[GreenKeys] Fwd: Re: Western Union

[Richard Knoppow]

    There is a pretty good explanation of the choice of color sub 
carrier at
https://en.wikipedia.org/wiki/Colorburst

    Keep in mind that the main purpose of broadcasting in the US 
is attracting an audience. The larger the audience the more 
remunerative the service. When color was introduced it mainly 
benefitted RCA who held most of the applicable patents. Color did 
not increase the audience, at least until long after it was 
introduced. Because color equipment and sets were expensive the 
amount of color programming and especially the number of home 
receivers grew only slowly. RCA was aware of this and its the 
principle reason they insisted in promoting "compatible" color, 
which could be received on existing B&W sets. RCA had a number of 
competitors who would have liked the FCC to adopt a 
non-compatible system. Some of them had a point some didn't CBS 
wanted color to be on UHF frequencies (which makes some sense) 
but also wanted lower resolution (I think back to 405 lines) and 
were promoting their sequential system which had very serious 
motion rendition problems. While the FCC seemed to be favoring 
the CBS system they changed their minds and adopted a combination 
of the systems proposed by RCA and others. CBS did not go to 
color for years and ABC was slow because they just didn't have 
the capital to invest in something that was not going to increase 
advertising revenue. Since the audience for color was no larger 
than for B&W no more could be charged for advertising. This 
continued for many years. Both RCA and CBS pushed for color 
because both had patents which would expire if one or the other 
system was not adopted.
     Those who are old enough to remember when B&W TV went on the 
also remember the quality was pretty awful. RCA bent over 
backward to make the initial color offerings reasonably good but 
hardly anyone saw them.
    I have no idea what this had to do with Teletype.
    As far as synchronization via power line frequency, I don't 
think early TV sets relied on it.
    A question for those who have lived in Los Angeles even 
longer than I have (there were still dinosaurs here. Up to about 
the early 1950s parts of the city had 50Hz power. DWP, operated 
by the City of LA was 60 hz but So Cal Edison and some local 
power companies were 50Hz. If you lived in the San Fernando 
Valley or Burbank you probably had 50Hz power. I rather wonder 
how well TV receivers worked on it.

On 4/25/2019 9:25 PM, David I. Emery wrote:
> On Thu, Apr 25, 2019 at 04:23:59PM -0400, Bruce Gentry via GreenKeys wrote:
>> Agreed- but TV was on the air and growing from 1946 onward. In the "good
>> old days" in small towns not on the grid, it was a problem. Many of
>> those stations still used a 60 cycle vertical and 15,750 horizontal rate
>> through the 50s if they  transmitted locally originated B&W exclusively.
>> With a 59.94 vertical rate, a set of poor design or in bad condition
>> could have a bar slowly crawling  the screen with a good steady 60 cycle
>> power source.  Many power systems in the 40s and 50s  may not have been
>> accurate enough for fax machines. The military ones I worked on used a
>> tuning fork oscillator to eliminate power frequency issues.
> 
> 	Certainly was (AND STILL IS) true that the power line frequency
> is not close enough for something like analog fax.   Today is no
> different than back then... it can be surprisingly far off over short
> periods when the grid is under heavy load - nor is it off by a fixed
> amount only slowly varying either.
> 
> 	At least until quite recently power grid controllers attempted
> to keep the number of cycles per day accurate... so electric clocks
> would on the average be right... recently in some places in the world it
> has been decided that speeding up the grid to catch up after heavy load
> has slowed it down costs too much and attempting to keep cycles per
> day/week/month right is no longer done there.   And even where it still
> is done on really hot days with huge grid wide power demand clocks can
> be slow by up to tens of seconds at certain times of day.
> 
> 	Of course a large part of this is the death of mechanical electric
> clocks based on synchronous motors and gearing...
> 
> 	HOWEVER, not an insignificant number of electronic clocks on
> line powered consumer devices don't use accurate crystal oscillators to
> keep time, but use the power line as a frequency reference to save a few
> pennies on a reasonably accurate crystal rather than a cheap ceramic
> resonator as a clock source that may be accurate only to a percent or so
> over temperature and time (plenty good enough otherwise for clocking
> logic).
> 
> 	Another curious fact here is that the 59.94/29.97 of NTSC  was a
> horrid compromise to avoid having harmonics of the horizontal scanning
> frequency interfere with the sound carrier center frequency of 4.5 MHz
> in inter-carrier sets and especially to minimize picture interference in
> color pictures from the 4.5 sound carrier in the video (sound carrier was
> 4.5 MHz away  from the video carrier and inter-carrier TVs did not have
> a separate IF for the sound and video, but simply extracted the 4.5 MHz
> beat between the two carriers out of the video detector which acted of
> course as a mixer).
> 
> 	Pretty obviously it would have trivially inconvenient to
> slightly offset the sound carrier frequency of TV stations from the
> original 4.5 MHz from the video carrier to avoid this... but some
> complete DOFUS decided instead that nothing much would be bothered by
> adjusting the basic timing of the whole video clock by 1000/1001 - so
> this didn't happen and a permanent headache for video engineers and
> equipment and protocol designers and architects was created that
> persists to this day.   HD video is still  29.97/59.94 fps in the USA.
> 
> 	The number of hours, months, years, decades, centuries,
> millenia, even eons of expensive engineering (and these days software
> engineering) time that has gone ever since into working out ways of
> dealing with 29.97 instead of 30 and 59.94 instead of 60 is
> incalculable.. particularly when this didn't happen in Europe and much
> of the rest of the world which uses 25.0 and 50.0 frames per second
> timing nor (for the most part) in Hollywood which used 24 frames per
> second displayed 48 or 96 times a second.
> 
> 	It is essentially impossible to think of any consequences of
> moving the offset between the two TV carriers of that era (of VSB analog
> TV) that would even have chewed up more than a few months here and there
> of engineering time (or service or maintenance or any other time).   At
> most before frequency counters were common it might have been a bit more
> difficult to adjust this accurately in the field.
> 
> 	And while existing sets back in 1953 would have had to be very
> slightly realigned  for optimum operation very few had filters at 4.5
> MHz tight enough to notice...
> 
> 

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL