From: "Poul-Henning Kamp" <[EMAIL PROTECTED]>
Subject: Re: [time-nuts] World's most accurate PC clock!
Date: Mon, 04 Jul 2005 09:49:14 +0200
Message-ID: <[EMAIL PROTECTED]>
> In message <[EMAIL PROTECTED]>, Magnus Danielson writ
> es:
>
> >> days and generate the 14.318MHz by PLL instead.
> >
> >Which should be an approximation to 14,31818 MHz I would assume, since that
> >is
> > 2
> >2 *5*715909 Hz, but an approximation to that would be quite acceptable
> >considering it is usually +/- 100 ppm (for real TV uses it should be
> >+/- 3 ppm). Ever measured what is actually there in PLLed cases? (curiosity)
>
> The correct frequency is 315/88 MHz, but that is not the original derivation
> of it. I found the real derivation on the web some time back, but now
> I can't seem to find it again.
The authorative reference is the ITU-R BT.470-6. In table 2, table item 2.11
you find
for NTSC: for PAL (B, D, G, H, I, K, N) for PAL (M) for PAL (M combi)
455 1135 1 909 917 1
f = --- f f = (---- + ---)f f = ---f f = (--- + ---)f
SC 2 H SC 4 625 H SC 4 H SC 4 625 H
where f is (in table 1)
H
15750000
f = -------- f = 15625 f = 15625 f = 15625
H 1001 H H H
I'm not covering SECAM here thought...
Notice that Note 1 in table 1 needs to be read in order to read the correct
value. The ratio-notation is not used in BT.470, but is used in other NTSC
related documents.
> >One should figure out which pin is the input to the CMOS inverter usually
> >used
> >in such oscillators. This is where the signal shall be fed in.
>
> Not all of them use a cmos inverter any more, so the data sheet should be
> consulted.
Note taken!
Cheers,
Magnus
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