[time-nuts] GPS Locked and Unlocked Performance Comparison

Dave Brown tractorb at ihug.co.nz
Wed Feb 13 20:27:36 UTC 2008


----- Original Message ----- 
From: "Tom Van Baak" <tvb at LeapSecond.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Thursday, February 14, 2008 8:53 AM
Subject: Re: [time-nuts] GPS Locked and Unlocked Performance 
Comparison


> Hi Said,
>
> The Miller design doesn't support holdover. You can either
> run it free (using JP1, see earlier mail) or run it GPS-locked.
> I think the PLL is all of one gate and an RC filter so there's
> nothing to "hold" the EFC. See his web site for details.
>
> Right, if you pull the GPS antenna the unit quickly goes way
> off frequency. This is a side-effect of its minimalist design.
> Remember he calls it the "10 MHz Simple GPSDO". So it's
> not a GPSDO one would sell to telecom. But it works fine for
> non-critical use.
>
> Yes, the performance is nice. I've tested two earlier simple
> GPSDO prototypes from Miller and they each get better. I'll
> have a better understanding when I make the measurements
> Bruce suggested.

There's a published design very similar to James Millers from Andy 
Talbot-

http://www.frars.org.uk/cgi-bin/render.pl?pageid=1285

I think they were both published about the same time originally.
He uses a 4046 for the phase detector and suggests a decent OCXO but 
otherwise very much the same.

DaveB, NZ 




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