[GreenKeys] Fwd: Re: Western Union

Fri Apr 26 10:21:10 EDT 2019

Watch it change around the world:

Powerit.utk.edu/worldmap/

Here is one for just the US:

fnetpublic.utk.edu/fregradient.html

My friends and I never had a problem as we were all on the same grid segment so were synchronous. 

Peter

> On Apr 26, 2019, at 12:25 AM, David I. Emery <die at dieconsulting.com> 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...
> 
> 
> -- 
>  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
> celebration of what could have been, but wasn't and is not to be now either."
> 
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