
But residents aren't happy cos the publicity has been that Digital
Switchover happens in that area in 2011 (the Sandy Heath switchover) so
"how dare Virgin switch it off earlier than the official date"
(paraphrased).

What does the "Digital Switchover" have to do with cable TV anyway? My
understanding was that it was solely about the terrestrial broadcasts
(i.e. what people receive through an aerial).

It has nothing directly to do with cable TV. However, I can understand
people objecting to the removal of analogue TV from their cable service
before the broadcasters stop producing analogue signals in their area in
2011.

"It is still available through an aerial, why shouldn't we continue to
get it by cable?", sort of thing. There is some sort of logic to the
complaint.

--
Peter Duncanson
(in uk.tech.digital-tv)

On Tue, 29 Dec 2009 19:38:33 +0000, Peter Duncanson wrote:
On Tue, 29 Dec 2009 18:33:02 +0000, Duncan Corps
wrote:
On Tue, 15 Dec 2009 09:28:04 +0000, chunkyoldcortina wrote:
But residents aren't happy cos the publicity has been that Digital
Switchover happens in that area in 2011 (the Sandy Heath switchover)
so "how dare Virgin switch it off earlier than the official date"
(paraphrased).

What does the "Digital Switchover" have to do with cable TV anyway? My
understanding was that it was solely about the terrestrial broadcasts
(i.e. what people receive through an aerial).

It has nothing directly to do with cable TV. However, I can understand
people objecting to the removal of analogue TV from their cable service
before the broadcasters stop producing analogue signals in their area in
2011.

Since you've just confirmed my belief, if I was an affected resident and
customer then my objection would be "there's no (external) reason to
remove analogue broadcasts from cable in the first place, the Digital
Switchover certainly isn't one".

Bringing the Digital Switchover into the issue is just deliberately
creating confusion which the cable and satellite broadcasters could use
to push new products (with new prices).

I hope these people get some consumer justice :-) .

On Tue, 29 Dec 2009 19:25:24 +0000, Charles asked:

how do you think cable services get their signals?

Some cable companies get their signal for some radio and TV stations
direct from the radio or TV station rather than from an off air signal.

And the signal for some radio and TV stations is from satellite rather
than terrestrial recption.

On Tue, 29 Dec 2009 22:04:50 +0000, Duncan Corps
wrote:

On Tue, 29 Dec 2009 19:38:33 +0000, Peter Duncanson wrote:
On Tue, 29 Dec 2009 18:33:02 +0000, Duncan Corps
wrote:
On Tue, 15 Dec 2009 09:28:04 +0000, chunkyoldcortina wrote:
But residents aren't happy cos the publicity has been that Digital
Switchover happens in that area in 2011 (the Sandy Heath switchover)
so "how dare Virgin switch it off earlier than the official date"
(paraphrased).

What does the "Digital Switchover" have to do with cable TV anyway? My
understanding was that it was solely about the terrestrial broadcasts
(i.e. what people receive through an aerial).

It has nothing directly to do with cable TV. However, I can understand
people objecting to the removal of analogue TV from their cable service
before the broadcasters stop producing analogue signals in their area in
2011.

Since you've just confirmed my belief, if I was an affected resident and
customer then my objection would be "there's no (external) reason to
remove analogue broadcasts from cable in the first place, the Digital
Switchover certainly isn't one".

Bringing the Digital Switchover into the issue is just deliberately
creating confusion which the cable and satellite broadcasters could use
to push new products (with new prices).

The crucial point about the Digital Switchover is that is an Analogue
Switchoff.

I hope these people get some consumer justice :-) .

--
Peter Duncanson
(in uk.tech.digital-tv)

In article , J G Miller scribeth
thus
On Tue, 29 Dec 2009 19:25:24 +0000, Charles asked:

how do you think cable services get their signals?

Some cable companies get their signal for some radio and TV stations
direct from the radio or TV station rather than from an off air signal.


What in the UK?..

And the signal for some radio and TV stations is from satellite rather
than terrestrial recption.

Indeed they do..
--
Tony Sayer

On Wed, 30 Dec 2009 00:49:00 +0000, Peter Duncanson wrote:
On Tue, 29 Dec 2009 22:04:50 +0000, Duncan Corps
wrote:
if I was an affected resident and
customer then my objection would be "there's no (external) reason to
remove analogue broadcasts from cable in the first place, the Digital
Switchover certainly isn't one".

The crucial point about the Digital Switchover is that is an Analogue
Switchoff.

I see that.

But I thought the only thing the government/whoever was dictating was
Analogue Over Terrestrial Switchoff, and anything else (Analogue Over
Cable Switchoff, Analogue Over Satellite Switchoff) was entirely the
decision of the cable and satellite TV companies, driven by their
commercial desires.

Am I wrong?