[time-nuts] Re: World's most accurate PC clock!
dforbes at dakotacom.net
Sun Jul 3 20:09:51 EDT 2005
At 4:09 PM -0700 7/3/05, Brooke Clarke wrote:
>I've factored a number of the common crystal frequencies and have
>added their common applications, see:
>Brooke Clarke, N6GCE
A few more frequencies:
2.4576 MHz and its powers are universally used in baud rate
generators. It's divided by powers of 2 to make 300, 600, 1200 etc.
Other folks as Signetics used 3.6864 MHz since it's 3 * the 300 baud
stuff, which makes it better able to make the oddball frequencies
like 7200 baud (28.8K etc.)
I use 3.932160 MHz in my oscilloscope clock to make the 60 Hz
line-synchronized tick, as it's 65536 * 60 Hz. Similarly, 4.194304
MHz is 65536 * 64 Hz for a straight binary divider to 1 Hz.
Many older narrowband FM radio synthesizers using the MC145152 PLL
chip use 10.240 MHz to give 10 KHz channel spacing with its
binary-only R divider.
The telecom frequencies are 1.544 MHz = T1 bit rate, 2.048 MHz = E1
bit rate, and they have multiples of those to make DS2, DS3 etc. DS3
is 28 x 1.544 MHz. A telephone person could elaborate on this subject
to no end.
Don't forget that 6.5536 MHz crystal was used by the phone phreaks to
convert a Radio Shack DTMF keypad that came with 6.144 MHz crystal to
blue box frequencies. It's not exact, but close.
[You might be able to tell that I spend way too much time factoring
--David Forbes, Tucson, AZ
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