Re: Luma signal delay

Hi,

" BTW, do I understand correctly that the delay is explicitly introduced
by the RF modulator, that is - there's "no delay" at the output of the
AD725, and "there is" already delay at the point the luma and chroma
signal (baseband signals just as they are), leave the RF modulator? "

The AD725 sets correctly the luma/chroma delays and their voltage levels
(they are perfectly aligned for use in analog TV sets). They can be
directly used as s-video output. The problem is that the RF modulator in
the C16 and C64 has an LC circuit on the chroma path which introduces
additional 100ns delay on the chroma signal (it is easier to delay a
sinusoidal signal). As the AD725 already applied the correct delay, it will
be too much delay at the end (not talking about voltage levels which also
suffers changes). It seems inside VIC and TED there is no delay between the
color and luma signals and they have tried to set it with the RF modulator.

Thanks
Istvan

On Tue, Jan 14, 2020 at 10:09 PM HÁRSFALVI Levente <
publicmailbox_at_harsfalvi.net> wrote:

> Hi!,
>
>
> On 2020. 01. 14. 16:48, Istvan Hegedus wrote:
> > Hi All,
> >
> > Does anyone have a good suggestion how could I delay the analog luma
> > signal with approximately 90-100ns? I am trying to connect an AD725 to
> > the RF modulator and that bloody RF modulator delays the chroma signal
> > too much. I would like to get them to sync.
>
> Such trick is at least used in analog color TV sets. With the
> introduction of a modulated composite color signal, luma and chroma
> inherently slip from each other by some-100 ns after the U/V
> demodulation step (and further group delays can be introduced by the
> different bandwidth of Y and U/V). To compensate for that, luma needs to
> be slightly delayed. In older TV sets, they usually use circuits built
> around "series L / parallel C" type luma delay lines. (One can still
> find such analog delay lines (of some-10 to some-100 ns nominal delay
> values) in component catalogs, the question would be, IMHO, the circuit
> that incorporates them). Later (but still analog) TV sets probably have
> that function integrated into some video signal processor chip.
>
> BTW, do I understand correctly that the delay is explicitly introduced
> by the RF modulator, that is - there's "no delay" at the output of the
> AD725, and "there is" already delay at the point the luma and chroma
> signal (baseband signals just as they are), leave the RF modulator?
>
>
> Best regards,
>
>
> Levente
>
>