[time-nuts] VCXO in a watch timing machine

Stanley timenuts at n4iqt.com
Mon Feb 4 19:35:34 EST 2013


Yes standard size this is a  ABRACON - AOCJY1 from Newark , don't know if 
they stock 18 Mhz but you should be able to order one. First check power 
supply voltage and pin out.


----- Original Message ----- 
From: "john" <john at ic0n.org.uk>
To: <time-nuts at febo.com>
Sent: Monday, February 04, 2013 5:10 PM
Subject: [time-nuts] VCXO in a watch timing machine


> Hi
>
> I'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
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