[time-nuts] 1 pps Sync'ing

Bob kb8tq kb8tq at n1k.org
Sun Jun 24 14:27:51 EDT 2018


You can indeed do this, the question is - do you *really* want to? 

Depending a bit on your GPS module, the 1 pps output can jump around a few nanoseconds
on a second to second basis. Keeping the 100 MH edge locked implies modulating the 100 MHz
by at least a few ppb at some rate faster than 1 Hz. That will degrade the phase noise on the
outputs more than a little ….

A deeper issue is that the GPS module really isn’t reporting “GPS time” at the 1 second 
level. It’s reporting GPS Time + atmospheric noise. What you would be tracking is more the bounce
in the atmosphere than anything that GPS actually is doing. Something like an L1 / L2 receiver 
would help some with this.


> On Jun 24, 2018, at 6:37 AM, Martyn Smith <expertengineer at live.co.uk> wrote:
> Hello,
> I am a newbie question.
> I have an application where I have a 10 MHz and 100 MHz squarewave output from my GPS frequency standard.
> The frequency standard uses the PRS10 rubidium.  The 100 MHz output is just a 100 MHz VCO locked to the 10 MHz.
> These outputs are disciplined by the GPS's 1 pps (as far as frequency).  But they are not in phase with it.
> I need the rising edges of both the 10 MHz and 100 MHz squarewave outputs to be aligned with the GPS 1 pps (UTC) to within 1 ns.
> Anyone already done this?  I'm sure I've seen a distribution amplifier that does this at 10 MHz.
> But the 100 MHz is actually the more important one that I need to align.
> Regards
> Steve
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