Blank TV screens as cable firm ditches analogue

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 ?

--
Mark
Please replace invalid and invalid with gmx and net to reply.

www.paras.org.uk

In message , Mark Carver
writes
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 ?

Many UK cable networks have now gone all-digital, so some redundant
analogue equipment could possibly have been temporarily pressed into
service to allow caption insertion (where this was not originally
possible) - even if this meant forgetting about the NICAM). However,
realistically, it was probably a lot easier and cheaper to inform the
700 customers by post.
--
Ian

In article ,
says...

In message , Mark Carver
writes
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.

Many Telewest/NTL cable systems which 'modernised' in the 1990s did
exactly this.

Yes, I became involved in this. It wan't a result of 'modernising'
though, but an essential change.

Traditionally, broadcast channels were translated onto cable channels,
so what came in, went out, good or bad!

When DTV was rolled out onto the cable networks, channel capacity was
increased by upgrading the networks for greater bandwidth but the
existing analogue channels still occupied the majority of it. Previously
unused channels - many of them adjacent to the translated off-air's were
used for the new DTV services. No problem, at first, but the the
networks I first became involved with in the DTV roll out started to
exhibit very poor performance on some channels - mainly bad MER - for no
apparent reason.

The cause was traced to the new DTT transmissions which were being
introduced from the broadcasters, which also used previously unoccupied
channels adjacent to broadcast analogue signals.

CATV modulators and translators have very good 8MHz wide channel filters
on the output. However, despite their very rapid cut-off, either side of
the channel, it was impossible to filter every out-of-channel signal,
particularly at the upper end of the channel where the FM sound and
NICAM carriers are.

What was happening was that a very small amount of the lower end of the
upper adjacent DTT channel was getting through the channel filter and
interfering with the locally generated digital signal.

By this time, the DTV roll out was well under way and, in the absence of
any more available channels, the only option was to demod the off-air
signals to baseband, use encoders to restore the NICAM signal and
remodulate ...

--

Terry

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.

Perhaps the mistake that VM made in this case was to assume that all
their (possible) customers could read ...

--

Terry

On 16 Dec, 10:36, Terry Casey wrote:

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.

Perhaps the mistake that VM made in this case was to assume that all
their (possible) customers could read ...

....but the claim is that VM didn't write to everyone in the town (when
they really needed to - people could easily be connected that they
have no record of) and/or they typically write to people so often with
junk mail that this vital communication was also binned without
reading.

Cheers,
David.

In message , Terry
Casey writes
In article ,
says...

In message , Mark Carver
writes
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.

Many Telewest/NTL cable systems which 'modernised' in the 1990s did
exactly this.

Yes, I became involved in this. It wan't a result of 'modernising'
though, but an essential change.

Traditionally, broadcast channels were translated onto cable channels,
so what came in, went out, good or bad!

When DTV was rolled out onto the cable networks, channel capacity was
increased by upgrading the networks for greater bandwidth but the
existing analogue channels still occupied the majority of it. Previously
unused channels - many of them adjacent to the translated off-air's were
used for the new DTV services. No problem, at first, but the the
networks I first became involved with in the DTV roll out started to
exhibit very poor performance on some channels - mainly bad MER - for no
apparent reason.

The cause was traced to the new DTT transmissions which were being
introduced from the broadcasters, which also used previously unoccupied
channels adjacent to broadcast analogue signals.

CATV modulators and translators have very good 8MHz wide channel filters
on the output. However, despite their very rapid cut-off, either side of
the channel, it was impossible to filter every out-of-channel signal,
particularly at the upper end of the channel where the FM sound and
NICAM carriers are.

What was happening was that a very small amount of the lower end of the
upper adjacent DTT channel was getting through the channel filter and
interfering with the locally generated digital signal.

By this time, the DTV roll out was well under way and, in the absence of
any more available channels, the only option was to demod the off-air
signals to baseband, use encoders to restore the NICAM signal and
remodulate ...

Succinctly explained. I remember when the trouble started in 1998
(presumably when the DTT test transmissions started).

The main problem was that elderly analogue TV signal processors /
translators were designed to cope only with the possibility of the
presence of adjacent off-air analogue signals. In the IF stage, they had
very deep traps (typically 70dB) to reject the lower-adjacent sound (and
possibly the NICAM) and the upper-adjacent vision. However, slightly
further out, the rejection fell to maybe only 45 to 50 dB.

This performance was still generally good enough for even equal-strength
adjacent analogue signals, but unfortunately it let part of the adjacent
digital 'haystack' signal through, and this got put out on the cable
network (albeit at a relatively low level).

On the cable network, the analogue off-air signals were usually carried
unscrambled on alternate channels, between around 500 and 550MHz. This
allowed a TV set or VCR to receive them directly, without the aid of an
analogue STB (provide it could also withstand up to 48 equal-level
analogue signals being fed into its aerial socket).

When digital signals started to be introduced on the cable networks (at
the usual -10dB wrt analogue level), often the only 'spare' spectrum
space available was the alternate gaps between the five off-air
channels. Unfortunately, the residual 'bits' of the off-air DTT signals
(which had got through the processors/translators) were also sitting
there. Being not much above the noise floor, they had previously gone
un-noticed. The result was an 'unexpected' impairment to the network
digitals.

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.
--
Ian

On Dec 16, 5:39*pm, Ian Jackson
wrote:
In message , Terry
Casey writes



In article ,
says...

In message , Mark Carver
writes
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.

Many Telewest/NTL cable systems which 'modernised' in the 1990s did
exactly this.

Yes, I became involved in this. It wan't a result of 'modernising'
though, but an essential change.

Traditionally, broadcast channels were translated onto cable channels,
so what came in, went out, good or bad!

When DTV was rolled out onto the cable networks, channel capacity was
increased by upgrading the networks for greater bandwidth but the
existing analogue channels still occupied the majority of it. Previously
unused channels - many of them adjacent to the translated off-air's were
used for the new DTV services. No problem, at first, but the the
networks I first became involved with in the DTV roll out started to
exhibit very poor performance on some channels - mainly bad MER - for no
apparent reason.

The cause was traced to the new DTT transmissions which were being
introduced from the broadcasters, which also used previously unoccupied
channels adjacent to broadcast analogue signals.

CATV modulators and translators have very good 8MHz wide channel filters
on the output. However, despite their very rapid cut-off, either side of
the channel, it was impossible to filter every out-of-channel signal,
particularly at the upper end of the channel where the FM sound and
NICAM carriers are.

What was happening was that a very small amount of the lower end of the
upper adjacent DTT channel was getting through the channel filter and
interfering with the locally generated digital signal.

By this time, the DTV roll out was well under way and, in the absence of
any more available channels, the only option was to demod the off-air
signals to baseband, use encoders to restore the NICAM signal and
remodulate ...

Succinctly explained. I remember when the trouble started in 1998
(presumably when the DTT test transmissions started).

The main problem was that elderly analogue TV signal processors /
translators were designed to cope only with the possibility of the
presence of adjacent off-air analogue signals. In the IF stage, they had
very deep traps (typically 70dB) to reject the lower-adjacent sound (and
possibly the NICAM) and the upper-adjacent vision. However, slightly
further out, the rejection fell to maybe only 45 to 50 dB.

This performance was still generally good enough for even equal-strength
adjacent analogue signals, but unfortunately it let part of the adjacent
digital 'haystack' signal through, and this got put out on the cable
network (albeit at a relatively low level).

On the cable network, the analogue off-air signals were usually carried
unscrambled on alternate channels, between around 500 and 550MHz. This
allowed a TV set or VCR to receive them directly, without the aid of an
analogue STB (provide it could also withstand up to 48 equal-level
analogue signals being fed into its aerial socket).

When digital signals started to be introduced on the cable networks (at
the usual -10dB wrt analogue level), often the only 'spare' spectrum
space available was the alternate gaps between the five off-air
channels. Unfortunately, the residual 'bits' of the off-air DTT signals
(which had got through the processors/translators) were also sitting
there. Being not much above the noise floor, they had previously gone
un-noticed. The result was an 'unexpected' impairment to the network
digitals.

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.
--
Ian- Hide quoted text -

- Show quoted text -

I said elsewhere there wasn't much of interest in the group at the
moment. I must now take it back.

Bill

On Wed, 16 Dec 2009 10:36:17 -0000, Terry Casey
wrote:

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.

This ignores the areas where Virgin Media provides an analogue MATV
service (as a result of agreements made between local councils and the
local cable company, whatever it may have been.) Since end users of
that service connect their TV directly to the cable feed and do not
have a set top box - and indeed probably do not even feature on
Virgin's customer list at all - I suspect this is the problem.

--

In article ,
says...

snip

I remember when the trouble started in 1998
(presumably when the DTT test transmissions started).

The main problem was that elderly analogue TV signal processors /
translators were designed to cope only with the possibility of the
presence of adjacent off-air analogue signals. In the IF stage, they had
very deep traps (typically 70dB) to reject the lower-adjacent sound (and
possibly the NICAM) and the upper-adjacent vision. However, slightly
further out, the rejection fell to maybe only 45 to 50 dB.


Possibly, but not the cause of the problem. In any case, 8MHz wide SAW
channel filters were available and widely used in subscribers' STBs as
IF filters, so I'm fairly certain that they would have been used in all
but the most ancient head-end kit as well.


This performance was still generally good enough for even equal-strength
adjacent analogue signals, but unfortunately it let part of the adjacent
digital 'haystack' signal through, and this got put out on the cable
network (albeit at a relatively low level).

No filter, including a SAW with extremely channel edge roll-off, could
ever have prevented the problem - the simple answer is that the two
channels OVERLAP!

I've just been playing around with some figures, just to make sure that
my memory isn't playing tricks, so here goes!

This list shows all the relative data for two adjacent channels:

MHz
566.00 Channel boundary (limit of vestigial sideband)
E33 567.25 Vision carrier
570.00 Channel centre
573.25 FM sound carrier
573.802 NICAM carrier
574.00 Channel boundary (limit of vestigial sideband)
E34 575.25 Vision carrier
578.00 Channel centre
581.25 FM sound carrier
581.802 NICAM carrier
582.00 Channel boundary

DTT transmissions, of course, occupy the entire 8MHz channel.

Now, apart from the reality that no filter known to man can pass the
full 8MHz with such a rapid cut-off that nothing above or below it can
get through it, just look at how close the NICAM carrier is to the
adjacent channel - 198kHz!

But the NICAM signal has a 700kHz bandwidth, so the ch 33 NICAM signal
actually extends from about 573.45MHz to 574.15MHz, so approximately
150kHz of the upper sideband is actually inside the upper adjacent
channel!

If NICAM hadn't been invented, it should have been possible to improve
the filtering in the 750kHz gap between the FM sound carrier and the
upper channel boundary but, with NICAM, it was impossible!

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!

--

Terry

In article , [email protected]
0spam.want.no.spam.zzz says...

On Wed, 16 Dec 2009 10:36:17 -0000, Terry Casey
wrote:

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.

This ignores the areas where Virgin Media provides an analogue MATV
service (as a result of agreements made between local councils and the
local cable company, whatever it may have been.) Since end users of
that service connect their TV directly to the cable feed and do not
have a set top box - and indeed probably do not even feature on
Virgin's customer list at all - I suspect this is the problem.

This does NOT ignore areas where VM provides an analogue MATV service
(as a result of agreements made between local councils and the local
cable company, whatever it may have been.)

Which part of THIS IS AN EXCEPTION TO THE RULE did you not understand?

--

Terry