----- Original Message ----- From: "john" <[email protected]>
To: <[email protected]> Sent: Monday, February 04, 2013 5:10 PM Subject: [time-nuts] VCXO in a watch timing machine
HiI'm hoping to get some information on the VCXO that sits in my watch timing machine. The timer is a Chinese clone of a Witschi timer - the heart of the thing is an 18MHz VCXO marked 'SCTF 03'. There's a BNC socket that outputs the crystal frequency and a 1k pot to adjust the frequency.The snag is that I can only adjust the frequency between 18,002,359Hz and 18.000,958Hz. I have a Hewlett Packard and a Thurlby Thandar frequency counter which give me readings that broadly agree - I'm quoting the HP because I trust it more! The hardware frequency in my scope doesn't have the resolution at 18MHz, but agrees that it's fast.These figures translate to a maximum of 11.32s/day fast and a minimum of 4.63s/day fast. This is borne out in practice by the behaviour of watches - if I adjust them to 0s/day, then they are fast, but if I aim for -5s/day then they are about dot-on.So if my workings-out are correct, I can 'pull' the VCXO by 78ppm, which seems reasonable, but offset away from the nominal 18MHz. Is this a common failure of VCXOx? Can anything be done about it? The device is about 18.35mm long by 10.8mm wide (and 7.7mm high) - is this a standard size, and if so who would sell an 18MHz VCXO (UK)?Any advice gratefully received. Regards John _______________________________________________ time-nuts mailing list -- [email protected]To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nutsand follow the instructions there.
<<attachment: ocxo.JPG>>
_______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
