Re: Audio Precision System One Dual Domani Measuirement Systems

[David Looser]

Of course it could, but harmonizing spectrum with the continent might
have been beneficial as well.

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.

Have these plans been published?

I read them in a copy of the Journal of the Royal Television Society
published some time around 1961. Can't be more specific than that I'm
afarid.

David.

 

[Geoffrey S. Mendelson]

Carrying a PRI relay of BBC World Service is far cheaper than
paying for NPR programming, so many smaller public radio
stations prefer this option for obvious reasons.

Didn't the Bill and Melinda Gates Foundation help pay for it?

Geoff.

 

[David Looser]

Of course it would have been better for the public, but it was better
for the Thatcher administration and business friends and supporters
to sell off the spectrum for commercial use since higher profits
could be made that way instead of tv broadcasts.

I disagree. Many of the new uses weren't about high profits but were
low-power devices used by the public such as wireless baby alarms, wireless
microphones, wireless doorbells etc. All of far more use to the public than
one more TV network IMO.

David.

 

[J G Miller]

Didn't the Bill and Melinda Gates Foundation help pay for it?

I could be wrong but I do not think that they specifically put any
money into BBC World Service on PRI affiliates. The partnership
between BBC World Service and PRI arose partly out of a joint news
program from Boston and WGBH "The World", and in response to
the BBC stopping their HF service to North America.

The Bill and Melinda Gates Foundation is active in funding a lot
of public radio and TV programming via the CPB for PBS programs
and directly with NPR, and with American Public Media (whose programs
are heard on both NPR affliates and PRI affliates).

 

[J G Miller]

Maybe you might want check out the meaning of the word consortium.

Yeah I was just plain wrong to say it was not a consortium --
I should have checked the "finer" details first.

In the case of PBS (television):

1) it is collectively owned by the affiliate stations

2) it produces no programs of its own, but these are supplied by
major stations (eg WETA, WGBH, WNET, KQED) for network viewing by
affliates who have paid the appropriate fee for the program

In the case of NPR (radio):

1) it is a corporation in its own right but stations pay to join as affiliates,
and each member station receives one vote at the annual NPR board meetings

2) NPR produces network programming to which individual stations
can subscribe

 

[Clive]

Just on the offchance that you meant this seriously I'd ask just how many
people in the UK would actually want to watch French TV?
Many TVs sold in the UK had multiband tuners, and frequency converters were
easily obtainable. So of all the many factors that stopped the British
watching French TV that one was by far and away the easiest and cheapest to
solve.

Don't forget that French SECAM had positive going Video and (I think) AM
sound.

 

[David Looser]

Don't forget that French SECAM had positive going Video and (I think) AM
sound.

True enough. But the original claim was that Britain failed re-use Bands 1 &
3 for TV as UHF only TVs couldn't receive French broadcasts. I was just
pointing that many UK TVs *could * receive VHF. You are quite correct that
French 625-line TV used +ve vision modulation and AM sound which would have
made receiving French TV on UK sets impossible even if we *had* used VHF for
625-line TV.

BTW AM sound was always used with +ve vision modulation. I'm not sure that
there was a killer reason why FM could not have been used with +ve vision
modulation, but intercarrier reception (the cheap'n'easy way to receive FM
sound with TV) wouldn't work with +ve vision modulation unless there was
significant carrier amplitude remaining at the sync tips. Normally with +ve
vision modulation the carrier amplitude at sync tips was nominally zero.

David.

 

[William Sommerwerck]

BTW AM sound was always used with +ve vision modulation. I'm not sure
that
Early US TV sets used separate video and audio IFs -- intercarrier had not
been thought of at that point.

My understanding is that "inverted" polarity was used to minimize the
effects of noise bursts on the sync pulses.

 

[Clive]

BTW AM sound was always used with +ve vision modulation. I'm not sure that
there was a killer reason why FM could not have been used with +ve vision
modulation, but intercarrier reception (the cheap'n'easy way to receive FM
sound with TV) wouldn't work with +ve vision modulation unless there was
significant carrier amplitude remaining at the sync tips. Normally with +ve
vision modulation the carrier amplitude at sync tips was nominally zero.

Many years ago I used to be in to TV and the thought at the time(often
expressed in "Television" magazine) was that the French were
deliberately different to keep manufacturing in France, hence the
positive luminance signal and AM sound. Another example of this was
what used to be called "Peritel" which was mandated for any TV sold in
France to keep out foreigners out. Who would have known at the time
that it would spread and be adopted as the now SCART socket

 

[Terry Casey]

Of course it could, but harmonizing spectrum with the continent might
have been beneficial as well. Have these plans been published?

I don't see how we could harmonize system I channels with the French 919
line channels!

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!

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.

[1] Belgium also had its own variant of the French 819 line system
crammed into a standard 7MHz channel - it must have looked truly
appalling in comparison to 625!

 

[David Looser]

That's a good part of it. The net purpose of inverted polarity was to
improve subjective dynamic range. White flecks on a grey background are
far less obvious than black ones.

Umm..No. You've both got it the wrong way round. With -ve polarity sync
pulses are more affected by noise bursts than with +ve polarity. And white
flecks are far more obvious than black. Part of the reason is that impulse
interference could greatly exceed the 100% vision carrier level, saturating
the video amplifier and, with +ve modulation, the CRT.

This was why US TVs, where -ve modulation was used from the beginning,
employed flywheel sync very early on, whilst UK TVs didn't. On the other
hand UK TVs needed peak-white limiters to prevent the CRT defocusing on to
the "whiter-than-white" interference specs.

The real benefit of -ve modulation was AGC. With -ve modulation sync tips
correspond to 100% modulation and make an easy source for the AGC bias. With
+ve modulation sync tips are at zero carrier which obviously is useless for
AGC. Instead the back-porch has to be used and many different weird and
wonderful circuits were devised to "gate out" the signal voltage during the
back porch. Due to the need to keep costs down manufacturers increasingly
turned to "mean-level AGC" in which the video signal itself was simply
low-pass filtered to form the AGC bias. This lead to receiver gain being
varied by the video content, so the black on low-key scenes was boosted
whilst the whites in high-key scenes were reduced leading to a general
greyness to everything. To me it looked awful but as the Great British
Public kept buying these sets (and they were cheaper to build) mean-level
AGC became the norm for B&W UK domestic TV receivers. One great advantage of
colour was that mean-level AGC could not be used, to give correct colour
values colour sets *had* to display a picture with a stable black-level.

David.

 

[Geoffrey S. Mendelson]

The real benefit of -ve modulation was AGC. With -ve modulation sync tips
correspond to 100% modulation and make an easy source for the AGC bias. With
+ve modulation sync tips are at zero carrier which obviously is useless for
AGC. Instead the back-porch has to be used and many different weird and
wonderful circuits were devised to "gate out" the signal voltage during the
back porch. Due to the need to keep costs down manufacturers increasingly
turned to "mean-level AGC" in which the video signal itself was simply
low-pass filtered to form the AGC bias. This lead to receiver gain being
varied by the video content, so the black on low-key scenes was boosted
whilst the whites in high-key scenes were reduced leading to a general
greyness to everything. To me it looked awful but as the Great British
Public kept buying these sets (and they were cheaper to build) mean-level
AGC became the norm for B&W UK domestic TV receivers. One great advantage of
colour was that mean-level AGC could not be used, to give correct colour
values colour sets *had* to display a picture with a stable black-level.

We have a PAL TV set that displays bright white as black.

Geoff.

 

[Ian Jackson]

Umm..No. You've both got it the wrong way round. With -ve polarity sync
pulses are more affected by noise bursts than with +ve polarity. And white
flecks are far more obvious than black. Part of the reason is that impulse
interference could greatly exceed the 100% vision carrier level, saturating
the video amplifier and, with +ve modulation, the CRT.

This was why US TVs, where -ve modulation was used from the beginning,
employed flywheel sync very early on, whilst UK TVs didn't. On the other
hand UK TVs needed peak-white limiters to prevent the CRT defocusing on to
the "whiter-than-white" interference specs.

The real benefit of -ve modulation was AGC. With -ve modulation sync tips
correspond to 100% modulation and make an easy source for the AGC bias. With
+ve modulation sync tips are at zero carrier which obviously is useless for
AGC. Instead the back-porch has to be used and many different weird and
wonderful circuits were devised to "gate out" the signal voltage during the
back porch. Due to the need to keep costs down manufacturers increasingly
turned to "mean-level AGC" in which the video signal itself was simply
low-pass filtered to form the AGC bias. This lead to receiver gain being
varied by the video content, so the black on low-key scenes was boosted
whilst the whites in high-key scenes were reduced leading to a general
greyness to everything. To me it looked awful but as the Great British
Public kept buying these sets (and they were cheaper to build) mean-level
AGC became the norm for B&W UK domestic TV receivers. One great advantage of
colour was that mean-level AGC could not be used, to give correct colour
values colour sets *had* to display a picture with a stable black-level.

Even with negative video modulation, it didn't seem to take the
Americans long to realise that they could cut costs by using AC coupling
in the video amplifier between the video detector and the CRT. [I've got
some old US monochrome TV circuits which definitely show AC coupling.]
As a result, the benefits of having an AGC line which didn't vary (much)
with video content would be essentially lost.

Regarding using the back porch as the signal reference, and deriving the
AGC from it, I recall a Wireless World article in around 1967,
describing a simple add-on circuit (which I made) which partly did this.
It worked both on 405 and 626-line signals. It wasn't intended to
improve the horrible mean-level AGC but, at the start of each video
line, it did clamp the video drive (to the cathode of the CRT) to the
black reference of the back porch. As a result, you still got the
contrast varying with video content (maybe not so much on 625), but at
least the black stayed (more-or-less) black.

 

[Ian Jackson]

Of course it could, but harmonizing spectrum with the continent might
have been beneficial as well. Have these plans been published?

I don't see how we could harmonize system I channels with the French 919
line channels!

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). 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).

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.

[1] Belgium also had its own variant of the French 819 line system
crammed into a standard 7MHz channel - it must have looked truly
appalling in comparison to 625!

I think that these had gone well before I got involved!

 

[J. P. Gilliver (John)]

The ground wires in that picture appear to be in bare copper, borne out
by the person using a multimeter with a probe resting on the ground
wire. If so, that's pretty shoddy. What's to stop it coming into
contact with the exposed hot and neutral screws on the outlet body as
the outlet is pushed back into the box?

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?

 

[J. P. Gilliver (John)]

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).

 

[Mark Zenier]

The Hoover Dam in Nevada and the Grand Coulee dam in Washington state were
also built at about the same time. The Grand Coulee Dam provided massive
amounts of electric power to the Hanford plutonium refining facility.

Hanford consisted of running Uranium through carbon moderated water
cooled reactors, and then disolving the slugs in acid and chemically
seperating out the plutonium. (Buzzword: Purex). Not all that much
power demand, but tankloads of really radioactive crap that's still
there, 65 years later.

It was aluminum smelters. (The output of which got turned into heavy
bombers during WWII). There were, postwar, seven in Washington,
two in Oregon and one in western Montana, producing about a third of
the country's Aluminum. With the increasing population's power demand
soaking up the excess and raising power prices, and new competition
from Russia and Iceland, most, or all of them, have shut down now.

Eventually, in the last incarnation of the plutonium production facilites,
the N reactor, the cooling was used to generate electrical power.

(A new use for the power is Internet server farms. Microsoft has a big
one in Euphrata, near Grand Coulee, and Google has a one down in Oregon,
at The Dalles or Hood River).

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)

 

[Dave Plowman (News)]

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.

 

[David Looser]

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).
--

In the UK Band 1 was divided into 5 channels which, with care, could just
about support one national TV network. (a few low-power fill-in transmitters
for 405-line BBC1 had to operate in Band 3)

With 8MHz channels that would reduce to 3 which I suggest is not enough for
one national network.

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.

David.

 

[Geoffrey S. Mendelson]

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.

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.

Geoff.