[time-nuts] GPS Locked and Unlocked Performance Comparison

Tom Van Baak tvb at LeapSecond.com
Wed Feb 13 19:53:13 UTC 2008


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.

/tvb

----- Original Message ----- 
From: SAIDJACK at aol.com
To: tvb at leapsecond.com ; time-nuts at febo.com
Sent: Wednesday, February 13, 2008 11:03 AM
Subject: Re: [time-nuts] GPS Locked and Unlocked Performance Comparison


Hi Tom,

I wonder how the Miller unit would perform if the GPS is kept alive during holdover.

If the Jupiter continues to generate the 10KHz and 1PPS from it's internal TCXO even without GPS reception then I would
expect the holdover performance to degrade to that of the TCXO if the unit goes into antenna-related holdover?

Unless the Miller design removes the 10KHz reference from the PLL if there are less than a certain number of sat's
received etc. Should be possible to add that feature by monitoring the RS232 output, gating the 10KHz, and clamping the
EFC control voltage -  if that feature is not already there.

That's a nice behavior trait of the Motorola receiver: it shuts off it's 1PPS when there are less than 4 Sats etc (in
TRAIM mode).

It's surprising what kind of performance can be achieved with the 10KHz locking the OCXO through an Exor gate. Then
again that design get's to compare phase 10.000 times more often per second than all of the other 1PPS based PLL's :)

bye,
Said

In a message dated 2/13/2008 10:47:44 Pacific Standard Time, tvb at LeapSecond.com writes:
The other is to remove the power/data connector to the Jupiter
board (which is what I did).






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