Re: OPT equalising circuit

On May 6, 7:17=A0am, John Byrns <byr...@[EMAIL PROTECTED]
> wrote:
> In article <0BATj.7774$ko5.7...@[EMAIL PROTECTED]
>,
>
> =A0"Alex" <apogo...@[EMAIL PROTECTED]
> wrote:
> > On the stereo-decoder note, what is the phasing of 19KHz pilot with
resp=
ect
> > to the 38KHz (suppressed) carrier: do the zero-crossings coinside
(every=

> > second one) or peaks coinside (every secon ones)?
>
> > I would guess, the peaks. That way it would have been easier to derive
3=
8KHz
> > simply by a class C frequency multiplier.
>
> Your guess is incorrect, the 19 kHz pilot tone and the regenerated 38
> kHz carrier must be phased so that the zero-crossings coincide, that is
> the way the original system specification was written. =A0If the decoder
> is adjusted so that the peaks coincide it will be impossible to achieve
> any stereo separation at all. =A0If the phasing is such that the
> zero-crossings do not coincide, but are close, it is possible to achieve
> full separation by adjustment of the matrix separation control, but the
> signal to noise ratio will be degraded.
>
> Regards,
>
> John Byrns
>
> --
> Surf my web pages at, =A0http://fmamradios.com/

I see, John.
Thanks for the info.

If it is so that the sero-crossings coincide then it better suits a
PLL-based multiplier. Probably the early designers had that method in
mind, not the harmonic frequency multiplier... In case of Patrick
Turner it indeed makes no difference, because he fiddles with at least
two LC tanks to get the phase right. In his circuit the phase
adjustment is so broad, that he can possibly swap left and right
channels if he wanted to.

Regards,
Alex