[time-nuts] Measuring TV delays

[Alan Melia]

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" <bill at iaxs.net>
To: "'Discussion of precise time and frequency measurement'" 
<time-nuts at febo.com>
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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