[time-nuts] Re: World's most accurate PC clock!
cfmd at bredband.net
Sun Jul 3 20:25:18 EDT 2005
From: Brooke Clarke <brooke at pacific.net>
Subject: Re: [time-nuts] Re: World's most accurate PC clock!
Date: Sun, 03 Jul 2005 17:08:16 -0700
Message-ID: <42C87DF0.4060503 at pacific.net>
> Hi Magnus:
> Thanks for the corrections and additions, they've been made to the web page.
Great, but you still have the PAL frequency wrong, you are missing the digit
just after the decimal point!
Oh, 16,384 MHz is sometimes used in Telecom, since it nicely divide downto
2,048 MHz. There can be some nice crystals/oscillators in those frequencies.
The 19,44 MHz is usually within +/- 4.6 ppm for their 15-20 year lifespan.
Ovenized not uncommon. Voltage Control can be expected. Could be a nice
complement to normal 5 and 10 MHz crystals.
BTW. I provided you with the NTSC color burst factors.
> Have Fun,
> Brooke Clarke, N6GCE
> w/Java http://www.PRC68.com
> w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
> Magnus Danielson wrote:
> > From: Brooke Clarke <brooke at pacific.net>
> > Subject: Re: [time-nuts] Re: World's most accurate PC clock!
> > Date: Sun, 03 Jul 2005 16:09:15 -0700
> > Message-ID: <42C8701B.3070409 at pacific.net>
> >>Hi Tom:
> > Brooke,
> >>I've factored a number of the common crystal frequencies and have added
> >>their common applications, see:
> > A few notes:
> > 27 MHz is "magic" since it is a common multiple to the NTSC and PAL line
> > systems. It is used in ITU-R BT.601 compatible video systems, the base
> > frequency for MPEG and MPEG-2 timing (that used a 90 kHz clock but went to full
> > 27 MHz when they found they needed it, a bit kludgy but it works).
> > The DCF should be 77,5 kHz sharp. I found one ETSI document listing it at
> > 77,5 MHz but that was a little to high. They got an editorial comment from me
> > on that one.
> > The 32,768 kHz is used in computers all over the place for their real-time
> > hardware clock. We had it since the IBM AT, so that was a definit fix for the
> > kludgy counter trick. Ah well.
> > As for your music references, there have existed a number of frequencies that
> > have been used, not all crystal oscillators. None of them is really correct.
> > The 4,33619 MHz "PAL" frequency is incorrect. It should be 4,43361875 MHZ
> > (+/- 5 Hz). Actually, that is for PAL B, D, G, H, I and N. Typo I'd assume.
> > 1,544 MHz, 2,048 MHz, 19,44 MHz, 51,84 MHz and 155,52 MHz is standard telecom
> > frequencies. The two first ones are the traditional PDH rates (and thus
> > synchronisation frequencies), the third is the normal SDH/SONET reference
> > oscillator frequency, but 51,84 MHz and 155,52 MHz is more commonly used for
> > bit-clock reference.
> > Cheers,
> > Magnus
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