What Uses Color Decoders
Every TV monitor and TV receiver (or projector) that displays video from
composite video or S-video sources has a color decoder.
VCR's and laserdisk players do not have color decoders because, although they
may isolate the luminance and chrominance from composite video, they do not
decode the chrominance signal.
The NTSC color decoder takes the chrominance (color) signal modulated on a
subcarrier and demodulates it to obtain two color difference signals such as Pb
and Pr. Then it recreates red, green, and blue content signals (RGB) from the
color difference signals and the luminance signal using mixtures of the latter
three signals or by performing a matrix transformation. Although this discussion
is for NTSC, PAL uses a similar color decoder.
A comb filter or (less expensively) a bandpass filter is used to isolate the
chrominance content from the total content of composite video. For S-video, the
chrominance signal is already separate from the luminance.
To reduce artifacts in the picture, the 3.58 Mhz (actually 3,579,545.4 Hz)
subcarrier is suppressed as much as possible from the chrominance signal.
In order to decode the color signal, a pure 3.58 Mhz subcarrier signal in the
proper phase is needed. It is generated locally by the color decoder. At the end
of every scan line, in a part of the waveform called the back porch, there are
about eight cycles of the subcarrier used for synchronizing. So long as the
local oscillator does not gain or lose more than a quarter of a cycle in 63.5
microseconds (one scan line time) these "color bursts" will keep the local
oscillator in sync. and in phase
Quoting George <w2yj@highstream.net>:
> I thought there was a reply earlier today or yesterday explaining that
> this
> was probably a color burst crystal frequency? The note indicated that
> the
> power was turned off in the house and the signal disappeared???
> Can anyone verify that the signal is not internally generated by our
> modern
> electronic "things"?
> Help me understand.
> George
> ----- Original Message -----
> From: "David S.McCallum" <w7sac2@cox.net>
> To: <tentec@contesting.com>
> Sent: Wednesday, January 05, 2005 6:41 PM
> Subject: Re: [TenTec] RE 28.634
>
>
> > sent mine last night from N/W Fla
> >
> > David S. McCallum/USAF RET./CMSGT/W7sac/4
> > ----- Original Message -----
> > From: "Dave Edwards" <kd2e@comcast.net>
> > To: <tentec@contesting.com>
> > Sent: Wednesday, January 05, 2005 6:45 AM
> > Subject: Re: [TenTec] RE 28.634
> >
> >
> > So how 'bout some beam headings?
> > Let's see if it can be triangulated (sp?)
> > at all!!
> > I'll check myself when I get home.
> >
> > ...Dave
> > ----- Original Message -----
> > From: "Tommy Bennwik" <bennwiktv@hotmail.com>
> > To: <tentec@contesting.com>
> > Sent: Wednesday, January 05, 2005 4:30 AM
> > Subject: [TenTec] RE 28.634
> >
> >
> >> 28.364 & 14.317 abt S-2 in Stockholm. Hiding under my bed!
> >> SM0PCA /Tommy
> >>
> >>
> >> _______________________________________________
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> >> TenTec@contesting.com
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> > TenTec mailing list
> > TenTec@contesting.com
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> >
> >
> > --
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> > Version: 7.0.300 / Virus Database: 265.6.8 - Release Date: 1/3/05
> >
> >
> >
> >
> > --
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> >
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> >
> >
>
>
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