But the saving of 704 rather than 720 is minuscule.I think the BBC changed their DTT channels from 720 to 704, as although
On 24/02/2022 21:15, NY wrote:
But the saving of 704 rather than 720 is minuscule.I think the BBC changed their DTT channels from 720 to 704, as although
tiny, it liberated enough bandwidth to squeeze local radio into PSB1
On 24/02/2022 21:15, NY wrote:
But the saving of 704 rather than 720 is minuscule.I think the BBC changed their DTT channels from 720 to 704, as although
tiny, it liberated enough bandwidth to squeeze local radio into PSB1
On 25/02/2022 08:12, Mark Carver wrote:
On 24/02/2022 21:15, NY wrote:
But the saving of 704 rather than 720 is minuscule.I think the BBC changed their DTT channels from 720 to 704, as although
tiny, it liberated enough bandwidth to squeeze local radio into PSB1
Fair enough, although since then they've had to make much bigger economies
to fit in BBC Three. I suppose they designed the resolution and bit rates when BBC Three was present, then benefited from a time when BBC Three was internet-only and the remaining channels could have higher bit rates, and have now reverted to the original state.
Reducing 720 to 704 is a saving of 16/720 = 2% - but for several channels
I can see that it would be enough to fit in several radio channels.
I assume that is why its in mono then. Very few of the stations on radio on Freeview are stereo. The main bbc ones, Asian network, Classic FM and not much else it seems.It's not worth having the radio stations in stereo on DTT. I suspect
When you say active lines on 625, I'm assuming you mean that sync pulses and other data like teletext were in the ones not officially seen.Blanking consumes about 25+25 lines on analogue.
Why did the 405 line use positive video, as this put the sync pulses at the lowest signal level and hence more prone to am interference like cars and vacuum cleaner interference.
On 25/02/2022 10:30, Brian Gaff (Sofa) wrote:
I assume that is why its in mono then. Very few of the stations on radioIt's not worth having the radio stations in stereo on DTT. I suspect they
on
Freeview are stereo. The main bbc ones, Asian network, Classic FM and not
much else it seems.
are aimed at consumption based on kitchen, bedroom, and hotel tellies,
where listening is a secondary activity.
When you say active lines on 625, I'm assuming you mean that syncBlanking consumes about 25+25 lines on analogue.
pulses
and other data like teletext were in the ones not officially seen.
Digital platforms do not transmit the blanking period, it would be a pointless waste of bandwidth
Why did the 405 line use positive video, as this put the sync pulses
at
the lowest signal level and hence more prone to am interference like
cars
and vacuum cleaner interference.
Wasn't the reason negative mod was adopted for 625/UHF because it pushed
the sync pulses (rather than high luminance picture content) into the non linearity 'zone' of klystrons ?
Anyway negative mod any better though for reception and impulse rejection; overshoot and all that ?
Why did the 405 line use positive video, as this put the sync pulses at
the lowest signal level and hence more prone to am interference like cars >and vacuum cleaner interference.
On 25/02/2022 10:30, Brian Gaff (Sofa) wrote:
I assume that is why its in mono then. Very few of the stations on radioIt's not worth having the radio stations in stereo on DTT. I suspect they
on
Freeview are stereo. The main bbc ones, Asian network, Classic FM and not
much else it seems.
are aimed at consumption based on kitchen, bedroom, and hotel tellies,
where listening is a secondary activity.
Wasn't the reason negative mod was adopted for 625/UHF because it pushed
the sync pulses (rather than high luminance picture content) into the non linearity 'zone' of klystrons ?
Anyway negative mod any better though for reception and impulse rejection; overshoot and all that ?
On Fri, 25 Feb 2022 10:30:53 -0000, "Brian Gaff \(Sofa\)" <briang1@blueyonder.co.uk> wrote:
Why did the 405 line use positive video, as this put the sync pulses at >>the lowest signal level and hence more prone to am interference like cars >>and vacuum cleaner interference.
And why didn't 405 line use equalising pulses?
Interesting assumption. I don't have any FM radio, apart from a) an all-in-one hifi system and b) a separate tuner, neither of which I CBA to
set up, especially since the tuner requires a 300 ohm aerial and doesn't
have a telescopic one.
"Mark Carver" <mark.carver@invalid.invalid> wrote in message >news:j7rqloFh7u3U1@mid.individual.net...
Wasn't the reason negative mod was adopted for 625/UHF because it
pushed the sync pulses (rather than high luminance picture content)
into the non linearity 'zone' of klystrons ?
Anyway negative mod any better though for reception and impulse
rejection; overshoot and all that ?
I'd always understood that the main reason for negative mod was better >rejection of impulse interference from poorly-regulated car and
motorbike (especially motorbike!) ignition systems - probably more of
an issue with spark-gap/coil ignition than with modern electronic
ignition.
"Mark Carver" <mark.carver@invalid.invalid> wrote in message news:j7rqloFh7u3U1@mid.individual.net...
On 25/02/2022 10:30, Brian Gaff (Sofa) wrote:
I assume that is why its in mono then. Very few of the stations onIt's not worth having the radio stations in stereo on DTT. I suspect
radio on
Freeview are stereo. The main bbc ones, Asian network, Classic FM and
not
much else it seems.
they are aimed at consumption based on kitchen, bedroom, and hotel
tellies, where listening is a secondary activity.
Interesting assumption. I don't have any FM radio, apart from a) an all-in-one hifi system and b) a separate tuner, neither of which I CBA
to set up, especially since the tuner requires a 300 ohm aerial and
doesn't have a telescopic one.
I use DTT or DSat for recording radio programmes (mostly Radio 4), in
exactly the same way as for TV programmes.
"Roderick Stewart" <rjfs@escapetime.myzen.co.uk> wrote in message >news:9e4k1h9ndt62ghledil4qq31k5ga07fo12@4ax.com...
On Fri, 25 Feb 2022 10:30:53 -0000, "Brian Gaff \(Sofa\)"
<briang1@blueyonder.co.uk> wrote:
Why did the 405 line use positive video, as this put the sync pulses at >>>the lowest signal level and hence more prone to am interference like cars >>>and vacuum cleaner interference.
And why didn't 405 line use equalising pulses?
What was the purpose of equalising pulses? I could never find a really good >explanation.
For several reasons, positive modulation is a real PITA. One of them is
that there is no easily-obtainable measurement of the RF signal level.
On Sun, 27 Feb 2022 08:52:43 +0000, Ian Jackson ><ianREMOVETHISjackson@g3ohx.co.uk> wrote:
For several reasons, positive modulation is a real PITA. One of them is >>that there is no easily-obtainable measurement of the RF signal level.
You can sample the black level on the back porch (as some of the
better homemade receivers did to obtain an AGC voltage), but you only
get a measure of 30% of peak, which is not as good as a 100% reference
that can be sampled with simpler circuitry. Designers of domestic
electronics being cheapskates is not a new thing.
On Sat, 26 Feb 2022 21:40:36 -0000, "NY" <me@privacy.invalid> wrote:
"Roderick Stewart" <rjfs@escapetime.myzen.co.uk> wrote in message >>news:9e4k1h9ndt62ghledil4qq31k5ga07fo12@4ax.com...
On Fri, 25 Feb 2022 10:30:53 -0000, "Brian Gaff \(Sofa\)"
<briang1@blueyonder.co.uk> wrote:
Why did the 405 line use positive video, as this put the sync pulses at >>>>the lowest signal level and hence more prone to am interference like >>>>cars
and vacuum cleaner interference.
And why didn't 405 line use equalising pulses?
What was the purpose of equalising pulses? I could never find a really
good
explanation.
Equalisation between fields of the residual charge on the integrating capacitor in the field sync separator. Without them, the line sync
pulse that immediately precedes a field sync pulse will precede it by
a whole line on alternate fields, and only half a line on the others.
The timing of the start of field scan depends on the voltage on the integrating capacitor, and if it's not equal between field scans, it
can trigger alternately late and early, and cause the lines displayed
on the screen to bunch in pairs. ("Early" translates to up, and "late"
to down). Using two or three lines of half width pulses twice as often doesn't alter the average signal voltage, so it won't interfere with
anything else, but it gives enough time for the capacitor to discharge
to a level that doesn't matter, so when the broad pulses begin, the integrating circuit has the same initial conditions on every field.
There are other ways of detecting field sync, but most early TVs used
fairly simple circuitry (essentially a resistor and a capacitor) that
didn't always work perfectly. The extra complication of adding
equalising pulses in the broadcasters' sync pulse generators obviates
the need for extra care or complication in millions of receivers, so
you might expect that as soon as the idea had been thought of it would
have been implemented everywhere, but our 405 line system never did.
Rod.
Why did the 405 line use positive video, as this put the sync pulses at the lowest signal level and hence more prone to am interference like cars and vacuum cleaner interference.
On 25/02/2022 10:30, Brian Gaff (Sofa) wrote:
  Why did the 405 line use positive video, as this put the sync
pulses at
the lowest signal level and hence more prone to am interference like
cars
and vacuum cleaner interference.
I assume they simply made the decision too soon, before they knew all
the full implications of it.
Daft question: why is it that some channels and/or some platforms
(satellite versus terrestrial) broadcast standard-definition as 704x576
and some as 720x576. There are even cases where the same channel is 704
on satellite and 720 on terrestrial (or vice versa). It looks as if the picture area is the same, but differently scaled, rather than the 704
version being the 720 version with 8 pixels either side being cropped off.
It's worse than that. There are three different formats.
1) 704x576, all pixels used, scales to 16:9 with correct aspect ratio.
2) 720x576, only the middle 704 pixels are needed to make 16:9 in the
exact correct aspect ratio. The extra 8 pixels each side may have
picture info in them from just outside the 16:9 shaped picture, or they
may be black.
3) 720x576, all pixels used, scales to 16:9 with correct aspect ratio.
On 01/03/2022 15:13, Brian Gregory wrote:
On 25/02/2022 10:30, Brian Gaff (Sofa) wrote:Indeed, there weren't that many vehicles around in 1936. Although those
  Why did the 405 line use positive video, as this put the sync
pulses at
the lowest signal level and hence more prone to am interference like
cars
and vacuum cleaner interference.
I assume they simply made the decision too soon, before they knew all
the full implications of it.
that were had absolutely no electrical suppression.
In fact, wasn't ignition suppression mandated in the 1950s, when both
cars and TVs increased in number and it was all becoming a nuisance ?!
On 01/03/2022 15:13, Brian Gregory wrote:
I assume they simply made the decision too soon, before they knew allIndeed, there weren't that many vehicles around in 1936. Although those
the full implications of it.
that were had absolutely no electrical suppression.
In fact, wasn't ignition suppression mandated in the 1950s, when both
cars and TVs increased in number and it was all becoming a nuisance ?!
On 01/03/2022 15:58, Brian Gregory wrote:
It's worse than that. There are three different formats.
1) 704x576, all pixels used, scales to 16:9 with correct aspect ratio.
2) 720x576, only the middle 704 pixels are needed to make 16:9 in the
exact correct aspect ratio. The extra 8 pixels each side may have picture
info in them from just outside the 16:9 shaped picture, or they may be
black.
3) 720x576, all pixels used, scales to 16:9 with correct aspect ratio.
Oh and it's worth mentioning that there is the same mess with 544x576 and 528x576.
I've never heard of 528x576. Is that used for any sub-SD channels on
DVB-T or DVB-S in the UK? Or is it more commonly found outside the UK?
Unlike 704/720 full-SD, I've only ever seen 544 sub-SD.
On 01/03/2022 20:51, NY wrote:
I've never heard of 528x576. Is that used for any sub-SD channels on
DVB-T or DVB-S in the UK? Or is it more commonly found outside the UK?
Unlike 704/720 full-SD, I've only ever seen 544 sub-SD.
"That's TV (UK)" Freeview channel 91 is 528x576.
The satellite version of it seems to be the same 528x576 padded with black out to 544x576.
--
Brian Gregory (in England).
On 01/03/2022 15:23, Mark Carver wrote:
On 01/03/2022 15:13, Brian Gregory wrote:
On 25/02/2022 10:30, Brian Gaff (Sofa) wrote:Indeed, there weren't that many vehicles around in 1936. Although
  Why did the 405 line use positive video, as this put the sync
pulses at
the lowest signal level and hence more prone to am interference
like cars
and vacuum cleaner interference.
I assume they simply made the decision too soon, before they knew
all the full implications of it.
those that were had absolutely no electrical suppression.
In fact, wasn't ignition suppression mandated in the 1950s, when
both cars and TVs increased in number and it was all becoming a
nuisance ?!
yes; well remembered :)
Who knows the logic of all this. Back in the early days of flat displays, some screens had oblong pixels which made the setting up of a picture on
them rather interesting.
On 01/03/2022 20:51, NY wrote:
I've never heard of 528x576. Is that used for any sub-SD channels on
DVB-T or DVB-S in the UK? Or is it more commonly found outside the UK?
Unlike 704/720 full-SD, I've only ever seen 544 sub-SD.
"That's TV (UK)" Freeview channel 91 is 528x576.
The satellite version of it seems to be the same 528x576 padded with black out to 544x576.
On 01/03/2022 17:12, Robin wrote:
On 01/03/2022 15:23, Mark Carver wrote:I'm struggling to remember the death of Queen Victoria however
On 01/03/2022 15:13, Brian Gregory wrote:
On 25/02/2022 10:30, Brian Gaff (Sofa) wrote:Indeed, there weren't that many vehicles around in 1936. Although those
Why did the 405 line use positive video, as this put the sync
pulses at
the lowest signal level and hence more prone to am interference like >>>>> cars
and vacuum cleaner interference.
I assume they simply made the decision too soon, before they knew all
the full implications of it.
that were had absolutely no electrical suppression.
In fact, wasn't ignition suppression mandated in the 1950s, when both
cars and TVs increased in number and it was all becoming a nuisance ?!
yes; well remembered :)
"Mark Carver" <mark.carver@invalid.invalid> wrote in message news:j88og1F1jl0U1@mid.individual.net...
On 01/03/2022 17:12, Robin wrote:
On 01/03/2022 15:23, Mark Carver wrote:I'm struggling to remember the death of Queen Victoria however
On 01/03/2022 15:13, Brian Gregory wrote:
On 25/02/2022 10:30, Brian Gaff (Sofa) wrote:Indeed, there weren't that many vehicles around in 1936. Although
  Why did the 405 line use positive video, as this put the sync >>>>>> pulses at
the lowest signal level and hence more prone to am interference
like cars
and vacuum cleaner interference.
I assume they simply made the decision too soon, before they knew
all the full implications of it.
those that were had absolutely no electrical suppression.
In fact, wasn't ignition suppression mandated in the 1950s, when
both cars and TVs increased in number and it was all becoming a
nuisance ?!
yes; well remembered :)
Was unsuppressed ignition only a problem for TV? Did it not cause
problems with radio reception, especially VHF which is more similar to 405-line TV? Or is VHF radio less susceptible because it is FM rather
than AM/VSB?
Ah, I can't get That's TV on terrestrial because the signal is too weak
where I live, due to a combination of factors: distance, a hill in the
...
In message <sve6n4$gl7$2@dont-email.me>, NY <me@privacy.invalid> writes
"Mark Carver" <mark.carver@invalid.invalid> wrote in message
news:j7rqloFh7u3U1@mid.individual.net...
Wasn't the reason negative mod was adopted for 625/UHF because it
pushed the sync pulses (rather than high luminance picture content)
into the non linearity 'zone' of klystrons ?
Anyway negative mod any better though for reception and impulse
rejection;Â overshoot and all that ?
I'd always understood that the main reason for negative mod was better
rejection of impulse interference from poorly-regulated car and
motorbike (especially motorbike!) ignition systems - probably more of
an issue with spark-gap/coil ignition than with modern electronic
ignition.
For several reasons, positive modulation is a real PITA. One of them is
that there is no easily-obtainable measurement of the RF signal level.
With negative mod, it's simply sync tip level, which is steady and
constant, and easy to measure with a peak-detecting meter, or as might
be displayed on a spectrum analyser.
With positive mod, it can vary between 30% (black level) and 100% (peak white). OK, there might be a few lines of VITs, but these are
essentially transient, and make peak level difficult to 'catch'.
Op 27-2-2022 om 9:52 schreef Ian Jackson:
In message <sve6n4$gl7$2@dont-email.me>, NY <me@privacy.invalid> writes
"Mark Carver" <mark.carver@invalid.invalid> wrote in message >>>news:j7rqloFh7u3U1@mid.individual.net...For several reasons, positive modulation is a real PITA. One of them
Wasn't the reason negative mod was adopted for 625/UHF because it >>>>pushed the sync pulses (rather than high luminance picture content) >>>>into the non linearity 'zone' of klystrons ?
Anyway negative mod any better though for reception and impulse >>>>rejection; overshoot and all that ?
I'd always understood that the main reason for negative mod was
better rejection of impulse interference from poorly-regulated car
and motorbike (especially motorbike!) ignition systems - probably
more of an issue with spark-gap/coil ignition than with modern >>>electronic ignition.
is that there is no easily-obtainable measurement of the RF signal
level.
With negative mod, it's simply sync tip level, which is steady and >>constant, and easy to measure with a peak-detecting meter, or as might
be displayed on a spectrum analyser.
With positive mod, it can vary between 30% (black level) and 100%
(peak white). OK, there might be a few lines of VITs, but these are >>essentially transient, and make peak level difficult to 'catch'.
And positive modulation needs more power, because almost the whole line
is between 30% and 100%.
While with negative modulation almost the whole line is between 0% and 70%. >Only the syncs are at 100%.
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