Ian Jackson wrote:

In message , Arny Krueger
writes

"Terry Casey" wrote in message
...


A couple of questions regarding that list:

Why is the HRC channel spacing offset[1] by 300Hz - 6.0003MHz instead of
6MHz?

I don't know.

I recall once specially tweaking a UK 8MHz HRC harmonic comb generator
(to which all of the TV channels were locked). It was a little above (or
was it below?) 8MHz. There was a reason for this, but at the moment, I
can't remember what it was. However, I have a feeling the reason was a
bit of a red herring. I also remember tweaking another so that one of
UHF cable channels was carefully offset from a local off-air in order to
minimise the visibility of interference patterning (essentially the same
fix as discussed below).

Why are the IRC channels offset from broadcast channels (where they
exist) by 12.5kHz?

If memory sserves, two transmitters that are interferring just a little,
produce nasty herringbones if they are running at the same frequency, but
move them apart a tad, and the artifacts are far less objectionable.

That is almost certainly the reason. Running IRC channels exactly on
frequency can result in unacceptable beat patterns of 0.75 and 1.25MHz
(at least, it did on one European system I was involved with). Moving
all 65 channels HF by 25kHz worked wonders. [This is close to the 5/3 x
15.625kHz offset broadcasters use for off-air 625-line TV.] 12.5kHz will
probably also be a good offset.

[1] UK cable systems mostly use HRC at 8MHz spacing but this is
sometimes varied by a carefully calculated amount so that one block of
UHF channels coincides almost exactly with the broadcast frequencies.
This is done on systems with a by-pass facility to allow a few channels
- usually the local off-airs - to be fed directly to the TV giving the
subscriber direct access from the TV without needing an aerial.

Obviously this block of channels has to be chosen so as not to conflict
with local transmitters, so the offset will vary from system to system

US cable systems ran on some of the same channels as local broadcasters.

These days, UK cable TV systems don't seem to avoid clashing with (or,
at least, partially overlapping) the off-air TV channels (which are all
UHF). Obviously, to prevent interference problems caused by
ingress/egress, sufficient attention has to be paid to the RF-tightness
of the network.


HRC = Harmonically Related Channels. That means that of the carriers
are all multiples of an integer to reduce IMD. I designed and built
some headends in the early '80s.


--
You can't have a sense of humor, if you have no sense.

David Looser wrote:

"Michael A. Terrell" wrote in message
m...

"Geoffrey S. Mendelson" wrote:

hwh wrote:
On 2/5/12 7:04 PM, J. P. Gilliver (John) wrote:
But you've got to remember that this is the country that kept 405-line
going for, I think, longer after 625 started than it had been going
before that.

Erm, 405 started before the war and was alone until 1964? Then it
continued for another 20 years?

Someone said the last two years of 405 line signals were generated by an
unusal
method, I think the word they used was "endearing". What was it?

BTW, the BBC shut down TV broadcasts in for World War II, and resumed
them at the exact point in the same broadcast after the war. :-)


That's very easy to do with film. I should know. I loaded and ran
truckloads of 16 mm film on a pair of RCA TP66 projectors in the '70s.

I'm sure it is, but as we've already established that the "exact point in
the same broadcast" bit isn't true its not relevant.

The myth that the engineers simply ceased transmission half-way through a
programme and left the station like a sort of Mary Celeste has been
widespread, but it is a myth. In fact there was an orderly shut down and the
film in the machines would have been rewound and put into storage before the
staff left. It would have been 35mm film (the BBC didn't have facilities for
transmitting from 16mm film pre-war) and thus on nitrate stock. NOT putting
it into proper storage would have constituted a fire hazard and been in
contravention of fire regulations.


It still would have been no problem to load and start it at exactly
the same frame, if they had wanted to.


--
You can't have a sense of humor, if you have no sense.

Mike Tomlinson wrote:

Andy writes

No, the phases are *NOT* brown, black& black, they are brown, black and
grey - with blue as neutral.

I refer you to the photo I posted a link to elsewhere.

As others have noted, that installation might be wired in those colours,
but they are not the proper ones, and have not been forced on the UK as
you seem to insist ...

David Looser wrote:

"Michael A. Terrell" wrote

They had UK outlets, and the 'voltmeter was about 1/2" * 3/4" like the
tiny VU meters that were popular 30 years ago in battery powered tape
recorders.


Now that I *would* like to see a photo of, because I cannot imagine what
they look like from that description. Wherabouts on the socket faceplate is
the meter fitted? You say they have UK outlets, so why are they not
available here? Why would the Chinese make UK sockets and only sell them in
Florida? it makes no sense.

I'm also still puzzled by the claim that "tourists" are buying socket
outlets in flea markets in the US to bring home with them. Socket outlets
are simply far too cheap here to make it worth the bother and expense of
purchasing with foreign currency and then having to pack in one's
weight-limited luggage.


They were a dollar. This isn't the same as what I saw, but it will
give you some idea:
http://i00.i.aliimg.com/photo/v0/255041326/DZ_909A_6_way_power_outlet_with.jpg
since the meter was next to the power switch and cord.


"Look what I've brought you as a souvenir of my holiday in Florida, its a
cheaply made Chinese copy of a BS1363 outlet",

I can't see it somehow!

David.


--
You can't have a sense of humor, if you have no sense.

"Don Pearce" wrote in message
...
On Thu, 09 Feb 2012 16:30:25 -0500, "Michael A. Terrell"
wrote:


David Looser wrote:

"Michael A. Terrell" wrote in message
...

J G Miller wrote:

All because of the perceived need to produce weapons of mutual
annihilation.


We wouldn't need to do it, if you Europeans would stop starting
World
Wars.


According to the history books the US entered WW2 because it was
attacked by
the Japanese. It seems that Michael A. Terrell thinks that Japan is in
Europe.


Sigh. America was supplying AKA: LENDING planes and other war
materials to help Europe clean up their mess, long before Japan attacked
Pearl Harbor. Is the school system really that bad where you grew up?

Lend-lease was hardly decisive in the 1939-1941 period. The planes that
denied Goering air-superiority over Britain were all British designed and
built and flown overwhelmingly by British pilots (with some from
Czechoslovakia and Poland).

I hope you are not imagining that America did that from anything other
than good, solid self-interst.

And its worth pointing out that the country that did far more than any other
to defeat Nazi Germany was the Soviet Union. Once Hitler made the fatal
mistake of invading the USSR he sealed the fate of his regime. The most
probable outcome had the US not entered the European [1] war would have been
Soviet hegemony over most of Europe, rather than just the Eastern part. The
implications of that for the post-war balance of power are obvious.

[1] The US didn't have the luxury of deciding whether or not to enter the
Pacific war, unless, of course, it chose to cease to have any presence in
the Pacific region.

David.

"Dave Plowman (News)" wrote:

In article ,
Michael A. Terrell wrote:
The fact there are multiple grades says much. Better to use an entirely
different connector for arduous duty. Then there is no danger of mixing
them up.

How do you confuse the bright orange medical grade with the ivory
white or brown consumer hardware?

You expect a cleaner or whatever to know the difference? If the plug fits
someone will manage to get it wrong.


You think so? That will get them fired in a hospital. They are
strictly used for medical equipment, and there are plenty of industrial
grade outlets that are installed for other uses. Why would a lazy
janitor pull a heavy machine away from a wall to plug in something, when
there are empty outlets in plain sight, and spaced 10' or less apart?
The vacuums & floor scrubbers have 25 foot cords.

--
You can't have a sense of humor, if you have no sense.

"Michael A. Terrell" wrote in message
...


They were a dollar. This isn't the same as what I saw, but it will
give you some idea:
http://i00.i.aliimg.com/photo/v0/255041326/DZ_909A_6_way_power_outlet_with.jpg
since the meter was next to the power switch and cord.

Right. You started all this by refering to European sockets which had to be
installed in equipment racks. So I naturally assumed that you were talking
about UK specific installation sockets being sold in flea markets in the US.

But now I realise that you are talking about plug-in extention sockets, and
I notice from the photo that that one has "universal" sockets that will
accept US and a variety of European plugs as well as UK ones. Personally I
wouldn't touch one of those with a barge-pole. Those sort of "universal"
sockets rarely make good contact whilst the meter is clearly for show, it
would tell you nothing useful. I'm sure it would not be legal to sell those
here as the sockets appear not to have shutters, which probably explains why
I've not seen one.

David.

In message , Michael A.
Terrell writes




Do you know that the channel combiners in a CATV head end
were wired in odd and even banks, on separate groups to prevent IMD
caused in the passive mixing?

It might have depended on whose combiners you were using.

I hadn't heard about this so, one day (it must have been back in the
80s), I decided to do a quick test to see if it was true. To be honest,
I don't think I saw much difference whichever way I grouped the
channels. From what I remember, with the modulators putting each out
60dBmV, all the intermod products were at least 85dB down, and were
rather difficult to measure quickly. Such low levels of intermod would
have had a negligible impact on the overall system performance.



--
Ian

In article ,
says...

"Zero Tolerance" wrote in message
...
On Thu, 09 Feb 2012 18:17:34 +0000 (GMT), charles
wrote:

Since AP was the home of BBC News, why should this have happened. Much
more likely is that someone made "an Entertainment Tape" as a "spoof".

You can see it for yourself here. If it's a spoof then the BBC has
presented it in a rather misleading manner.

http://news.bbc.co.uk/1/hi/entertainment/3585041.stm

(The video - in nasty "RealVideo" format - purports to be a recording
exactly as broadcast, although I don't think they had work experience
juniors blindly cropping things to 14:9 back in 1964 so that
particular aspect of the presentation must be discounted.)

Yes, that's the recording. The DVD is in 4:3 so yes, that particular aspect
of the presentation can be discounted.


That isn't the film I saw - the film even has sound! And it wasn't a
telerecording either.

It was shot at Alexandra Palace that night and is a fairly long shot
which makes the whole thing look even more haphazard. Until now, I
didn't realise that I'd heard part of the bulletin that wasn't
broadcast!

It was part of a much longer film shown in the Alexandra Palace studio
at the exhibition to celebrate the 75th anniversary of the opening of
the Television Service last November.

Perhaps it is available on the APTS website somewhere?

http://www.apts.org.uk/

--

Terry

In article ,
says...

"Terry Casey" wrote in message
...
In article ,
lid says...

[1] UK cable systems mostly use HRC at 8MHz spacing but this is
sometimes varied by a carefully calculated amount so that one block of
UHF channels coincides almost exactly with the broadcast frequencies.
This is done on systems with a by-pass facility to allow a few channels
- usually the local off-airs - to be fed directly to the TV giving the
subscriber direct access from the TV without needing an aerial.

Obviously this block of channels has to be chosen so as not to conflict
with local transmitters, so the offset will vary from system to system
and can't be fixed as in the US table


In case it isn't clear, I should have pointed out that normal cable
reception is via a set top box and, of course, I was referring to
analogue systems ...

The advent of TV sets that could tune the cable channels all by themselves
was a game changer.

They are used on the continental cable systems but never have been in
the UK. Possibly because there is much more encrypted subscription
content?

--

Terry