[time-nuts] Measuring 10 MHz

Brooke Clarke brooke at pacific.net
Thu May 8 08:54:48 EDT 2008

Hi Martyn:

An important aspect is to properly set the trigger levels for each input.
A mistake I made early on was to ass-u-me that the 1 PPS trigger level should 
be half of 5 Volts, i.e. 2.5 volts, but that's very wrong.  The best approach 
is to install a BNC-T connector at the front panel and use a scope probe to 
look at the signal.  The best place to trigger is at the steepest slope.

Have Fun,

Brooke Clarke
http://www.prc68.com/P/Prod.html  Products I make and sell
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Martyn Smith wrote:
> Hello,
> Thanks to all for your replies and suggesting especially Brooke, Bruce and 
> Pete.
> I am already using the Stanford technique with the 1 kHz output.  That's how 
> I get 2 x 10E-12/sec accuracy.
> Using this technique, the accuracy should be 7.9 uHz at 10 MHz (7.9E-13). 
> But I don't reliably  achieve this.  I reliably get 20 uHz, sometimes 10 uHz 
> and  I do have resolution to parts in 10E-13, but the last digit isn't 
> reliable.
> Brooke do you do better than me here with this technique?  I see you publish 
> results with accuracy better than I can achieve, I was wondering how you do 
> it.
> I think the answer from Bruce identifies my problem.  I need to take more 
> care with my measurement techniques
> If it was easy, people wouldn't charge $20 - 50k for a box that dies it 
> well.
> Thanks all again
> Martyn 
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