Re: Audio Precision System One Dual Domani Measuirement Systems

[Ian Jackson]

I don't know how well UK sets worked in the 1960's, but US TV sets were
not capable of receiving adjcent channels at one time, so they were not
used. For example, channel 2 was used in New York City, while the nearest
channel 3 station was in Philadelphia, 90 miles away and too far to be
received without a large antenna.

I think the next one up was 5 in NYC and 6 in Philly.

Generally, UK (and even European) TV sets had a hard time with adjacent
channels. Like the USA, the off-air broadcast channels were arranged so
that, within the normal service area, there would never be an adjacent
channel which was anything like as strong as the channel(s) intended for
that area.

The same was true of cable systems. As TV sets were incapable of
operating with adjacent channels, they carried only alternate channels.

However, things changed with the advent of cable set-top boxes. These
were specifically designed to be capable of receiving a level(ish)
spectrum of maybe 30+ channels. The tuned channel was converted to a
single output channel in Band 1 (selected to be a vacant off-air channel
in the area where the STB was to be used). Essentially, all the adjacent
channel filtering was done on output channel, so the TV set was
presented with only a single channel, thereby eliminating any problems
with poor adjacent channel selectivity.

Early STBs covered only non-off-air channels, eg 'midband' (between
Bands 2 and 3) and 'superband' (above Band 3 to around 300MHz). As a
result, large cable TV systems would carry alternate channels in Bands 1
and 3 (so that they could be received directly by the TV set), and
adjacent channels elsewhere (which could normally only be received via
the STB).

Later on, when multi-channel cable TV was recognised as 'the way to go'
by the TV set manufacturers, TV sets themselves started being equipped
with wideband tuners - typically providing virtually continuous coverage
from 50 to 300MHz and beyond, plus the UHF TV broadcast band. At the
same time, TV set adjacent channel selectivity was improved, as they had
to be capable of receiving the adjacent cable channels.

In the 1980s, SAW filters became widely available for use in domestic TV
sets, and these virtually eliminated the problems of interference from
adjacent channels. Of course, eventually, cable TV set-top boxes also
developed further, providing not only continuous wideband coverage of
from 50 to 870MHz, but they also became descramblers/decoders for pay-TV
services.

When the US started UHF TV in the mid 1960's (all 1965 models had to
have VHF/UHF tuners), they spaced the channels far apart, Philadelphia
for example had three, 17,29 and 48.

IIRC, at first, UHF was not very popular in the USA. Tuners were pretty
rudimentary - consisting of virtually nothing except a triode variable
frequency oscillator and a crystal diode mixer (techniques essentially
borrowed from WW2 radar technology), and this fed the input of the
existing VHF tuner. UHF transmitter powers were low, and as receiver
sensitivity was not much better than a crystal set, coverage was
minimal, so virtually no one bothered much with UHF TV. As a result, TV
sets continued to be manufactured fitted with only the traditional
12-channel lowband/highband VHF tuner.

Eventually, because of total congestion in the VHF TV bands, I believe
the FCC stepped in, and more or less forced TV manufactures to fit the
additional UHF tuner. I believe understand that they did this rather
indirectly - not by requiring TV manufacturers to fit UHF tuners per se,
but instead by making it illegal for them to ship TV sets across a state
border if they did not have a UHF tuner.

 

[Terry Casey]

Other western European countries[1] used system B in a 7MHz channel
width and system G in an 8MHz channel at UHF.

To use the same channels we would have needed to devise a system X with
a truncated vestigial side-band to fit our 6MHz sound-vision spacing
into 7MHz - in reality, I don't think it would have fitted!

Of course, both the British and the Irish could have simply adopted the
European systems B and G (5.5MHz sound-vision - plus the horrendous
group delay pre-correction curve).

As the UHF bands had been engineered by international agreement for 8MHz
channels to accommodate all European 625 line systems (with the vision
frequency being common to all of them), it made sense to make better use
of the bandwidth available - in fact, as we were starting from scratch,
I've often wondered why we didn't adopt the eastern European OIRT
standard with its 6MHz vision bandwidth.

As for group delay, I suppose it made sense to pre-correct the
transmission to suit the average receiver group delay response. Were the
system I parameters, without group delay correction, determined in the
belief that UK manufacturers were so much better at designing IF strips
than their continental counterparts? ;-)

Group delay was something I never thought about - until a rude awakening
doing early experimental work on Teletext - but the introduction of SAW
filters resolved the problem ...

If I remember correctly, the only
difference between systems B and G is the 7 vs 8 MHz channel spacing.
Even the VSBs are the same (0.75MHz).

Yes, but don't forget the Belgian system H with 1.25MHz vsb ...

Again, IIRC, the RoI VHF 625-line channels were the same frequencies as
the 'lettered' 625-line channels already used on many VHF cable TV
systems.

Chicken and egg situation? RTE was broadcasting using VHF 625-line
channels at least two years before BBC2 came along. I think you meant:
many VHF cable TV systems used the 'lettered' 625-line channels already
used by RTE ...

Continental systems, of course, used the CCIR broadcast channels, as
well as filling up the gaps in between ...

 

[Terry Casey]

It's just belt and braces - slightly less chance of a short if wires get
trapped by careless assembly.

It's also been changed twice!

Originally, earth wires were bare, then the requirement to cover them
with green sleeving was brought in.

Finally, the sleeving was changed from green to green/yellow ..

 

[Terry Casey]

In message <[email protected]>, David Looser

Well it might, but in practice there don't seem to have been many problems
caused by not harmonising spectrum use with the the continent. To be honest
I think the government made the right decision, the limited VHF spectrum
available in Bands 1 & 3 would only just have been enough for one extra
625-line TV channel.

[]
? - one on band I and at least one on band III, surely? I lived in
(West) Germany in the 1960s and '70s, and I'm sure we could get at least
two channels on band III (yes, I know B and G channels are narrower, but
not that much).

Were both channels available nationwide or just in densely populated
areas?

Or is German topography more amenable to providing large area coverage
with fewer transmitters?

(I'm thinking here of the German plains that we were told for many years
provided ease of access for Soviet tanks ...)

 

[Clive]

IIRC, at first, UHF was not very popular in the USA. Tuners were pretty
rudimentary - consisting of virtually nothing except a triode variable
frequency oscillator and a crystal diode mixer (techniques essentially
borrowed from WW2 radar technology),

When I have a book about faults in American NTSC sets and was surprised
to see just how cut down they were. Instead of "I" subcarrier being
1.5MHz it was reduced in the sets to 1.0 MHz because that was the same
as the "Q" subcarrier and it made the sets cheaper to produce, with of
course the lower colour accuracy, but that came second to price.

 

[Terry Casey]

Generally, UK (and even European) TV sets had a hard time with adjacent
channels. Like the USA, the off-air broadcast channels were arranged so
that, within the normal service area, there would never be an adjacent
channel which was anything like as strong as the channel(s) intended for
that area.

The same was true of cable systems. As TV sets were incapable of
operating with adjacent channels, they carried only alternate channels.

<SNIP>

The UK UHF band plan specifically avoided the use of channels n, n + 5
and n + 9 in any transmitter group (n + 5 = n + IF; n + 9 = n + 2*IF) to
prevent interference.

I was quite surprised not to find any problems with a cable system I
started work on in 1969 which used 22 adjacent VHF channels (45 -
228MHz). As the system provided financial information only, there were
no sound carriers.

All the receivers used were modified domestic receivers using the ITT/KB
VC100 chassis. This chassis was effectively the old dual standard
chassis that had gone through at least five iterations that I can
remember - VC1, VC2, VC3, VC51, VC52 - in the previous four or five
years, with all the 405-line bits left out. Consequently it was really
quite an old design.

The GPO (which was just starting to transform itself into BT) were
responsible for the RF generation and trunk distribution and had chosen
a non-standard 8.3MHz channel spacing to ensure that the local
oscillator never clashed with a vision channel. This was possibly
inherited from the ILEA schools CCTV system they'd run because the
tuning errors they'd allowed for were a joke as our receiver tuning
always had to be spot-on because of the high frequency component of the
video - think CEEFAX in vision but with 48 character[1] lines.

Despite the adjacent channel traps in the receivers still being aligned
for 8MHz spacing(!) we never encountered any problems.

All later (broadcast) CATV and SMATV systems I've encountered, though,
have always used alternate channels, as described by Ian, for channels
intended for direct reception by a domestic receiver (i.e.: without
first being received by an STB).

[1] The worst characters in the special set used in these pre-decimal
days were 10 and 11 (for tenpence and elevenpence). Of these, ten was
the worst, producing a 10101 pixel sequence for most of its height -
tuning really had to be spot on for this!

 

[J G Miller]

Were both channels available nationwide or just in densely
populated areas?

Are you talking about channels or stations?

In the analog days of television in Bundesrepblik Germany, the three public networks
ARD Das Erste, ZDF, and die Dritten Fernsehprogramme (regional TV stations)
were available nationwide but as is the case in all countries (except Netherlands
and Vlaanderen), transmitter coverage was not 100%.

In the late 1980s, two commercial networks were allowed to start terrestrial
broadcasts -- RTL and Sat Eins, but these were low power and only available
in major urban markets.

With the switch off of analog TV, all TV transmissions in Germany are now
on UHF channels. In Western Europe, only Danmark and Letzebuerg have
transmitters with DVB-t on VHF Band III.

<http://www.ukwtv.DE/sender-tabelle/>

If you want to see which stations are available in the nation's capital
and surrounding region (Berlin-Brandenburg) then take a look at
the tables at

<http://www.mabb.de/digitale-welt/dvb-t/programme.html>

Note that in order to provide a good quality SD picture with rock solid
reception, the modulation is 16-QAM 8k FFT, and only four TV stations
per multiplex. Meanwhile SDN crams 12 video streams into 64-QAM 8k FFT
with reduced FEC because commercial dross trash and profits are more important
than picture quality and reception stability in a free-market light
touch regulatory broadcast framework.

 

[Mike Tomlinson]

Finally, the sleeving was changed from green to green/yellow ..

IIRC, it was to make it easier for colour-blind people to identify.

There's also been another change: the cores in T&E (=romex) used to be
red and black for phase and neutral, now it's been harmonised with
Europe to brown and blue.

Three-phase wiring has been harmonised from red, blue and yellow for the
phases and black neutral to brown, black, black and blue neutral. Yeah,
I know...

 

[Ian Jackson]

Other western European countries[1] used system B in a 7MHz channel
width and system G in an 8MHz channel at UHF.

To use the same channels we would have needed to devise a system X with
a truncated vestigial side-band to fit our 6MHz sound-vision spacing
into 7MHz - in reality, I don't think it would have fitted!

Of course, both the British and the Irish could have simply adopted the
European systems B and G (5.5MHz sound-vision - plus the horrendous
group delay pre-correction curve).

As the UHF bands had been engineered by international agreement for 8MHz
channels to accommodate all European 625 line systems (with the vision
frequency being common to all of them), it made sense to make better use
of the bandwidth available - in fact, as we were starting from scratch,
I've often wondered why we didn't adopt the eastern European OIRT
standard with its 6MHz vision bandwidth.

As for group delay, I suppose it made sense to pre-correct the
transmission to suit the average receiver group delay response. Were the
system I parameters, without group delay correction, determined in the
belief that UK manufacturers were so much better at designing IF strips
than their continental counterparts? ;-)

With System B , I think it's the closer proximity of the TV adjacent
sound traps that create the horrendous group delay curve. In System I,
they are 0.5MHz further away, and that seems to make all the difference.

Group delay was something I never thought about - until a rude awakening
doing early experimental work on Teletext - but the introduction of SAW
filters resolved the problem ...

So you've never had the ecstatic pleasure of tuning up the group delay
pre-distortion circuit in a System B/G modulator? ;o)))))

Of course, Norway realised the SAW filters for TV set IFs could be made
with a flat group delay response (rather than slavishly mimicking the
traditional L/C horrendous "-90, +140 microsecond" curve). For reasons
unknown to me, they decided to change the pre-distortion curve of their
transmitters to something like "flat to 4MHz, and -100us at 5MHz".
Heaven knows what your average Norwegian TV set made of this!

Yes, but don't forget the Belgian system H with 1.25MHz vsb ...

I've never actually come across it. Is it actually used? I guess it's
simply a relaxation of the unnecessarily-tight VSB roll-off of System G.
However, as the TV set IFs will all be B/G, they will hardly know the
difference.

Chicken and egg situation? RTE was broadcasting using VHF 625-line
channels at least two years before BBC2 came along. I think you meant:
many VHF cable TV systems used the 'lettered' 625-line channels already
used by RTE ...

Ah! You could well be right. I only recently became aware that the Irish
launched their 625-line broadcasts in 1962, and of course, at the time,
the BBC were still only making experimental transmissions (albeit at
UHF). It's therefore unlikely that UK cable systems had any 625-line
programmes to put out until 1964 - and that would only have been BBC2.
It therefore makes sense that they adopted the Irish VHF TV frequency
plan, instead of vice versa!

 

[Terry Casey]

Are you talking about channels or stations?

Stations (sorry - copied what the OP wrote ...)

In the analog days of television in Bundesrepblik Germany, the three public networks
ARD Das Erste, ZDF, and die Dritten Fernsehprogramme (regional TV stations)
were available nationwide but as is the case in all countries (except Netherlands
and Vlaanderen), transmitter coverage was not 100%.

The OP was referring to VHF transmissions in the 60s and 70s - are you
sure you are not wandering of into UHF territory here? That would make a
considerable difference to coverage ...

 

[David Looser]

IIRC, it was to make it easier for colour-blind people to identify.

There's also been another change: the cores in T&E (=romex) used to be
red and black for phase and neutral, now it's been harmonised with
Europe to brown and blue.

Three-phase wiring has been harmonised from red, blue and yellow for the
phases and black neutral to brown, black, black and blue neutral. Yeah,
I know...

BS7671 says that the colours are brown, black and grey, with blue for
neutral.

David.

 

[Mike Tomlinson]

You mean that two of the phases are the *same* colour?
Yes.

Surely not

Unbelievable but true. Foisted on us by the Eurocrats in Brussels.

: how do
you know whether it's safe to connect two wires if they could be on
different phases?

you don't

And if you connect brown, black and black to a three phase
motor and get the two blacks the wrong way round it will run backwards.

precisely.

I can see the benefit in changing from red+black to brown+blue in T&E as
those are the same colours used in flex, but to go from our previous
widely understood red/yellow/blue + black to the new scheme is less
convincing.

The idea, I think, was to continue the concept that the brown wire is
phase and blue neutral for consistency, but to use two black wires for
the second and third phases... words fail me.

See this:

http://jasper.org.uk/ingleses.jpg

this was an installation where a distribution board built in Britain was
shipped to a remote location in Europe. The Spanish electricians needed
a crib sheet to match up the colours correctly

 

[Mike Tomlinson]

BS7671 says that the colours are brown, black and grey, with blue for
neutral.

Must have changed, then, 'cos I have seen several installations with
brown/black/black and blue. Also see the pic I posted earlier - look at
the Spanish names for the harmonised colours.

 

[David Looser]

Must have changed, then, 'cos I have seen several installations with
brown/black/black and blue.

BS7671 permits the use of other colours as long as the ends of the wires are
clearly labelled "L1", "L2" etc. I guess the installers simply didn't have
any grey cable.

Also see the pic I posted earlier - look at
the Spanish names for the harmonised colours.

L1 is brown, yet your picture has "negro" against L1, so I'm not sure that
we can place any confidence in its veracity.

David.

 

[Mike Tomlinson]

BS7671 permits the use of other colours as long as the ends of the wires are
clearly labelled "L1", "L2" etc. I guess the installers simply didn't have
any grey cable.

No, this is an armoured underground cable with cores in the colours
stated.

L1 is brown, yet your picture has "negro" against L1, so I'm not sure that
we can place any confidence in its veracity.

<shrug> I took the photo, and have seen the installation several times.
Here's another photo, since you seem to have trouble handling the truth:

http://jasper.org.uk/disboard.jpg

Let's not talk about the croc clips, shall we?

 

[J G Miller]

I've never actually come across it. Is it actually used?

Do you think there are still analog TV transmissions in Belgium, a
neighboring country whose capital is less distance (198 miles)
away from London than Edinburgh (332 miles)?

RTBF ceased the last analog TV transmissions on March 1st, 2010.

<http://www.dvb.ORG/about_dvb/dvb_worldwide/belgium/index.xml>

<

>

<

>

The VRT ceased analog TV transmissions on November 3rd, 2008.

Meanwhile analog TV transmissions continue in England and Northern Ireland ...

 

[David Looser]

No, this is an armoured underground cable with cores in the colours
stated.

Then it doesn't conform to EU harmonised colours.

<shrug> I took the photo, and have seen the installation several times.
Here's another photo, since you seem to have trouble handling the truth:

The "truth" is that the harmonised colours for three-phase are brown, black
and grey. If anyone is having problems handling the the truth then its you
I'm afraid. The photos only tell us about the one installation, who says it
conforms to the harmonised colours?

Its quite possible that the colours written-in are old pre-harmonisation
Spanish colours.

David.

 

[David Looser]

Meanwhile analog TV transmissions continue in England and Northern Ireland
...

And??

David.

 

[Dave Plowman (News)]

IIRC, it was to make it easier for colour-blind people to identify.

There's also been another change: the cores in T&E (=romex) used to be
red and black for phase and neutral, now it's been harmonised with
Europe to brown and blue.

You make it sound like 'we' were forced to adopt another country's
standard.
Flex colours were originally changed to harmonise the sales of electrical
goods across Europe - in the same way as our electricity supply became 230
volts instead of 240. Without changing a thing. ;-)
The flex colours were chosen so a colour blind person could still
differentiate between them - if, of course, he knew that the dark one was
line...

Permanent cable changed quite recently to the same colours.

Three-phase wiring has been harmonised from red, blue and yellow for the
phases and black neutral to brown, black, black and blue neutral. Yeah,
I know...

Red(L1) Yellow(L2) Blue(L3) now is Brown Black Grey

 

[hwh]

In message <[email protected]>, David Looser

Well it might, but in practice there don't seem to have been many
problems
caused by not harmonising spectrum use with the the continent. To be
honest
I think the government made the right decision, the limited VHF spectrum
available in Bands 1 & 3 would only just have been enough for one extra
625-line TV channel.

[]
? - one on band I and at least one on band III, surely? I lived in
(West) Germany in the 1960s and '70s, and I'm sure we could get at least
two channels on band III (yes, I know B and G channels are narrower, but
not that much).

There were some areas with two band III channels, Brussels for instance
on E.8 and E.10. With a bit of luck you could get a Dutch channel too or
a Frech one in the South. We got three Band III signals in Brussels
around 1966 (Belgium French and Flemish as well as France).
This of course would not have meant that full area coverage like the
whole of the UK would have been possible.

Holland had only one channel on VHF, partly because Belgium needed two
in Brussels. I think most of Germany had only one too, except if you
were close to the border between West and East (or Berlin).

For the UK two channels was possible using 405 lines because they used
narrower channels, leaving room for more channels to allocate to
transmitters. Even then, different polarization was often necessary to
separate the signals.

gr, hwh