From: Alan Pearce <kiwiantipodean@googlemail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Thu, 26 Nov 2020 03:06:27 -0800
Subject: Re: [OT] Hyperikon Retrofit LED Tubes Without Ballast and
 fluorescent	lamps and TV!
Thread-Topic: [OT] Hyperikon Retrofit LED Tubes Without Ballast and
 fluorescent	lamps and TV!
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>  the European PAL system switched the chroma phase 180 degrees
> on adjacent lines (since the image is interlaced, perhaps this
> works out to just being a phase switch on each field).

Only the phase of the colour burst was changed on alternate lines so
that the phase lock of the colour subcarrier generator in the TV set
averaged out any phase shift in the transmission link. This gave a
more stable colour display than the NTSC system which could get
accumulated phase shift between the colour signal and the colour burst
(resulting in the moniker "Never Twice the Same Colour" for NTSC).

On Wed, 25 Nov 2020 at 23:42, Harold Hallikainen
<harold@mai.hallikainen.org> wrote:
>
> On the TV fluorescent lamps, yes the frequency was much higher than the
> frame rate (though I don't remember what it was).
>
> NTSC television is interesting! It's described at
> http://mai.hallikainen.org/org/FCC/FccRules/2021/73/682/ . Prior to color=
,
> the field rate was indeed 60 Hz, the power line frequency, to avoid
> rolling "hum bars." With color, it appears everything is based on a
> precise 5 MHz with the chroma subcarrier being 5 MHz * 68/88. The
> horizontal scan rate is 2/455 * the chroma subcarrier frequency. The fiel=
d
> rate is then 2/525 * the horizontal scan frequency. I think that the
> frequencies were chosen such that dots created by the chroma signal would
> be white on one scan and black on the next, letting the eye cancel them
> out. Similarly, the European PAL system switched the chroma phase 180
> degrees on adjacent lines (since the image is interlaced, perhaps this
> works out to just being a phase switch on each field). Chroma phase error
> resulted in a hue shift, but in opposite directions on adjacent lines. So=
,
> the eye averaged them out to avoid hue shift due to chroma phase drift.
> Clever!
>
> On light flicker, movie projectors used to use an incandescent "exciter"
> lamp to light the sound track. Light would pass through the film to a
> photocell. At first, the film density was varied to carry the audio, but
> later the black to white area (width of a white or black stripe on the
> film) was varied to carry the sound. Of course, if the lamp was powered b=
y
> 60 Hz, you'd get 120 Hz hum in the sound. So, the obvious solution would
> be to run the lamp on DC. But, many projectors instead ran the exciter
> lamp on high frequency AC. There was a power oscillator to drive the
> exciter lamp.
>
> On the NE-2, one of my earliest project was an NE-2 based relaxation
> oscillator running off a B battery. Choosing component values, I could ge=
t
> a light flasher or get audio out of it.
>
> Harold
> http://w6iwi.org
>
>
>
>
>
> --
> FCC Rules Updated Daily at http://www.hallikainen.com
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