Hi Bill both the 405 line and the 625 line PAL and SECAM systems in Europe
framed at 25 fpsec prob for the same reason .....even though by 625 line
inception the sets were transistorised often except for the line output
stage.
A chat to a BBC engineer at NPL Teddington at a Time & Freq Club meeting
even before UK switched to digital suggested that timing was uncertain as
the program distribution was being done using digital signals. I believe
this made interleaving local content easier.
Alan
G3NYK
----- Original Message -----
From: "Bill Hawkins" <[email protected]>
To: "'Discussion of precise time and frequency measurement'"
<[email protected]>
Sent: Thursday, January 02, 2014 7:33 PM
Subject: Re: [time-nuts] Measuring TV delays
IIRC, the reason why NTSC has an almost 30 fps rate is that early
vacuum tube TV sets could develop heater-cathode leakage that
would put a black "hum bar" in the picture. Almost 30 allows the
bar to move through the picture in a 60 Hz power distribution
system. Seems like Europe would have had that problem.
No need for it now, but it's like the QWERTY keyboard . . .
Bill Hawkins
-----Original Message-----
From: Magnus Danielson
Sent: Thursday, January 02, 2014 12:15 PM
So, in the US and other 30000/1001 frames per second countries (formerly
NTSC), encoded time is not going to be useful for precision work. For us
in the 25 frames per second world, we only need to jam for leap-seconds
and DST change-overs, but that is enough of an upset, but can be more
easily predicted with only a few handful of bits extra information.
I prefer using MLS measurement for audio delay measurement. If you do it
right, you get 20,833 us step resolution, as a result of the 48 kHz
sampliung clock. MLS delay measurement is trivial using the Analog
Precision test-set.
Cheers,
Magnus
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