In article ,
says...

In article , David Looser
wrote:

[Snip]


I remember hunting at the "Radio Show" in 1964 for a dual standard set that
had a proper black level clamp. I succeeded, but with difficulty.

What was it, as a matter of curiosity? I don't remember one ...

--

Terry

In article ,
says...

In article ,
J. P. Gilliver (John) wrote:
UK wiring regulations require earth (ground) wires to be sheathed in
green and yellow sleeving where it is exposed.

I have often been puzzled by this requirement. What is the reason - just
identification of the earth wire, or something else?

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

In article ,
says...

In message , David Looser
writes:
[]
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 ...)

--

Terry

In message , Ian Jackson
writes
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.
--
Clive

In article ,
Terry Casey wrote:
In article ,
says...

In article , David Looser
wrote:

[Snip]


I remember hunting at the "Radio Show" in 1964 for a dual standard set
that had a proper black level clamp. I succeeded, but with difficulty.

What was it, as a matter of curiosity? I don't remember one ...


memory says an Ekco

--
From KT24

Using a RISC OS computer running v5.16

In article ,
says...

In message , Geoffrey S.
Mendelson writes
David Looser wrote:

Of course if you are only looking for local coverage you could run several
networks in the available spectrum. But the argument was that VHF gave
better national coverage than UHF. If that is the aim then, I suggest, you'd
need both Bands 1 and 3 to give truly national coverage of just one network.
Its probable that it would be possible to add a second network that only
covered the main population centres, as Analogue Channel 5 did on UHF.

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.


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!

--

Terry

On Wed, 08 Feb 2012 12:54:56 +0000, Terry Casey wrote:

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.

In article ,
Terry Casey writes

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...

--
(\__/)
(='.'=)
(")_(")

"Mike Tomlinson" wrote in message
...
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...

You mean that two of the phases are the *same* colour? Surely not: how do
you know whether it's safe to connect two wires if they could be on
different phases? 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.

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

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


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!


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 ...

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.

In practice, if we had decided to carry on using VHF for 625 line
broadcasting, I think we would have harmonised with the Irish 8MHz
channel plan - not least because of the proximity of NI transmitters to
those in the republic.

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 ...

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!

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


--
Ian